Aspire Configuration

When to Use This Skill

Use this skill when:

• Wiring AppHost resources to application configuration in Aspire-based repos
• Ensuring production configuration is transparent and portable outside of Aspire
• Avoiding Aspire client/service-discovery packages inside application code
• Designing feature toggles for dev/test without changing app code paths

Core Principles

1. AppHost owns Aspire infrastructure packages
   • Aspire Hosting packages belong in AppHost only.
   • App projects should not reference Aspire client/service-discovery packages.
2. Explicit configuration only
   • AppHost must translate resource outputs into explicit config keys (env vars).
   • App code binds to IOptions<T> or Configuration only.
3. Production parity and transparency
   • Every value injected by AppHost must be representable in production as env vars or config files without Aspire.
   • Avoid opaque service discovery and implicit configuration.

Configuration Flow

AppHost resource -> WithEnvironment(...) -> app config keys -> IOptions<T> in app

The AppHost is responsible for turning Aspire resources into explicit app settings. The application never consumes Aspire clients or service discovery directly.

AppHost Patterns (Explicit Mapping)

Example: Database + Blob Storage

// AppHost/Program.cs
var builder = DistributedApplication.CreateBuilder(args);

var postgres = builder.AddPostgres("postgres");
var db = postgres.AddDatabase("appdb");

var minio = builder.AddContainer("minio", "minio/minio")
    .WithArgs("server", "/data")
    .WithHttpEndpoint(targetPort: 9000, name: "http")
    .WithHttpEndpoint(targetPort: 9001, name: "console")
    .WithEnvironment("MINIO_ROOT_USER", "minioadmin")
    .WithEnvironment("MINIO_ROOT_PASSWORD", "minioadmin");

var api = builder.AddProject<Projects.MyApp_Api>("api")
    .WithReference(db, "Postgres")
    .WithEnvironment("BlobStorage__Enabled", "true")
    .WithEnvironment("BlobStorage__ServiceUrl", minio.GetEndpoint("http"))
    .WithEnvironment("BlobStorage__AccessKey", "minioadmin")
    .WithEnvironment("BlobStorage__SecretKey", "minioadmin")
    .WithEnvironment("BlobStorage__Bucket", "attachments")
    .WithEnvironment("BlobStorage__ForcePathStyle", "true");

builder.Build().Run();

Key points

• WithReference(db, "Postgres") sets ConnectionStrings__Postgres explicitly.
• Every external dependency is represented via explicit config keys.
• The API project only reads Configuration values.

App Code Pattern (No Aspire Clients)

Application code binds to options and initializes SDKs directly. It never depends on Aspire client packages or service discovery.

// Api/Program.cs
builder.Services
    .AddOptions<BlobStorageOptions>()
    .BindConfiguration("BlobStorage")
    .ValidateDataAnnotations()
    .ValidateOnStart();

builder.Services.AddSingleton<IBlobStorageService>(sp =>
{
    var options = sp.GetRequiredService<IOptions<BlobStorageOptions>>().Value;
    return new S3BlobStorageService(options); // uses explicit options only
});

Do not add Aspire client packages (or AddServiceDiscovery) to the app. Those are orchestration concerns and should stay in AppHost.

Feature Toggles and Test Overrides

Keep toggles in config and drive them through AppHost and test fixtures. This maintains parity between dev/test and production configuration.

// AppHost: disable persistence in tests via config overrides
var config = builder.Configuration.GetSection("App")
    .Get<AppHostConfiguration>() ?? new AppHostConfiguration();

if (!config.UseVolumes)
{
    postgres.WithDataVolume(false);
}

api.WithEnvironment("BlobStorage__Enabled", config.EnableBlobStorage.ToString());

See skills/aspire/integration-testing/SKILL.md for patterns on passing configuration overrides into DistributedApplicationTestingBuilder.

Do / Don’t Checklist

Do

• Map every Aspire resource output to explicit configuration keys
• Use IOptions<T> with validation for all infrastructure settings
• Keep AppHost as the only place that references Aspire hosting packages
• Ensure any AppHost-injected value can be set in production env vars

Don’t

• Reference Aspire client/service-discovery packages in application projects
• Rely on opaque service discovery that cannot be mirrored in production
• Hide configuration behind Aspire-only abstractions

Related Skills

• skills/aspire/service-defaults/SKILL.md
• skills/aspire/integration-testing/SKILL.md
• skills/akka/aspire-configuration/SKILL.md

Resources

• Aspire AppHost environment configuration: https://learn.microsoft.com/en-us/dotnet/aspire/fundamentals/app-host
• Configuration in .NET: https://learn.microsoft.com/en-us/dotnet/core/extensions/configuration