Posted on Leave a comment

ASP.NET Core and Blazor updates in .NET Core 3.0

Daniel Roth


Today we are thrilled to announce the release of .NET Core 3.0! .NET Core 3.0 is ready for production use, and is loaded with lots of great new features for building amazing web apps with ASP.NET Core and Blazor.

Some of the big new features in this release of ASP.NET Core include:

  • Build rich interactive client-side web apps using C# instead of JavaScript using Blazor).
  • Create high-performance backend services with gRPC.
  • SignalR now has support for automatic reconnection and client-to-server streaming.
  • Generate strongly typed client code for Web APIs with OpenAPI documents.
  • Endpoint routing integrated through the framework.
  • HTTP/2 now enabled by default in Kestrel.
  • Authentication support for Web APIs and single-page apps integrated with IdentityServer
  • Support for certificate and Kerberos authentication.
  • Integrates with the new System.Text.Json serializer.
  • New generic host sets up common hosting services like dependency injection (DI), configuration, and logging.
  • New Worker Service template for building long-running services.
  • New EventCounters created for requests per second, total requests, current requests, and failed requests.
  • Startup errors now reported to the Windows Event Log when hosted in IIS.
  • Request pipeline integrated with with System.IO.Pipelines.
  • Performance improvements across the entire stack.

You can find all the details about what’s new in ASP.NET Core in .NET Core 3.0 in the What’s new in ASP.NET Core 3.0 topic.

See the .NET Core 3.0 release notes for additional details and known issues.

Get started

To get started with ASP.NET Core in .NET Core 3.0 install the .NET Core 3.0 SDK.

If you’re on Windows using Visual Studio, install Visual Studio 2019 16.3, which includes .NET Core 3.0.

Note: .NET Core 3.0 requires Visual Studio 2019 16.3 or later.

There is also a Blazor WebAssembly preview update available with this release. This update to Blazor WebAssembly still has a Preview 9 version, but carries an updated build number. Blazor WebAssembly is still in preview and is not part of the .NET Core 3.0 release.

To install the latest Blazor WebAssembly template run the following command:

dotnet new -i Microsoft.AspNetCore.Blazor.Templates::3.0.0-preview9.19465.2

Upgrade an existing project

To upgrade an existing ASP.NET Core app to .NET Core 3.0, follow the migrations steps in the ASP.NET Core docs.

See the full list of breaking changes in ASP.NET Core 3.0.

To upgrade an existing ASP.NET Core 3.0 RC1 project to 3.0:

  • Update all Microsoft.AspNetCore.* and Microsoft.Extensions.* package references to 3.0.0
  • Update all Microsoft.AspNetCore.Blazor.* package references to 3.0.0-preview9.19465.2

That’s it! You should now be all set to use .NET Core 3.0!

Join us at .NET Conf!

Please join us at .NET Conf to learn all about the new features in .NET Core 3.0 and to celebrate the release with us! .NET Conf is a live streaming event open to everyone, and features talks from many talented speakers from the .NET team and the .NET community. Check out the schedule and attend a local event near you. Or join the Virtual Attendee Party for the chance to win prizes!

Give feedback

We hope you enjoy the new features in this release of ASP.NET Core and Blazor in .NET Core 3.0! We are eager to hear about your experiences with this latest .NET Core release. Let us know what you think by filing issues on GitHub.

Thanks for using ASP.NET Core and Blazor!

Daniel Roth
Daniel Roth

Principal Program Manager, ASP.NET

Follow Daniel   

Posted on Leave a comment

Azure SignalR Service now supports Event Grid!



Since we GA’ed Azure SignalR Service in last September, serverless has become a very popular use case in Azure SignalR Service and is used by many customers. Unlike the traditional SignalR application which requires a server to host the hub, in serverless scenario no server is needed, instead you can directly send messages to clients through REST APIs or our management SDK which can easily be used in serverless code like Azure Functions.

Though there is a huge benefit which saves you the cost of maintaining the app server, the feature set in serverless scenario is limited. Since there is no real hub, it’s not possible to respond to client activities like client invocations or connection events. Without client events serverless use cases will be limited and we hear a lot of customers asking about this support. Today we’re excited to announce a new feature that enables Azure SignalR Service to publish client events to Azure Event Grid so that you can subscribe and respond to them.

How does it work?

Let’s first revisit how serverless scenario in Azure SignalR Service works.

  1. In serverless scenario, even you don’t have an app server, you still need to have a negotiate API so SignalR client can do the negotiation to get the url to SignalR service and a corresponding access token. Usually this can be done using an Azure Function.

  2. Client will then use the url and access token to connect to SignalR service.

  3. After clients are connected, you can send message to clients using REST APIs or service management SDK. If you are using Azure Functions, our SignalR Service binding does the work for you so you only need to return the messages as an output binding.

This flow is illustrated as step 1-3 in the diagram below:

Serverless workflow

What’s missing here is that there is no equivalent of OnConnected() and OnDisconnected() in serverless APIs so there is no way for the Azure function to know whether a client is connected or disconnected.

Now with Event Grid you’ll be able to get such events through an Event Grid subscription (as step 4 and 5 in the above diagram):

  1. When a client is connected/disconnected to SignalR service, service will publish this event to Event Grid.

  2. In Azure function you can have an Event Grid trigger and subscribe to such events, then Event Grid will send those events to the function (through a webhook).

How to use it?

It’s very simple to make your serverless application subscribe to SignalR connection events. Let’s use Azure function as an example.

  1. First you need to make sure your SignalR Service instance is in serverless mode. (Create a SignalR Service instance if you haven’t done so.)

    Enable serverless mode

  2. Create an Event Grid trigger in your function app.

    Create Event Grid trigger

  3. In the Event Grid trigger, add an Event Grid subscription.

    Add Event Grid Subscription

    Then select your SignalR Service instance.

    Select SignalR Service instance

Now you’re all set! Your function app is now able to get connection events from SignalR Service.

To test it, you just need to open a SignalR connection to the service. You can use the SignalR client in our sample repo, which contains a simple negotiate API implementation.

  1. Clone AzureSignalR-samples repo.

  2. Start the sample negotiation server.

    cd samples\Management\NegotiationServer
    set Azure__SignalR__ConnectionString=<connection_string>
    dotnet run
  3. Run SignalR client.

    cd samples\Management\SignalRClient
    dotnet run

    Open the function logs in Azure portal and you’ll see a connected event is sent to the function:

    Azure Function output

    If you stop the client you’ll also see a disconnected event is received.

Try it now!

This feature is now in public preview so feel free to try it out and let us know your feedback by filing issues on Github.

For more information about how to use Event Grid with SignalR Service, you can read this article or try this sample.

Ken Chen

Principal Software Engineering Manager

Follow Ken   

Posted on Leave a comment

ASP.NET Core and Blazor updates in .NET Core 3.0 Preview 6

Daniel Roth


.NET Core 3.0 Preview 6 is now available and it includes a bunch of new updates to ASP.NET Core and Blazor.

Here’s the list of what’s new in this preview:

  • New Razor features: @attribute, @code, @key, @namespace, markup in @functions
  • Blazor directive attributes
  • Authentication & authorization support for Blazor apps
  • Static assets in Razor class libraries
  • Json.NET no longer referenced in project templates
  • Certificate and Kerberos Authentication
  • SignalR Auto-reconnect
  • Managed gRPC Client
  • gRPC Client Factory
  • gRPC Interceptors

Please see the release notes for additional details and known issues.

Get started

To get started with ASP.NET Core in .NET Core 3.0 Preview 6 install the .NET Core 3.0 Preview 6 SDK

If you’re on Windows using Visual Studio, you also need to install the latest preview of Visual Studio 2019.

For the latest client-side Blazor templates also install the latest Blazor extension from the Visual Studio Marketplace.

Upgrade an existing project

To upgrade an existing an ASP.NET Core app to .NET Core 3.0 Preview 6, follow the migrations steps in the ASP.NET Core docs.

Please also see the full list of breaking changes in ASP.NET Core 3.0.

To upgrade an existing ASP.NET Core 3.0 Preview 5 project to Preview 6:

  • Update Microsoft.AspNetCore.* package references to 3.0.0-preview6.19307.2
  • In Blazor apps:
    • Rename @functions to @code
    • Update Blazor specific attributes and event handlers to use the new directive attribute syntax (see below)
    • Remove any call to app.UseBlazor<TStartup>() and instead add a call to app.UseClientSideBlazorFiles<TStartup>() before the call to app.UseRouting(). Also add a call to endpoints.MapFallbackToClientSideBlazor<TStartup>("index.html") in the call to app.UseEndpoints().


app.UseRouting(); app.UseEndpoints(endpoints =>
{ endpoints.MapDefaultControllerRoute();
}); app.UseBlazor<Client.Startup>();


app.UseClientSideBlazorFiles<Client.Startup>(); app.UseRouting(); app.UseEndpoints(endpoints =>
{ endpoints.MapDefaultControllerRoute(); endpoints.MapFallbackToClientSideBlazor<Client.Startup>("index.html");

New Razor features

We’ve added support for the following new Razor language features in this release.


The new @attribute directive adds the specified attribute to the generated class.

@attribute [Authorize]


The new @code directive is used in .razor files (not supported in .cshtml files) to specify a code block to add to the generated class as additional members. It’s equivalent to @functions, but now with a better name.

@code { int currentCount = 0; void IncrementCount() { currentCount++; }


The new @key directive attribute is used in .razor files to specify a value (any object or unique identifier) that the Blazor diffing algorithm can use to preserve elements or components in a list.

@foreach (var flight in Flights) { }

To understand why this feature is needed, consider rendering a list of cards with flight details without this feature:

@foreach (var flight in Flights) { }

If you add a new flight into the middle of the Flights list the existing DetailsCard instances should remain unaffected and one new DetailsCard should be inserted into the rendered output.

To visualize this, if Flights previously contained [F0, F1, F2], then this is the before state:

  • DetailsCard0, with Flight=F0
  • DetailsCard1, with Flight=F1
  • DetailsCard2, with Flight=F2

… and this is the desired after state, given we insert a new item FNew at index 1:

  • DetailsCard0, with Flight=F0
  • DetailsCardNew, with Flight=FNew
  • DetailsCard1, with Flight=F1
  • DetailsCard2, with Flight=F2

However, the actual after state this:

  • DetailsCard0, with Flight=F0
  • DetailsCard1, with Flight=FNew
  • DetailsCard2, with Flight=F1
  • DetailsCardNew, with Flight=F2

The system has no way to know that DetailsCard2 or DetailsCard3 should preserve their associations with their older Flight instances, so it just re-associates them with whatever Flight matches their position in the list. As a result, DetailsCard1 and DetailsCard2 rebuild themselves completely using new data, which is wasteful and sometimes even leads to user-visible problems (e.g., input focus is unexpectedly lost).

By adding keys using @key the diffing algorithm can associate the old and new elements or components.


Specifies the namespace for the generated class or the namespace prefix when used in an _Imports.razor file. The @namespace directive works today in pages and views (.cshtml) apps, but is now it is also supported with components (.razor).

@namespace MyNamespace

Markup in @functions and local functions

In views and pages (.cshtml files) you can now add markup inside of methods in the @functions block and in local functions.

@{ GreetPerson(person); } @functions { void GreetPerson(Person person) { <p>Hello, <em>@person.Name!</em></p> }

Blazor directive attributes

Blazor uses a variety of attributes for influencing how components get compiled (e.g. ref, bind, event handlers, etc.). These attributes have been added organically to Blazor over time and use different syntaxes. In this Blazor release we’ve standardized on a common syntax for directive attributes. This makes the Razor syntax used by Blazor more consistent and predictable. It also paves the way for future extensibility.

Directive attributes all follow the following syntax where the values in parenthesis are optional:


Some valid examples:

<!-- directive -->
<!-- directive with key/value arg-->
<!-- directive with suffix -->
<!-- directive with suffix and key/value arg-->

All of the Blazor built-in directive attributes have been updated to use this new syntax as described below.

Event handlers

Specifying event handlers in Blazor now uses the new directive attribute syntax instead of the normal HTML syntax. The syntax is similar to the HTML syntax, but now with a leading @ character. This makes C# event handlers distinct from JS event handlers.

<button @onclick="@Clicked">Click me!</button>

When specifying a delegate for C# event handler the @ prefix is currently still required on the attribute value, but we expect to remove this requirement in a future update.

In the future we also expect to use the directive attribute syntax to support additional features for event handlers. For example, stopping event propagation will likely look something like this (not implemented yet, but it gives you an idea of scenarios now enabled by directive attributes):

<button @onclick="Clicked" @onclick:stopPropagation>Click me!</button>


<input @bind="myValue">...</input>
<input @bind="myValue" @bind:format="mm/dd">...</input>
<MyButton @bind-Value="myValue">...</MyButton>




<button @ref="myButton">...</button>

Authentication & authorization support for Blazor apps

Blazor now has built-in support for handling authentication and authorization. The server-side Blazor template now supports options for enabling all of the standard authentication configurations using ASP.NET Core Identity, Azure AD, and Azure AD B2C. We haven’t updated the Blazor WebAssembly templates to support these options yet, but we plan to do so after .NET Core 3.0 has shipped.

To create a new Blazor app with authentication enabled:

  1. Create a new Blazor (server-side) project and select the link to change the authentication configuration. For example, select “Individual User Accounts” and “Store user accounts in-app” to use Blazor with ASP.NET Core Identity:

    Blazor authentication

  2. Run the app. The app includes links in the top row for registering as a new user and logging in.

    Blazor authentication running

  3. Select the Register link to register a new user.

    Blazor authentication register

  4. Select “Apply Migrations” to apply the ASP.NET Core Identity migrations to the database.

    Blazor authentication apply migrations

  5. You should now be logged in.

    Blazor authentication logged in

  6. Select your user name to edit your user profile.

    Blazor authentication edit profile

In the Blazor app, authentication and authorization are configured in the Startup class using the standard ASP.NET Core middleware.

app.UseRouting(); app.UseAuthentication();
app.UseAuthorization(); app.UseEndpoints(endpoints =>
{ endpoints.MapControllers(); endpoints.MapBlazorHub(); endpoints.MapFallbackToPage("/_Host");

When using ASP.NET Core Identity all of the identity related UI concerns are handled by the framework provided default identity UI.

services.AddDefaultIdentity<IdentityUser>() .AddEntityFrameworkStores<ApplicationDbContext>();

The authentication related links in top row of the app are rendered using the new built-in AuthorizeView component, which displays different content depending on the authentication state.


<AuthorizeView> <Authorized> <a href="Identity/Account/Manage">Hello, @context.User.Identity.Name!</a> <a href="Identity/Account/LogOut">Log out</a> </Authorized> <NotAuthorized> <a href="Identity/Account/Register">Register</a> <a href="Identity/Account/Login">Log in</a> </NotAuthorized>

The AuthorizeView component will only display its child content when the user is authorized. Alternatively, the AuthorizeView takes parameters for specifying different templates when the user is Authorized, NotAuthorized, or Authorizing. The current authentication state is passed to these templates through the implicit context parameter. You can also specify specific roles or an authorization policy on the AuthorizeView that the user must satisfy to see the authorized view.

To authorize access to specific pages in a Blazor app, use the normal [Authorize] attribute. You can apply the [Authorize] attribute to a component using the new @attribute directive.

@using Microsoft.AspNetCore.Authorization
@attribute [Authorize]
@page "/fetchdata"

To specify what content to display on a page that requires authorization when the user isn’t authorized or is still in the processing of authorizing, use the NotAuthorizedContent and AuthorizingContent parameters on the Router component. These Router parameters are only support in client-side Blazor for this release, but they will be enabled for server-side Blazor in a future update.

The new AuthenticationStateProvider service make the authentication state available to Blazor apps in a uniform way whether they run on the server or client-side in the browser. In server-side Blazor apps the AuthenticationStateProvider surfaces the user from the HttpContext that established the connection to the server. Client-side Blazor apps can configure a custom AuthenticationStateProvider as appropriate for that application. For example, it might retrieve the current user information by querying an endpoint on the server.

The authentication state is made available to the app as a cascading value (Task<AuthenticationState>) using the CascadingAuthenticationState component. This cascading value is then used by the AuthorizeView and Router components to authorize access to specific parts of the UI.


<CascadingAuthenticationState> <Router AppAssembly="typeof(Startup).Assembly"> <NotFoundContent> <p>Sorry, there's nothing at this address.</p> </NotFoundContent> </Router>

Static assets in Razor class libraries

Razor class libraries can now include static assets like JavaScript, CSS, and images. These static assets can then be included in ASP.NET Core apps by referencing the Razor class library project or via a package reference.

To include static assets in a Razor class library add a wwwroot folder to the Razor class library and include any required files in that folder.

When a Razor class library with static assets is referenced either as a project reference or as a package, the static assets from the library are made available to the app under the path prefix _content/{LIBRARY NAME}/. The static assets stay in their original folders and any changes to the content of static assets in the Razor class libraries are reflected in the app without rebuilding.

When the app is published, the companion assets from all referenced Razor class libraries are copied into the wwwroot folder of the published app under the same prefix.

To try out using static assets from a Razor class library:

  1. Create a default ASP.NET Core Web App.

    dotnet new webapp -o WebApp1
  2. Create a Razor class library and reference it from the web app.

    dotnet new razorclasslib -o RazorLib1
    dotnet add WebApp1 reference RazorLib1
  3. Add a wwwroot folder to the Razor class library and include a JavaScript file that logs a simple message to the console.

    cd RazorLib1
    mkdir wwwroot


    console.log("Hello from RazorLib1!");
  4. Reference the script file from Index.cshtml in the web app.

  5. Run the app and look for the output in the browser console.

    Hello from RazorLib1!

Projects now use System.Text.Json by default

New ASP.NET Core projects will now use System.Text.Json for JSON handling by default. In this release we removed Json.NET (Newtonsoft.Json) from the project templates. To enable support for using Json.NET, add the Microsoft.AspNetCore.Mvc.NewtonsoftJson package to your project and add a call to AddNewtonsoftJson() following code in your Startup.ConfigureServices method. For example:

services.AddMvc() .AddNewtonsoftJson();

Certificate and Kerberos authentication

Preview 6 brings Certificate and Kerberos authentication to ASP.NET Core.

Certificate authentication requires you to configure your server to accept certificates, and then add the authentication middleware in Startup.Configure and the certificate authentication service in Startup.ConfigureServices.

public void ConfigureServices(IServiceCollection services)
{ services.AddAuthentication( CertificateAuthenticationDefaults.AuthenticationScheme) .AddCertificate(); // All the other service configuration.
} public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{ app.UseAuthentication(); // All the other app configuration.

Options for certificate authentication include the ability to accept self-signed certificates, check for certificate revocation, and check that the proffered certificate has the right usage flags in it. A default user principal is constructed from the certificate properties, with an event that enables you to supplement or replace the principal. All the options, and instructions on how to configure common hosts for certificate authentication can be found in the documentation.

We’ve also extended “Windows Authentication” onto Linux and macOS. Previously this authentication type was limited to IIS and HttpSys, but now Kestrel has the ability to use Negotiate, Kerberos, and NTLM on Windows, Linux, and macOS for Windows domain joined hosts by using the Microsoft.AspNetCore.Authentication.Negotiate nuget package. As with the other authentication services you configure authentication app wide, then configure the service:

public void ConfigureServices(IServiceCollection services)
{ services.AddAuthentication(NegotiateDefaults.AuthenticationScheme) .AddNegotiate();
} public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{ app.UseAuthentication(); // All the other app configuration.

Your host must be configured correctly. Windows hosts must have SPNs added to the user account hosting the application. Linux and macOS machines must be joined to the domain, then SPNs must be created for the web process, as well as keytab files generated and configured on the host machine. Full instructions are given in the documentation.

SignalR Auto-reconnect

This preview release, available now via npm install @aspnet/signalr@next and in the .NET Core SignalR Client, includes a new automatic reconnection feature. With this release we’ve added the withAutomaticReconnect() method to the HubConnectionBuilder. By default, the client will try to reconnect immediately and after 2, 10, and 30 seconds. Enlisting in automatic reconnect is opt-in, but simple via this new method.

const connection = new signalR.HubConnectionBuilder() .withUrl("/chatHub") .withAutomaticReconnect() .build();

By passing an array of millisecond-based durations to the method, you can be very granular about how your reconnection attempts occur over time.

.withAutomaticReconnect([0, 3000, 5000, 10000, 15000, 30000])
//.withAutomaticReconnect([0, 2000, 10000, 30000]) yields the default behavior

Or you can pass in an implementation of a custom reconnect policy that gives you full control.

If the reconnection fails after the 30-second point (or whatever you’ve set as your maximum), the client presumes the connection is offline and stops trying to reconnect. During these reconnection attempts you’ll want to update your application UI to provide cues to the user that the reconnection is being attempted.

Reconnection Event Handlers

To make this easier, we’ve expanded the SignalR client API to include onreconnecting and onreconnected event handlers. The first of these handlers, onreconnecting, gives developers a good opportunity to disable UI or to let users know the app is offline.

connection.onreconnecting((error) => { const status = `Connection lost due to error "${error}". Reconnecting.`; document.getElementById("messageInput").disabled = true; document.getElementById("sendButton").disabled = true; document.getElementById("connectionStatus").innerText = status;

Likewise, the onreconnected handler gives developers an opportunity to update the UI once the connection is reestablished.

connection.onreconnected((connectionId) => { const status = `Connection reestablished. Connected.`; document.getElementById("messageInput").disabled = false; document.getElementById("sendButton").disabled = false; document.getElementById("connectionStatus").innerText = status;

Learn more about customizing and handling reconnection

Automatic reconnect has been partially documented already in the preview release. Check out the deeper docs on the topic, with more examples and details on usage, at

Managed gRPC Client

In prior previews, we relied on the Grpc.Core library for client support. The addition of HTTP/2 support in HttpClient in this preview has allowed us to introduce a fully managed gRPC client.

To begin using the new client, add a package reference to Grpc.Net.Client and then you can create a new client.

var httpClient = new HttpClient() { BaseAddress = new Uri("https://localhost:5001") };
var client = GrpcClient.Create<GreeterClient>(httpClient);

gRPC Client Factory

Building on the opinionated pattern we introduced in HttpClientFactory, we’ve added a gRPC client factory for creating gRPC client instances in your project. There are two flavors of the factory that we’ve added: Grpc.Net.ClientFactory and Grpc.AspNetCore.Server.ClientFactory.

The Grpc.Net.ClientFactory is designed for use in non-ASP.NET app models (such as Worker Services) that still use the Microsoft.Extensions.* primitives without a dependency on ASP.NET Core.

In applications that perform service-to-service communication, we often observe that most servers are also clients that consume other services. In these scenarios, we recommend the use of Grpc.AspNetCore.Server.ClientFactory which features automatic propagation of gRPC deadlines and cancellation tokens.

To use the client factory, add the appropriate package reference to your project (Grpc.AspNetCore.Server.Factory or Grpc.Net.ClientFactory) before adding the following code to ConfigureServices().

services .AddGrpcClient<GreeterClient>(options => { options.BaseAddress = new Uri("https://localhost:5001"); });

gRPC Interceptors

gRPC exposes a mechanism to intercept RPC invocations on both the client and the server. Interceptors can be used in conjunction with existing HTTP middleware. Unlike HTTP middleware, interceptors give you access to actual request/response objects before serialization (on the client) and after deserialization (on the server) and vice versa for the response. All middlewares run before interceptors on the request side and vice versa on the response side.

Client interceptors

When used in conjunction with the client factory, you can add a client interceptor as shown below.

services .AddGrpcClient<GreeterClient>(options => { options.BaseAddress = new Uri("https://localhost:5001"); }) .AddInterceptor<CallbackInterceptor>();

Server interceptors

Server interceptors can be registered in ConfigureServices() as shown below.

services .AddGrpc(options => { // This registers a global interceptor options.Interceptors.Add<MaxStreamingRequestTimeoutInterceptor>(TimeSpan.FromSeconds(30)); }) .AddServiceOptions<GreeterService>(options => { // This registers an interceptor for the Greeter service options.Interceptors.Add<UnaryCachingInterceptor>(); });

For examples on how to author an interceptors, take a look at these examples in the grpc-dotnet repo.

Give feedback

We hope you enjoy the new features in this preview release of ASP.NET Core and Blazor! Please let us know what you think by filing issues on GitHub.

Thanks for trying out ASP.NET Core and Blazor!

Daniel Roth
Daniel Roth

Principal Program Manager, ASP.NET

Follow Daniel   

Posted on Leave a comment

What’s new in Azure SignalR 1.1.0 Preview 1



We just shipped 1.1.0 Preview 1 of Azure SignalR Service SDK to support some new features in ASP.NET Core 3.0, including endpoint routing and server-side Blazor. Let’s take a look how you can use them in your Azure SignalR application.

Here is the list of what’s new in this release:

  • Endpoint routing support for ASP.NET Core 3
  • Use SignalR service in server-side Blazor apps
  • Server stickiness

Endpoint routing support for ASP.NET Core 3

For those who are using Azure SignalR, you should be familiar with AddAzureSignalR() and UseAzureSignalR(). These two methods are required if you want to switch your app server from self-hosted SignalR to use Azure SignalR.

A typical Azure SignalR application usually looks like this in Startup.cs (note where AddAzureSignalR() and UseAzureSignalR() are used):

public void ConfigureServices(IServiceCollection services)
{ ... services.AddSignalR() .AddAzureSignalR(); ...
} public void Configure(IApplicationBuilder app)
{ ... app.UseAzureSignalR(routes => { routes.MapHub<Chat>("/chat"); }); ...

ASP.NET Core 3.0 introduced a new endpoint routing support which allows routable things like MVC and SignalR to be mixed together in a unified UseEndpoints() interface.

For example, you can call MapGet() and MapHub() in a single UseEndpoints() call, like this:

app.UseEndpoints(routes =>
{ routes.MapGet("/foo", async context => { await context.Response.WriteAsync("bar"); }); routes.MapHub<Chat>("/chat");

This new syntax is also supported in the latest Azure SignalR SDK so you don’t need to use a separate UseAzureSignalR() to map hubs.

Now your Azure SignalR application looks like this:

public void ConfigureServices(IServiceCollection services)
{ ... services.AddSignalR() .AddAzureSignalR(); ...
} public void Configure(IApplicationBuilder app)
{ ... app.UseRouting(); app.UseEndpoints(routes => { routes.MapHub<Chat>("/chat"); }); ...

The only change you need to make is to call AddAzureSignalR() after AddSignalR().

This will be very useful in the case that SignalR is deeply integrated in your code base or the library you’re using. For example, when you’re using server-side Blazor.

Use SignalR service in server-side Blazor apps

Server-side Blazor is a new way to build interactive client-side web UI in ASP.NET Core 3. In server-side Blazor, UI updates are rendered at server side, then sent to browser through a SignalR connection. Since it uses SignalR, there is a natural need to use Azure SignalR service to handle the SignalR traffic so your application can easily scale.


If you look at some server-side Blazor code samples, you’ll see they have a call to MapBlazorHub() to setup the communication channel between client and server.

app.UseEndpoints(endpoints =>
{ ... endpoints.MapBlazorHub(); ...

The implementation of this method calls MapHub() to create a SignalR hub at server side. Before this release there is no way to change the implementation of MapBlazorHub() to use SignalR service. Now if you call AddAzureSignalR(), MapBlazorHub() will also use SignalR service to host the hub instead of hosting it on the server.

Please follow these steps to change your server-side Blazor app to use SignalR service:

  1. Open your Startup.cs, add services.AddSignalR().AddAzureSignalR() in ConfigureServices().
  2. Create a new SignalR service instance.
  3. Get connection string and set it to environment variable Azure:SignalR:ConnectionString.

Then run your app you’ll see the WebSocket connection is going through SignalR service.

Check out this repo for a complete code sample.

Server stickiness

The typical connection flow when using SignalR service is that client first negotiates with app server to get the url of SignalR service, then service routes client to app server.

When you have multiple app servers, there is no guarantee that two servers (the one who does negotiation and the one who gets the hub invocation) will be the same one.

We hear a lot of customers asking about whether it’s possible to make the two servers the same one so they can share some states between negotiation and hub invocation. In this release we have added a new “server sticky mode” to support this scenario.

To enable this, you just need to set ServerStickyMode to Required in AddAzureSignalR():

services.AddSignalR().AddAzureSignalR(options => { options.ServerStickyMode = ServerStickyMode.Required;

Now for any connection, SignalR service will guarantee negotiation and hub invocation go to the same app server (called “server sticky”).

This feature is very useful when you have client state information maintained locally on the app server. For example, when using server-side Blazor, UI state is maintained at server side so you want all client requests go to the same server including the SignalR connection. So you need to set server sticky mode to Required when using server-side Blazor together with SignalR service.

Please note in this mode, there may be additional cost for the service to route connection to the right app server. So there may be some negative impact in message latency. If you don’t want the performance penalty, there is another Preferred mode you can use. In this mode stickiness is not always guaranteed (only when there is no additional cost to do the routing). But you can still gain some performance benefits as message delivery is more efficient if sender and receiver are on the same app server. Also when sticky mode is enabled, service won’t balance connections between app servers (by default SignalR service balances the traffic by routing to a server with least connections). So we recommend to set sticky mode to Disabled (this is also the default value) and only enable it when there is a need.

You can refer to this doc for more details about server sticky mode.

Ken Chen

Principal Software Engineering Manager

Follow Ken   

Posted on Leave a comment

Azure SignalR Service now supports ASP.NET!



We’ve just shipped the official version of the SignalR Service SDK for ASP.NET support:

Azure SignalR Service is a fully managed Azure service for real-time messaging. It is a preferred way for scaling ASP.NET Core SignalR application. However, SignalR Service is based on SignalR for ASP.NET Core 2.0, which is not 100% compatible with ASP.NET SignalR. Some code changes and proper version of dependent libraries are needed to make ASP.NET SignalR application work with SignalR Service.

We have received many usage feedbacks from customers since we announced the preview support for ASP.NET, at Microsoft Ignite 2018. Today, we are excited to announce that we have released the generally available version 1.0.0 of ASP.NET support SDK for Azure SignalR Service!

This diagram shows the typical architecture to use Azure SignalR Service with application server either written in ASP.NET Core, or now, in ASP.NET.


For self-hosted SignalR application, the application server listens to and serves client connections directly. With SignalR Service, the application server will only respond to clients’ negotiate requests, and redirect clients to SignalR Service to establish the persistent client-server connections.

Using the ASP.NET support for Azure SignalR Service you will be able to:

  • Continue to keep SignalR application using ASP.NET, but work with fully managed ASP.NET Core based SignalR Service.
  • Change a few lines of SignalR API codes, to switch to use SignalR Service instead of self-hosted SignalR Hubs.
  • Leverage Azure SignalR Service’s built-in features and tools to help operate the SignalR application, with guaranteed SLA.

To receive the full benefit from the new ASP.NET support feature, please download and upgrade your SDKs to the latest supported versions:

  • .NET: 4.6.1+
  • Microsoft.AspNet.SignalR.*: 2.4.1
  • Microsoft.Azure.SignalR.AspNet: 1.0.0

Many factors, including non-technical ones, make the web application migrate from ASP.NET to ASP.NET Core difficult.

The ASP.NET support for Azure SignalR Service is to enable ASP.NET SignalR application developers to easily switch to use SignalR Service with minimal code change.

Some APIs and features are no longer supported:

  • Automatic reconnects
  • Forever Frame transport
  • HubState
  • PersistentConnection class
  • GlobalHost object
  • HubPipeline module
  • Client side Internet Explorer support before Microsoft Internet Explorer 11

ASP.NET support is focus on compatibility, so not all ASP.NET Core SignalR new features are supported. To name a few: MessagePack, Streaming, etc., are only available for ASP.NET Core SignalR applications.

SignalR Service can be configured for different service mode: Classic/Default/Serverless. For ASP.NET support, the Serverless mode is not supported.

For a complete list of feature comparison between ASP.NET SignalR and ASP.NET Core SignalR, the proper version of SDKs to use in each case, and what are the recommended alternatives to use for features discontinued in ASP.NET Core SignalR, please refer to doc here.

We’d like to hear about your feedback and comments. You can reach the product team at the GitHub repo, or by email.

Zhidi Shang

Principal Program Manager, Azure SignalR Service

Follow Zhidi   

Posted on Leave a comment

ASP.NET Core updates in .NET Core 3.0 Preview 4

Daniel Roth


.NET Core 3.0 Preview 4 is now available and it includes a bunch of new updates to ASP.NET Core.

Here’s the list of what’s new in this preview:

  • Razor Components renamed back to server-side Blazor
  • Client-side Blazor on WebAssembly now in official preview
  • Resolve components based on @using
  • _Imports.razor
  • New component item template
  • Reconnection to the same server
  • Stateful reconnection after prerendering
  • Render stateful interactive components from Razor pages and views
  • Detect when the app is prerendering
  • Configure the SignalR client for server-side Blazor apps
  • Improved SignalR reconnect features
  • Configure SignalR client for server-side Blazor apps
  • Additional options for MVC service registration
  • Endpoint routing updates
  • New template for gRPC
  • Design-time build for gRPC
  • New Worker SDK

Please see the release notes for additional details and known issues.

Get started

To get started with ASP.NET Core in .NET Core 3.0 Preview 4 install the .NET Core 3.0 Preview 4 SDK

If you’re on Windows using Visual Studio, you also need to install the latest preview of Visual Studio 2019.

If you’re using Visual Studio Code, check out the improved Razor tooling and Blazor support in the C# extension.

Upgrade an existing project

To upgrade an existing an ASP.NET Core app to .NET Core 3.0 Preview 4, follow the migrations steps in the ASP.NET Core docs.

Please also see the full list of breaking changes in ASP.NET Core 3.0.

To upgrade an existing ASP.NET Core 3.0 Preview 3 project to Preview 4:

  • Update Microsoft.AspNetCore.* package references to 3.0.0-preview4-19216-03
  • In Razor Components apps (i.e. server-side Blazor apps) rename _ViewImports.cshtml to _Imports.razor for Razor imports that should apply to Razor components.
  • In Razor Component apps, in your Index.cshtml file, change the tag that references components.server.js so that it references blazor.server.js instead.
  • Remove any use of the _RazorComponentInclude property in your project file and rename and component files using the .cshtml file extension to use the .razor file extension instead.
  • Remove package references to Microsoft.AspNetCore.Components.Server.
  • Replace calls to AddRazorComponents in Startup.ConfigureServices with AddServerSideBlazor.
  • Replace calls to MapComponentHub with MapBlazorHub.
  • Remove any use of the Microsoft.AspNetCore.Components.Services namespace and replace with Microsoft.AspNetCore.Components as required.
  • In Razor Component apps, replace the {*clientPath} route in the host Razor Page with “/” and add a call to MapFallbackToPage in UseEndpoints.
  • Update any call to UseRouting in your Startup.Configure method to move the route mapping logic into a call to UseEndpoints at the point where you want the endpoints to be executed.


app.UseRouting(routes =>
{ routes.MapRazorPages();
}); app.UseCookiePolicy(); app.UseAuthorization();


app.UseRouting(); app.UseCookiePolicy(); app.UseAuthorization(); app.UseEndpoints(routes =>
{ routes.MapRazorPages(); routes.MapFallbackToPage();

Razor Components renamed back to server-side Blazor

For a while, we’ve used the terminology Razor Components in some cases, and Blazor in other cases. This has proven to be confusing, so following a lot of community feedback, we’ve decided to drop the name ASP.NET Core Razor Components, and return to the name Server-side Blazor instead.

This emphasizes that Blazor is a single client app model with multiple hosting models:

  • Server-side Blazor runs on the server via SignalR
  • Client-side Blazor runs client-side on WebAssembly

… but either way, it’s the same programming model. The same Blazor components can be hosted in both environments.

In this preview of the .NET Core SDK we renamed the “Razor Components” template back to “Blazor (server-side)” and updated the related APIs accordingly. In Visual Studio the template will still show up as “Razor Components” when using Visual Studio 2019 16.1.0 Preview 1, but it will start showing up as “Blazor (server-side)” in a subsequent preview. We’ve also updated the template to use the new super cool flaming purple Blazor icon.

Blazor (server-side) template

Client-side Blazor on WebAssembly now in official preview

We’re also thrilled to announce that client-side Blazor on WebAssembly is now in official preview! Blazor is no longer experimental and we are committing to ship it as a supported web UI framework including support for running client-side in the browser on WebAssembly.

  • Server-side Blazor will ship as part of .NET Core 3.0. This was already announced last October.
  • Client-side Blazor won’t ship as part of the initial .NET Core 3.0 release, but we are now announcing it is committed to ship as part of a future .NET Core release (and hence is no longer an “experiment”).

With each preview release of .NET Core 3.0, we will continue to ship preview releases of both server and client-side Blazor.

Resolve components based on @using

Components in referenced assemblies are now always in scope and can be specified using their full type name including the namespace. You no longer need to import components from component libraries using the @addTagHelper directive.

For example, you can add a Counter component to the Index page like this:

Use the @using directive to bring component namespaces into scope just like you would in C# code:

@using BlazorWebApp1.Pages 


Use _Imports.razor files to import Razor directives across multiple Razor component files (.razor) in a hierarchical fashion.

For example, the following _Imports.razor file applies a layout and adds using statements for all Razor components in a the same folder and in any sub folders:

@layout MainLayout
@using Microsoft.AspNetCore.Components.
@using BlazorApp1.Data

This is similar to how you can use _ViewImports.cshtml with Razor views and pages, but applied specifically to Razor component files.

New component item template

You can now add components to Blazor apps using the new Razor Component item template:

dotnet new razorcomponent -n MyComponent1

Reconnection to the same server

Server-side Blazor apps require an active SignalR connection to the server to function. In this preview, the app will now attempt to reconnect to the server. As long as the state for that client is still in memory, the client session will resume without losing any state.

When the client detects that the connection has been lost a default UI is displayed to the user while the client attempts to reconnect:

Attempting reconnect

If reconnection failed the user is given the option to retry:

Reconnect failed

To customize this UI define an element with components-reconnect-modal as its ID. The client will update this element with one of the following CSS classes based on the state of the connection:

  • components-reconnect-show: Show the UI to indicate the connection was lost and the client is attempting to reconnect.
  • components-reconnect-hide: The client has an active connection – hide the UI.
  • components-reconnect-failed: Reconnection failed. To attempt reconnection again call window.Blazor.reconnect().

Stateful reconnection after prerendering

Server-side Blazor apps are setup by default to prerender the UI on the server before client connection back to the server is established. This is setup in the _Host.cshtml Razor page:

 @(await Html.RenderComponentAsync()) 

In this preview the client will now reconnect back to the server to the same state that was used to prerender the app. If the app state is still in memory it doesn’t need to be rerendered once the SignalR connection is established.

Render stateful interactive components from Razor pages and views

You can now add stateful interactive components to a Razor page or View. When the page or view renders the component will be prerendered with it. The app will then reconnect to the component state once the client connection has been established as long as it is still in memory.

For example, the following Razor page renders a Counter component with an initial count that is specified using a form:

<h1>My Razor Page</h1>
<form> <input type="number" asp-for="InitialCount" /> <button type="submit">Set initial count</button>
</form> @(await Html.RenderComponentAsync<Counter>(new { InitialCount = InitialCount })) @functions { [BindProperty(SupportsGet=true)] public int InitialCount { get; set; }

Interactive component on Razor page

Detect when the app is prerendering

While a Blazor app is prerendering, certain actions (like calling into JavaScript) are not possible because a connection with the browser has not yet been established. Components may need to render differently when being prerendered.

To delay JavaScript interop calls until after the connection with the browser has been established you can now use the OnAfterRenderAsync component lifecycle event. This event will only be called after the app has been fully rendered and the client connection established.

To conditionally render different content based on whether the app is currently being prerendered or not use IsConnected property on the IComponentContext service. This property will only return true if there is an active connection with the client.

Configure the SignalR client for server-side Blazor apps

Sometimes you need to configure the SignalR client used by server-side Blazor apps. For example, you might want to configure logging on the SignalR client to diagnose a connection issue.

To configure the SignalR client for server-side Blazor apps, add an autostart="false" attribute on the script tag for the blazor.server.js script, and then call Blazor.start passing in a config object that specifies the SignalR builder:

 Blazor.start({ configureSignalR: function (builder) { builder.configureLogging(2); // LogLevel.Information } });

Improved SignalR connection lifetime handling

Preview 4 will improve the developer experience for handling SignalR disconnection and reconnection. Automatic reconnects can be enabled by calling the withAutomaticReconnect method on HubConnectionBuilder:

const connection = new signalR.HubConnectionBuilder() .withUrl("/chatHub") .withAutomaticReconnect() .build();

Without any parameters, withAutomaticReconnect() will cause the configure the client to try to reconnect, waiting 0, 2, 10 and 30 seconds respectively before between each attempt.

In order to configure a non-default number of reconnect attempts before failure, or to change the reconnect timing, withAutomaticReconnect accepts an array of numbers representing the delay in milliseconds to wait before starting each reconnect attempt.

const connection = new signalR.HubConnectionBuilder() .withUrl("/chatHub") .withAutomaticReconnect([0, 0, 2000, 5000]) // defaults to [0, 2000, 10000, 30000] .build();

Improved disconnect & reconnect handling opportunities

Before starting any reconnect attempts, the HubConnection will transition to the Reconnecting state and fire its onreconnecting callback. This provides an opportunity to warn users that the connection has been lost, disable UI elements, and mitigate confusing user scenarios that might occur due to the disconnected state.

connection.onreconnecting((error) => { console.assert(connection.state === signalR.HubConnectionState.Reconnecting); document.getElementById("messageInput").disabled = true; const li = document.createElement("li"); li.textContent = `Connection lost due to error "${error}". Reconnecting.`; document.getElementById("messagesList").appendChild(li);

If the client successfully reconnects within its first four attempts, the HubConnection will transition back to the Connected state and fire onreconnected callbacks. This gives developers a good opportunity to inform users the connection has been reestablished.

connection.onreconnected((connectionId) => { console.assert(connection.state === signalR.HubConnectionState.Connected); document.getElementById("messageInput").disabled = false; const li = document.createElement("li"); li.textContent = `Connection reestablished. Connected with connectionId "${connectionId}".`; document.getElementById("messagesList").appendChild(li);

If the client doesn’t successfully reconnect within its first four attempts, the HubConnection will transition to the Disconnected state and fire its onclosed callbacks. This is a good opportunity to inform users the connection has been permanently lost and recommend refreshing the page.

connection.onclose((error) => { console.assert(connection.state === signalR.HubConnectionState.Disconnected); document.getElementById("messageInput").disabled = true; const li = document.createElement("li"); li.textContent = `Connection closed due to error "${error}". Try refreshing this page to restart the connection.`; document.getElementById("messagesList").appendChild(li);

Additional options for MVC service registration

We’re adding some new options for registering MVC’s various features inside ConfigureServices.

What’s changing

We’re adding three new top level extension methods related to MVC features on IServiceCollection. Along with this change we are updating our templates to use these new methods instead of AddMvc().

AddMvc() is not being removed and will continue to behave as it does today.

public void ConfigureServices(IServiceCollection services)
{ // Adds support for controllers and API-related features - but not views or pages. // // Used by the API template. services.AddControllers();
public void ConfigureServices(IServiceCollection services)
{ // Adds support for controllers, API-related features, and views - but not pages. // // Used by the Web Application (MVC) template. services.AddControllersWithViews();
public void ConfigureServices(IServiceCollection services)
{ // Adds support for Razor Pages and minimal controller support. // // Used by the Web Application template. services.AddRazorPages();

These new methods can also be combined. This example is equivalent to the current AddMvc().

public void ConfigureServices(IServiceCollection services)
{ services.AddControllers(); services.AddRazorPages();

These methods return an IMvcBuilder that can be chained to access any of the methods that are available today from the builder returned by AddMvc().

We recommend using whichever option feels best based on your needs.


We wanted to provide some more options that represent how users use the product. In particular we’ve received strong feedback from users that want an API-focused flavor of MVC without the overhead for having the ability to serve views and pages. We tried to provide an experience for this in the past through the AddMvcCore() method, but that approach hasn’t been very successful. Users who tried using AddMvcCore() have been surprised by how much they need to know to use it successfully, and as a result we haven’t promoted its usage. We hope that AddControllers() will better satisfy this scenario.

In addition to the AddControllers() experience, we’re also attempting to create options that feel right for other scenarios. We’ve heard requests for this in the past, but not as strongly as the requests for an API-focused profile. Your feedback about whether AddMvc() could be improved upon, and how will be valuable.

What’s in AddControllers()

AddControllers() includes support for:

  • Controllers
  • Model Binding
  • API Explorer (OpenAPI integration)
  • Authorization [Authorize]
  • CORS [EnableCors]
  • Data Annotations validation [Required]
  • Formatter Mappings (translate a file-extension to a content-type)

All of these features are included because they fit under the API-focused banner, and they are very much pay-for-play. None of these features proactively interact with the request pipeline, these are activated by attributes on your controller or model class. API Explorer is an slight exception, it is a piece of infrastructure used by OpenAPI libraries and will do nothing without Swashbuckle or NSwag.

Some notable features AddMvc() includes but AddControllers() does not:

  • Antiforgery
  • Temp Data
  • Views
  • Pages
  • Tag Helpers
  • Memory Cache

These features are view-related and aren’t necessary in an API-focused profile of MVC.

What’s in AddControllersWithViews()

AddControllersWithViews() includes support for:

  • Controllers
  • Model Binding
  • API Explorer (OpenAPI integration)
  • Authorization [Authorize]
  • CORS [EnableCors]
  • Data Annotations validation [Required]
  • Formatter Mappings (translate a file-extension to a content-type)
  • Antiforgery
  • Temp Data
  • Views
  • Tag Helpers
  • Memory Cache

We wanted to position AddControllersWithViews() as a superset of AddControllers() for simplicity in explaining it. This features set also happens to align with the ASP.NET Core 1.X release (before Razor Pages).

Some notable features AddMvc() includes but AddControllersWithViews() does not:
– Pages

What’s in AddRazorPages()

AddRazorPages() includes support for:

  • Pages
  • Controllers
  • Model Binding
  • Authorization [Authorize]
  • Data Annotations validation [Required]
  • Antiforgery
  • Temp Data
  • Views
  • Tag Helpers
  • Memory Cache

For now this profile includes basic support for controllers, but excludes many of the API-focused features listed below. We’re interested in your feedback about what should be included by default in AddRazorPages().

Some notable features AddMvc() includes but AddRazorPages() does not:

  • API Explorer (OpenAPI integration)
  • CORS [EnableCors]
  • Formatter Mappings (translate a file-extension to a content-type)

Endpoint Routing updates

In ASP.NET Core 2.2 we introduced a new routing implementation called Endpoint Routing which replaces IRouter-based routing for ASP.NET Core MVC. In the upcoming 3.0 release Endpoint Routing will become central to the ASP.NET Core middleware programming model. Endpoint Routing is designed to support greater interoperability between frameworks that need routing (MVC, gRPC, SignalR, and more …) and middleware that want to understand the decisions made by routing (localization, authorization, CORS, and more …).

While it’s still possible to use the old UseMvc() or UseRouter() middleware in a 3.0 application, we recommend that every application migrate to Endpoint Routing if possible. We are taking steps to address compatibility bugs and fill in previously unsupported scenarios. We welcome your feedback about what features are missing or anything else that’s not great about routing in this preview release.

We’ll be uploading another post soon with a conceptual overview and cookbook for Endpoint Routing in 3.0.

Endpoint Routing overview

Endpoint Routing is made up of the pair of middleware created by app.UseRouting() and app.UseEndpoints(). app.UseRouting() marks the position in the middleware pipeline where a routing decision is made – where an endpoint is selected. app.UseEndpoints() marks the position in the middleware pipeline where the selected endpoint is executed. Middleware that run in between these can see the selected endpoint (if any) or can select a different endpoint.

If you’re familiar with routing from using MVC then most of what you have experienced so far will behave the same way. Endpoint Routing understands the same route template syntax and processes URLs in a very similar way to the in-the-box implementations of IRouter. Endpoint routing supports the [Route] and similar attributes inside MVC.

We expect most applications will only require changes to the Startup.cs file.

A typical Configure() method using Endpoint Routing has the following high-level structure:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{ // Middleware that run before routing. Usually the following appear here: if (env.IsDevelopment()) { app.UseDeveloperExceptionPage(); app.UseDatabaseErrorPage(); } else { app.UseExceptionHandler("/Error"); } app.UseStaticFiles() // Runs matching. An endpoint is selected and set on the HttpContext if a match is found. app.UseRouting(); // Middleware that run after routing occurs. Usually the following appear here: app.UseAuthentication() app.UseAuthorization() app.UseCors() // These middleware can take different actions based on the endpoint. // Executes the endpoint that was selected by routing. app.UseEndpoints(endpoints => { // Mapping of endpoints goes here: endpoints.MapControllers() endpoints.MapRazorPages() endpoints.MapHub<MyChatHub>() endpoints.MapGrpcService<MyCalculatorService>() }); // Middleware here will only run if nothing was matched.

MVC Controllers, Razor Pages, SignalR, gRPC, and more are added inside UseEndpoints() – they are now part of the same routing system.

New template for gRPC

The gRPC template has been simplified to a single project template. We no longer include a gRPC client as part of the template.
For instructions on how to create a gRPC client, refer to the docs.

├── appsettings.Development.json
├── appsettings.json
├── grpc.csproj
├── Program.cs
├── Properties
│   └── launchSettings.json
├── Protos
│   └── greet.proto
├── Services
│   └── GreeterService.cs
└── Startup.cs 3 directories, 8 files

Design-time build for gRPC

Design-time build support for gRPC code-generation makes it easier to rapidly iterate on your gRPC services. Changes to your *.proto files no longer require you to build your project to re-run code generation.

Design time build

Worker SDK

In Preview 3 we introduced the new Worker Service template. In Preview 4 we’ve further decoupled that template from Web by introducing its own SDK. If you create a new Worker Service your csproj will now look like the following:

<Project Sdk="Microsoft.NET.Sdk.Worker"> <PropertyGroup> <TargetFramework>netcoreapp3.0</TargetFramework> <UserSecretsId>dotnet-WebApplication59-A2B1DB8D-0408-4583-80BA-1B32DAE36B97</UserSecretsId> </PropertyGroup> <ItemGroup> <PackageReference Include="Microsoft.Extensions.Hosting" Version="3.0.0-preview4.19216.2" /> </ItemGroup>

We’ll have more to share on the new Worker SDK in a future post.

Give feedback

We hope you enjoy the new features in this preview release of ASP.NET Core! Please let us know what you think by filing issues on GitHub.

Daniel Roth
Daniel Roth

Principal Program Manager, ASP.NET

Follow Daniel   

Posted on Leave a comment

ASP.NET Core updates in .NET Core 3.0 Preview 3

Daniel Roth


.NET Core 3.0 Preview 3 is now available and it includes a bunch of new updates to ASP.NET Core.

Here’s the list of what’s new in this preview:

  • Razor Components improvements:
    • Single project template
    • New .razor extension
    • Endpoint routing integration
    • Prerendering
    • Razor Components in Razor Class Libraries
    • Improved event handling
    • Forms & validation
  • Runtime compilation
  • Worker Service template
  • gRPC template
  • Angular template updated to Angular 7
  • Authentication for Single Page Applications
  • SignalR integration with endpoint routing
  • SignalR Java client support for long polling

Please see the release notes for additional details and known issues.

Get started

To get started with ASP.NET Core in .NET Core 3.0 Preview 3 install the .NET Core 3.0 Preview 3 SDK

If you’re on Windows using Visual Studio, you’ll also want to install the latest preview of Visual Studio 2019.

  • Note: To use use this preview of .NET Core 3.0 with the release channel of Visual Studio 2019, you will need to enable the option to use previews of the .NET Core SDK by going to Tools > Options > Projects and Solutions > .NET Core > Use previews of the .NET Core SDK

Upgrade an existing project

To upgrade an existing an ASP.NET Core app to .NET Core 3.0 Preview 3, follow the migrations steps in the ASP.NET Core docs.

Please also see the full list of breaking changes in ASP.NET Core 3.0.

Razor Components improvements

In the previous preview, we introduced Razor Components as a new way to build interactive client-side web UI with ASP.NET Core. This section covers the various improvements we’ve made to Razor Components in this preview update.

Single project template

The Razor Components project template is now a single project instead of two projects in the same solution. The authored Razor Components live directly in the ASP.NET Core app that hosts them. The same ASP.NET Core project can contain Razor Components, Pages, and Views. The Razor Components template also has HTTPS enabled by default like the other ASP.NET Core web app templates.

New .razor extension

Razor Components are authored using Razor syntax, but are compiled differently than Razor Pages and Views. To clarify which Razor files should be compiled as Razor Components we’ve introduced a new file extension: .razor. In the Razor Components template all component files now use the .razor extension. Razor Pages and Views still use the .cshtml extension.

Razor Components can still be authored using the .cshtml file extension as long as those files are identified as Razor Component files using the _RazorComponentInclude MSBuild property. For example, the Razor Component template in this release specifies that all .cshtml files under the Components folder should be treated as Razor Components.


Please note that there are a number of limitations with .razor files in this release. Please refer to the release notes for the list of known issues and available workarounds.

Endpoint routing integration

Razor Components are now integrated into ASP.NET Core’s new Endpoint Routing system. To enable Razor Components support in your application, use MapComponentHub<TComponent> within your routing configuration. For example,

app.UseRouting(routes =>
{ routes.MapRazorPages(); routes.MapComponentHub<App>("app");

This configures the application to accept incoming connections for interactive Razor Components, and specifies that the root component App should be rendered within a DOM element matching the selector app.


The Razor Components project template now does server-side prerendering by default. This means that when a user navigates to your application, the server will perform an initial render of your Razor Components and deliver the result to their browser as plain static HTML. Then, the browser will reconnect to the server via SignalR and switch the Razor Components into a fully interactive mode. This two-phase delivery is beneficial because:

  • It improves the perceived performance of the site, because the UI can appear sooner, without waiting to make any WebSocket connections or even running any client-side script. This makes a bigger difference for users on slow connections, such as 2G/3G mobiles.
  • It can make your application easily crawlable by search engines.

For users on faster connections, such as intranet users, this feature has less impact because the UI should appear near-instantly regardless.

To set up prerendering, the Razor Components project template no longer has a static HTML file. Instead a single Razor Page, /Pages/Index.cshtml, is used to prerender the app content using the Html.RenderComponentAsync<TComponent>() HTML helper. The page also references the components.server.js script to set up the SignalR connection after the content has been prerendered and downloaded. And because this is a Razor Page, features like the environment tag helper just work.


@page "{*clientPath}"
<!DOCTYPE html>
<head> ...
<body> <app>@(await Html.RenderComponentAsync<App>())</app> http://_framework/components.server.js

Besides the app loading faster, you can see that prerendering is happening by looking at the downloaded HTML source in the browser dev tools. The Razor Components are fully rendered in the HTML.

Razor Components in Razor Class Libraries

You can now add Razor Components to Razor Class Libraries and reference them from ASP.NET Core projects using Razor Components.

To create reusable Razor Components in a Razor Class Library:

  1. Create an Razor Components app:

    dotnet new razorcomponents -o RazorComponentsApp1
  2. Create a new Razor Class Library

    dotnet new razorclasslib -o RazorClassLib1
  3. Add a Component1.razor file to the Razor Class Library


<h1>Component1</h1> <p>@message</p> @functions { string message = "Hello from a Razor Class Library"!;
  1. Reference the Razor Class Library from an ASP.NET Core app using Razor Components:

    dotnet add RazorComponentsApp1 reference RazorClassLib1
  2. In the Razor Components app, import all components from the Razor Class Library using the @addTagHelper directive and then use Component1 in the app:


@page "/"
@addTagHelper *, RazorClassLib1 <h1>Hello, world!</h1> Welcome to your new app. <Component1 />

Note that Razor Class Libraries are not compatible with Blazor apps in this release. Also, Razor Class Libraries do not yet support static assets. To create components in a library that can be shared with Blazor and Razor Components apps you still need to use a Blazor Class Library. This is something we expect to address in a future update.

Improved event handling

The new EventCallback and EventCallback<> types make defining component callbacks much more straightforward. For example consider the following two components:


<button onclick="@OnClick">Click here and see what happens!</button> @functions { [Parameter] EventCallback<UIMouseEventArgs> OnClick { get; set; }


<MyButton OnClick="ShowMessage" /> @function { string text; void ShowMessage(UIMouseEventArgs e) { text = "Hello, world!"; } }

The OnClick callback is of type EventCallback<UIMouseEventArgs> (instead of Action<UIMouseEventArgs>), which MyButton passes off directly to the onclick event handler. The compiler handles converting the delegate to an EventCallback, and will do some other things to make sure that the rendering process has enough information to render the correct target component. As a result an explicit call to StateHasChanged in the ShowMessage event handler isn’t necessary.

By using the EventCallback<> type OnClick handler can now also be asynchronous without any additional code changes to MyButton:


<MyButton OnClick="ShowMessageAsync" /> @function { string text; async Task ShowMessageAsync(UIMouseEventArgs e) { await Task.Yield(); text = "Hello, world!"; } }

We recommend using EventCallback and EventCallback<T> when you define component parameters for event handling and binding. Use EventCallback<> where possible because it’s strongly typed and will provide better feedback to users of your component. Use EventCallback when there’s no value you will pass to the callback.

Note that consumers don’t have to write different code when using a component because of EventCallback. The same event handling code should still work, while removing some thorny issues and improving the usability of your components.

Forms & validation

This preview release adds built-in components and infrastructure for handling forms and validation.

One of the benefits of using .NET for client-side web development is the ability to share the same implementation logic between the client and the server. Validation logic is a prime example. The new forms & validation support in Razor Components includes support for handling validation using data annotations, or you can plug in your preferred validation system.

For example, the following Person type defines validation logic using data annotations:

public class Person
{ [Required(ErrorMessage = "Enter a name")] [StringLength(10, ErrorMessage = "That name is too long")] public string Name { get; set; } [Range(0, 200, ErrorMessage = "Nobody is that old")] public int AgeInYears { get; set; } [Required] [Range(typeof(bool), "true", "true", ErrorMessage = "Must accept terms")] public bool AcceptsTerms { get; set; }

Here’s how you can create a validating form based on this Person model:

<EditForm Model="@person" OnValidSubmit="@HandleValidSubmit"> <DataAnnotationsValidator /> <ValidationSummary /> <p class="name"> Name: <InputText bind-Value="@person.Name" /> </p> <p class="age"> Age (years): <InputNumber bind-Value="@person.AgeInYears" /> </p> <p class="accepts-terms"> Accepts terms: <InputCheckbox bind-Value="@person.AcceptsTerms" /> </p> <button type="submit">Submit</button>
</EditForm> @functions { Person person = new Person(); void HandleValidSubmit() { Console.WriteLine("OnValidSubmit"); }

If you add this form to your app and run it you will get a basic form that automatically validates the field inputs when they are changed and when the form is submitted.

Validating form

There are quite a few things going on here, so let’s break it down piece by piece:

  • The form is defined using the new EditForm component. The EditForm sets up an EditContext as a cascading value that tracks metadata about the edit process (e.g. what’s been modified, current validation messages, etc.). The EditForm also provides convenient events for valid and invalid submits (OnValidSubmit, OnInvalidSubmit). Or you can use OnSubmit directly if you want to trigger the validation yourself.
  • The DataAnnotationsValidator component attaches validation support using data annotations to the cascaded EditContext. Enabling support for validation using data annotations currently requires this explicit gesture, but we are considering making this the default behavior that you can then override.
  • Each of the form fields are defined using a set of built-in input components (InputText, InputNumber, InputCheckbox, InputSelect, etc.). These components provide default behavior for validating on edit and changing their CSS class to reflect the field state. Some of them have useful parsing logic (e.g., InputDate and InputNumber handle unparseable values gracefully by registering them as validation errors). The relevant ones also support nullability of the target field (e.g., int?).
  • The ValidationMessage component displays validation messages for a specific field.
  • The ValidationSummary component summarizes all validation messages (similar to the validation summary tag helper).

There are some limitations with the built-in input components that we expect to improve in future updates. For example, you can’t currently specify arbitrary attributes on the generate input tags. In the future, we plan to enable components that pass through all extra attributes. For now, you’ll need to build your own component subclasses to handle these cases.

Runtime compilation

Support for runtime compilation was removed from the ASP.NET Core shared framework in .NET Core 3.0, but you can now enable it by adding a package to your app.

To enable runtime compilation:

  1. Add a package reference to Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation

    <PackageReference Include="Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation" Version="3.0.0-preview3-19153-02" />
  2. In Startup.ConfigureServices add a call to AddRazorRuntimeCompilation


Worker Service Template

In 3.0.0-preview3 we are introducing a new template called ‘Worker Service’. This template is designed as a starting point for running long-running background processes like you might run as a Windows Service or Linux Daemon. Examples of this would be producing/consuming messages from a message queue or monitoring a file to process when it appears. It’s intended to provide the productivity features of ASP.NET Core such as Logging, DI, Configuration, etc without carrying any web dependencies.

Worker Service

In the coming days we will publish a few blog posts giving more walkthroughs on using the Worker template to get started. We will have dedicated posts about publishing as a Windows/Systemd service, running on ACI/AKS, as well as running as a WebJob.


Whilst the intent is for the worker template to not have any dependencies on web technologies by default, in preview3 it still uses the Web SDK and is shown after you select ‘ASP.NET Core WebApplication’ in Visual Studio. This is temporary and will be changed in a future preview. This means that for preview3 you will see many options in VS that may not make sense, such as publishing your worker as a web app to IIS.

Angular template updated to Angular 7

The Angular template is now updated to Angular 7. We anticipate updating again to Angular 8 before .NET Core 3.0 ships a stable release.

Authentication for the Single Page Application templates

This release introduces support for authentication in our Angular and React templates. In this section we show how to create a new Angular or React template that allows us to authenticate users and access a protected API resource.

Our support for authenticating and authorizing users is powered behind the scenes by IdentityServer, with some extensions we built to simplify the configuration experience for the scenarios we are targeting.

Note: In this post we showcase authentication support for Angular but the React template offers equivalent functionality.

Create a new Angular application

To create a new Angular application with authentication support we invoke the following command:

dotnet new angular -au Individual

This command creates a new ASP.NET Core application with a hosted client Angular application. The ASP.NET Core application includes an Identity Server instance already configured so that your Angular application can authenticate users and send HTTP requests against the protected resources in the ASP.NET Core application.

The authentication and authorization support is built as an Angular module that gets imported into your application and offers a suite of components and services to enhance the functionality of the main applicaiton module.

Run the application

To run the application simply execute the command below and open the browser in the url displayed on the console:

dotnet run
Hosting environment: Development
Content root path: C:\angularapp
Now listening on: https://localhost:5001
Now listening on: http://localhost:5000
Application started. Press Ctrl+C to shut down.

SPA index

When we open the application we see the usual Home, Counter and Fetch data menu options and two new options: Register and Login. If we click on Register we get sent to the default Identity UI where (after running migrations and updating the database) we can register as a new user.

Register a new user

SPA register

After registering as a new user we get redirected back to the application where we can see that we are successfully authenticated

SPA logged in

Call an authenticated API

If we click on the Fetch data we can see the weather forecast data table

SPA fetch data

Protect an existing API

To protect an API on the server we simply need to use the [Authorize] attribute on the controller or action that we want to protect.

public class SampleDataController : Controller

Require authentication for a client route.

To require the user be authenticated when visiting a page in the Angular application we apply the [AuthorizeGuard] to the route we are configuring.

import { ApiAuthorizationModule } from 'src/api-authorization/api-authorization.module';
import { AuthorizeGuard } from 'src/api-authorization/authorize.guard';
import { AuthorizeInterceptor } from 'src/api-authorization/authorize.interceptor'; @NgModule({ declarations: [ AppComponent, NavMenuComponent, HomeComponent, CounterComponent, FetchDataComponent ], imports: [ BrowserModule.withServerTransition({ appId: 'ng-cli-universal' }), HttpClientModule, FormsModule, ApiAuthorizationModule, RouterModule.forRoot([ { path: '', component: HomeComponent, pathMatch: 'full' }, { path: 'counter', component: CounterComponent }, { path: 'fetch-data', component: FetchDataComponent, canActivate: [AuthorizeGuard] }, ]) ], providers: [ { provide: HTTP_INTERCEPTORS, useClass: AuthorizeInterceptor, multi: true } ], bootstrap: [AppComponent]
export class AppModule { }

Get more details by visiting the docs page

This is a quick introduction to what our new authentication support for Single Page Applications has to offer. For more details check out the docs.

Endpoint Routing with SignalR Hubs

In 3.0.0-preview3 we are hooking SignalR hubs into the new Endpoint Routing feature recently released. SignalR hub wire-up was previously done explicitly:

app.UseSignalR(routes =>
{ routes.MapHub<ChatHub>("hubs/chat");

This meant developers would need to wire up controllers, Razor pages, and hubs in a variety of different places during startup, leading to a series of nearly-identical routing segments:

app.UseSignalR(routes =>
{ routes.MapHub<ChatHub>("hubs/chat");
}); app.UseRouting(routes =>
{ routes.MapRazorPages();

Now, SignalR hubs can also be routed via endpoint routing, so you’ve got a one-stop place to route nearly everything in ASP.NET Core.

app.UseRouting(routes =>
{ routes.MapRazorPages(); routes.MapHub<ChatHub>("hubs/chat");

Long Polling for Java SignalR Client

We added long polling support to the Java client which enables it to establish connections even in environments that do not support WebSockets. This also gives you the ability to specifically select the long polling transport in your client apps.

gRPC Template

This preview release introduces a new template for building gRPC services with ASP.NET Core using a new gRPC framework we are building in collaboration with Google.

gRPC is a popular RPC (remote procedure call) framework that offers an opinionated contract-first approach to API development. It uses HTTP/2 for transport, Protocol Buffers as the interface description language, and provides features such as authentication, bidirectional streaming and flow control, and cancellation and timeouts.

gRPC template

The templates create two projects: a gRPC service hosted inside ASP.NET Core, and a console application to test it with.

gRPC solution

This is the first public preview of gRPC for ASP.NET Core and it doesn’t implement all of gRPC’s features, but we’re working hard to make the best gRPC experience for ASP.NET possible. Please try it out and give us feedback at grpc/grpc-dotnet on GitHub.

Stay tuned for future blog posts discussing gRPC for ASP.NET Core in more detail.

Give feedback

We hope you enjoy the new features in this preview release of ASP.NET Core! Please let us know what you think by filing issues on Github.

Daniel Roth
Daniel Roth

Principal Program Manager, ASP.NET

Follow Daniel