Adding .NET Aspire to existing ASP.NET Core Web API causes error on builder.MapDefaultEndpoints()

Question

I have added .NET Aspire to my ASP.NET Core Web API backend. But I get the following error when building the app on builder.MapDefaultEndpoints():

Error (active) CS1929 'WebApplicationBuilder' does not contain a definition for 'MapDefaultEndpoints' and the best extension method overload 'Extensions.MapDefaultEndpoints(WebApplication)' requires a receiver of type 'Microsoft.AspNetCore.Builder.WebApplication'

How can I solve this?

This is my program.cs:

try
{
    Log.Information("Starting Rest API");
    var builder = WebApplication.CreateBuilder(args);

    var startup = new Startup(builder.Configuration);

    startup.ConfigureServices(builder.Services);

    builder.AddServiceDefaults();
    builder.MapDefaultEndpoints();

    ConfigureLogger(builder.Host);

    var app = builder.Build();

    startup.Configure(app, app.Environment);

    app.Run();
}
catch (Exception ex)
{
    Log.Fatal(ex, "Host terminated unexpectedly");
}
finally
{
    Log.CloseAndFlush();
}

Yuning Duan · Accepted Answer · 2024-08-28 03:31:51Z

1

I reproduced your problem.

The reason is that WebApplicationBuilder does not have a MapDefaultEndpoints method. In the documentation, we can learn that MapDefaultEndpoints() is an extension method provided by .NET Aspire for configuring default endpoints. In the Extensions.cs file, we can see that:

public static WebApplication MapDefaultEndpoints(this WebApplication app)
{
     // Adding health checks endpoints to applications in non-development environments has security implications.
     // See https://aka.ms/dotnet/aspire/healthchecks for details before enabling these endpoints in non-development environments.
     if (app.Environment.IsDevelopment())
     {
         // All health checks must pass for app to be considered ready to accept traffic after starting
         app.MapHealthChecks("/health");

         // Only health checks tagged with the "live" tag must pass for app to be considered alive
         app.MapHealthChecks("/alive", new HealthCheckOptions
         {
             Predicate = r => r.Tags.Contains("live")
         });
     }

     return app;
}

The MapDefaultEndpoints method is defined as a WebApplication type, so This method should be called on WebApplication, not WebApplicationBuilder, we should move MapDefaultEndpoints() to the app object:

app.MapDefaultEndpoints();

edited Aug 28, 2024 at 3:31

answered Aug 27, 2024 at 6:43

Yuning Duan

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5 Comments

user3552264 Over a year ago

Tnx Yuning For your reply. i'll try it and let you know.

user3552264 Over a year ago

Hi Yuning. I Have added app.MapDefaultEndpoints() after var app = builder.Build() And it does compile now. But in the aspire dashboard i don't get the url under "endpoints". It says Endpoints None

user3552264 Over a year ago

I'm have also added swagger in my api

Yuning Duan Over a year ago

You can check if you have added the project to the application model in the App host project. For example:

var builder = DistributedApplication.CreateBuilder(args); builder.AddProject<Projects.WebApplication44>("webapplication44");

i.sstatic.net/buWe6ZUr.png Note: WebApplication44 is my sample API project, you should change it to your corresponding project.

Yuning Duan Over a year ago

For more .NET Aspire integration, you can refer to these documents:learn.microsoft.com/en-us/dotnet/aspire/fundamentals/… ,learn.microsoft.com/en-us/dotnet/aspire/get-started/… . If you still have questions, you can create a new case to ask.

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