.NET Aspire service defaults

In this article, you learn about the .NET Aspire service defaults project, a set of extension methods that:

• Connect telemetry, health checks, service discovery to your app.
• Are customizable and extensible.

Cloud-native applications often require extensive configurations to ensure they work across different environments reliably and securely. .NET Aspire provides many helper methods and tools to streamline the management of configurations for OpenTelemetry, health checks, environment variables, and more.

Explore the service defaults project

When you either Enlist in .NET Aspire orchestration or create a new .NET Aspire project, the YourAppName.ServiceDefaults.csproj project is added to your solution. For example, when building an API, you call the AddServiceDefaults method in the Program.cs file of your apps:

builder.AddServiceDefaults();

The AddServiceDefaults method handles the following tasks:

• Configures OpenTelemetry metrics and tracing.
• Adds default health check endpoints.
• Adds service discovery functionality.
• Configures HttpClient to work with service discovery.

For more information, see Provided extension methods for details on the AddServiceDefaults method.

Important

The .NET Aspire service defaults project is specifically designed for sharing the Extensions.cs file and its functionality. Don't include other shared functionality or models in this project. Use a conventional shared class library project for those purposes.

Project characteristics

The YourAppName.ServiceDefaults project is a .NET 9.0 library that contains the following XML:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>net9.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
    <IsAspireSharedProject>true</IsAspireSharedProject>
  </PropertyGroup>

  <ItemGroup>
    <FrameworkReference Include="Microsoft.AspNetCore.App" />

    <PackageReference Include="Microsoft.Extensions.Http.Resilience" Version="9.0.0" />
    <PackageReference Include="Microsoft.Extensions.ServiceDiscovery" Version="9.0.0" />
    <PackageReference Include="OpenTelemetry.Exporter.OpenTelemetryProtocol" Version="1.10.0" />
    <PackageReference Include="OpenTelemetry.Extensions.Hosting" Version="1.10.0" />
    <PackageReference Include="OpenTelemetry.Instrumentation.AspNetCore" Version="1.10.1" />
    <PackageReference Include="OpenTelemetry.Instrumentation.Http" Version="1.10.0" />
    <PackageReference Include="OpenTelemetry.Instrumentation.Runtime" Version="1.10.0" />
  </ItemGroup>

</Project>

The service defaults project template imposes a FrameworkReference dependency on Microsoft.AspNetCore.App.

Tip

If you don't want to take a dependency on Microsoft.AspNetCore.App, you can create a custom service defaults project. For more information, see Custom service defaults.

The IsAspireSharedProject property is set to true, which indicates that this project is a shared project. The .NET Aspire tooling uses this project as a reference for other projects added to a .NET Aspire solution. When you enlist the new project for orchestration, it automatically references the YourAppName.ServiceDefaults project and updates the Program.cs file to call the AddServiceDefaults method.

Provided extension methods

The YourAppName.ServiceDefaults project exposes a single Extensions.cs file that contains several opinionated extension methods:

• AddServiceDefaults: Adds service defaults functionality.
• ConfigureOpenTelemetry: Configures OpenTelemetry metrics and tracing.
• AddDefaultHealthChecks: Adds default health check endpoints.
• MapDefaultEndpoints: Maps the health checks endpoint to /health and the liveness endpoint to /alive.

Add service defaults functionality

The AddServiceDefaults method defines default configurations with the following opinionated functionality:

public static IHostApplicationBuilder AddServiceDefaults(
    this IHostApplicationBuilder builder)
{
    builder.ConfigureOpenTelemetry();

    builder.AddDefaultHealthChecks();

    builder.Services.AddServiceDiscovery();

    builder.Services.ConfigureHttpClientDefaults(http =>
    {
        // Turn on resilience by default
        http.AddStandardResilienceHandler();

        // Turn on service discovery by default
        http.AddServiceDiscovery();
    });

    // Uncomment the following to restrict the allowed schemes for service discovery.
    // builder.Services.Configure<ServiceDiscoveryOptions>(options =>
    // {
    //     options.AllowedSchemes = ["https"];
    // });

    return builder;
}

The preceding code:

• Configures OpenTelemetry metrics and tracing, by calling the ConfigureOpenTelemetry method.
• Adds default health check endpoints, by calling the AddDefaultHealthChecks method.
• Adds service discovery functionality, by calling the AddServiceDiscovery method.
• Configures HttpClient defaults, by calling the ConfigureHttpClientDefaults method—which is based on Build resilient HTTP apps: Key development patterns:
  • Adds the standard HTTP resilience handler, by calling the AddStandardResilienceHandler method.
  • Specifies that the IHttpClientBuilder should use service discovery, by calling the UseServiceDiscovery method.
• Returns the IHostApplicationBuilder instance to allow for method chaining.

OpenTelemetry configuration

Telemetry is a critical part of any cloud-native application. .NET Aspire provides a set of opinionated defaults for OpenTelemetry, which are configured with the ConfigureOpenTelemetry method:

public static IHostApplicationBuilder ConfigureOpenTelemetry(
    this IHostApplicationBuilder builder)
{
    builder.Logging.AddOpenTelemetry(logging =>
    {
        logging.IncludeFormattedMessage = true;
        logging.IncludeScopes = true;
    });

    builder.Services.AddOpenTelemetry()
        .WithMetrics(metrics =>
        {
            metrics.AddAspNetCoreInstrumentation()
                .AddHttpClientInstrumentation()
                .AddRuntimeInstrumentation();
        })
        .WithTracing(tracing =>
        {
            if (builder.Environment.IsDevelopment())
            {
                // We want to view all traces in development
                tracing.SetSampler(new AlwaysOnSampler());
            }

            tracing.AddAspNetCoreInstrumentation()
                // Uncomment the following line to enable gRPC instrumentation 
                // (requires the OpenTelemetry.Instrumentation.GrpcNetClient package)
                //.AddGrpcClientInstrumentation()
                .AddHttpClientInstrumentation();
        });

    builder.AddOpenTelemetryExporters();

    return builder;
}

The ConfigureOpenTelemetry method:

• Adds .NET Aspire telemetry logging to include formatted messages and scopes.
• Adds OpenTelemetry metrics and tracing that include:
  • Runtime instrumentation metrics.
  • ASP.NET Core instrumentation metrics.
  • HttpClient instrumentation metrics.
  • In a development environment, the AlwaysOnSampler is used to view all traces.
  • Tracing details for ASP.NET Core, gRPC and HTTP instrumentation.
• Adds OpenTelemetry exporters, by calling AddOpenTelemetryExporters.

The AddOpenTelemetryExporters method is defined privately as follows:

private static IHostApplicationBuilder AddOpenTelemetryExporters(
    this IHostApplicationBuilder builder)
{
    var useOtlpExporter = !string.IsNullOrWhiteSpace(
        builder.Configuration["OTEL_EXPORTER_OTLP_ENDPOINT"]);

    if (useOtlpExporter)
    {
        builder.Services.Configure<OpenTelemetryLoggerOptions>(
            logging => logging.AddOtlpExporter());
        builder.Services.ConfigureOpenTelemetryMeterProvider(
            metrics => metrics.AddOtlpExporter());
        builder.Services.ConfigureOpenTelemetryTracerProvider(
            tracing => tracing.AddOtlpExporter());
    }

    // Uncomment the following lines to enable the Prometheus exporter
    // (requires the OpenTelemetry.Exporter.Prometheus.AspNetCore package)
    // builder.Services.AddOpenTelemetry()
    //    .WithMetrics(metrics => metrics.AddPrometheusExporter());

    // Uncomment the following lines to enable the Azure Monitor exporter 
    // (requires the Azure.Monitor.OpenTelemetry.AspNetCore package)
    //if (!string.IsNullOrEmpty(
    //    builder.Configuration["APPLICATIONINSIGHTS_CONNECTION_STRING"]))
    //{
    //    builder.Services.AddOpenTelemetry()
    //       .UseAzureMonitor();
    //}

    return builder;
}

The AddOpenTelemetryExporters method adds OpenTelemetry exporters based on the following conditions:

• If the OTEL_EXPORTER_OTLP_ENDPOINT environment variable is set, the OpenTelemetry exporter is added.
• Optionally consumers of .NET Aspire service defaults can uncomment some code to enable the Prometheus exporter, or the Azure Monitor exporter.

For more information, see .NET Aspire telemetry.

Health checks configuration

Health checks are used by various tools and systems to assess the readiness of your app. .NET Aspire provides a set of opinionated defaults for health checks, which are configured with the AddDefaultHealthChecks method:

public static IHostApplicationBuilder AddDefaultHealthChecks(
    this IHostApplicationBuilder builder)
{
    builder.Services.AddHealthChecks()
        // Add a default liveness check to ensure app is responsive
        .AddCheck("self", () => HealthCheckResult.Healthy(), ["live"]);

    return builder;
}

The AddDefaultHealthChecks method adds a default liveness check to ensure the app is responsive. The call to AddHealthChecks registers the HealthCheckService. For more information, see .NET Aspire health checks.

Web app health checks configuration

To expose health checks in a web app, .NET Aspire automatically determines the type of project being referenced within the solution, and adds the appropriate call to MapDefaultEndpoints:

public static WebApplication MapDefaultEndpoints(this WebApplication app)
{
    // Uncomment the following line to enable the Prometheus endpoint 
    // (requires the OpenTelemetry.Exporter.Prometheus.AspNetCore package)
    // app.MapPrometheusScrapingEndpoint();

    // 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:

• Allows consumers to optionally uncomment some code to enable the Prometheus endpoint.
• Maps the health checks endpoint to /health.
• Maps the liveness endpoint to /alive route where the health check tag contains live.

For more information, see .NET Aspire health checks.

Custom service defaults

If the default service configuration provided by the project template is not sufficient for your needs, you have the option to create your own service defaults project. This is especially useful when your consuming project, such as a Worker project or WinForms project, cannot or does not want to have a FrameworkReference dependency on Microsoft.AspNetCore.App.

To do this, create a new .NET 9.0 class library project and add the necessary dependencies to the project file, consider the following example:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Library</OutputType>
    <TargetFramework>net9.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.Extensions.Hosting" />
    <PackageReference Include="Microsoft.Extensions.ServiceDiscovery" />
    <PackageReference Include="Microsoft.Extensions.Http.Resilience" />
    <PackageReference Include="OpenTelemetry.Exporter.OpenTelemetryProtocol" />
    <PackageReference Include="OpenTelemetry.Extensions.Hosting" />
    <PackageReference Include="OpenTelemetry.Instrumentation.Http" />
    <PackageReference Include="OpenTelemetry.Instrumentation.Runtime" />
  </ItemGroup>
</Project>

Then create an extensions class that contains the necessary methods to configure the app defaults:

using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using OpenTelemetry.Logs;
using OpenTelemetry.Metrics;
using OpenTelemetry.Trace;

namespace Microsoft.Extensions.Hosting;

public static class AppDefaultsExtensions
{
    public static IHostApplicationBuilder AddAppDefaults(
        this IHostApplicationBuilder builder)
    {
        builder.ConfigureAppOpenTelemetry();

        builder.Services.AddServiceDiscovery();

        builder.Services.ConfigureHttpClientDefaults(http =>
        {
            // Turn on resilience by default
            http.AddStandardResilienceHandler();

            // Turn on service discovery by default
            http.AddServiceDiscovery();
        });

        return builder;
    }

    public static IHostApplicationBuilder ConfigureAppOpenTelemetry(
        this IHostApplicationBuilder builder)
    {
        builder.Logging.AddOpenTelemetry(logging =>
        {
            logging.IncludeFormattedMessage = true;
            logging.IncludeScopes = true;
        });

        builder.Services.AddOpenTelemetry()
            .WithMetrics(static metrics =>
            {
                metrics.AddRuntimeInstrumentation();
            })
            .WithTracing(tracing =>
            {
                if (builder.Environment.IsDevelopment())
                {
                    // We want to view all traces in development
                    tracing.SetSampler(new AlwaysOnSampler());
                }

                tracing.AddGrpcClientInstrumentation()
                       .AddHttpClientInstrumentation();
            });

        builder.AddOpenTelemetryExporters();

        return builder;
    }

    private static IHostApplicationBuilder AddOpenTelemetryExporters(
        this IHostApplicationBuilder builder)
    {
        var useOtlpExporter =
            !string.IsNullOrWhiteSpace(
                builder.Configuration["OTEL_EXPORTER_OTLP_ENDPOINT"]);

        if (useOtlpExporter)
        {
            builder.Services.Configure<OpenTelemetryLoggerOptions>(
                logging => logging.AddOtlpExporter());
            builder.Services.ConfigureOpenTelemetryMeterProvider(
                metrics => metrics.AddOtlpExporter());
            builder.Services.ConfigureOpenTelemetryTracerProvider(
                tracing => tracing.AddOtlpExporter());
        }

        return builder;
    }
}

This is only an example, and you can customize the AppDefaultsExtensions class to meet your specific needs.

Next steps

This code is derived from the .NET Aspire Starter Application template and is intended as a starting point. You're free to modify this code however you deem necessary to meet your needs. It's important to know that service defaults project and its functionality are automatically applied to all project resources in a .NET Aspire solution.

• Service discovery in .NET Aspire
• .NET Aspire SDK
• .NET Aspire templates
• Health checks in .NET Aspire
• .NET Aspire telemetry
• Build resilient HTTP apps: Key development patterns