.NET Aspire

Trigger On

• Aspire.AppHost.Sdk, Aspire.Hosting.*, DistributedApplication.CreateBuilder, WithReference, WaitFor, AddProject, AddRedis, AddPostgres, aspire run, aspire init, aspire add, or aspire update
• Aspire.Hosting.Testing, DistributedApplicationTestingBuilder, or a test harness that mixes an Aspire AppHost with WebApplicationFactory
• orchestrating multiple services and resources with an AppHost for local development or cloud deployment
• setting up ServiceDefaults, service discovery, OpenTelemetry, health checks, or the Aspire Dashboard
• choosing between official first-party Aspire integrations and CommunityToolkit/Aspire
• upgrading older 8.x or 9.x Aspire solutions to the current CLI and AppHost SDK model
• wiring polyglot services into an Aspire topology, especially when Go, Java, Python, or extra dev-time tools enter the picture

Workflow

1. Classify the task first: new AppHost creation, existing-solution enlistment, integration wiring, testing and observability, deployment, or version upgrade.
2. Prefer the current Aspire toolchain. For greenfield or modernized work, use the Aspire CLI and current AppHost SDK instead of writing new guidance around the deprecated legacy workload.
3. Treat 13.1.x patches as servicing updates, not a new app model. Keep the Aspire CLI, Aspire.AppHost.Sdk, and closely coupled hosting or testing packages on the same patch line, then rerun the AppHost and deployment checks after aspire update.
4. Keep the AppHost code-first and topology-focused. Model services, resources, dependencies, endpoints, lifetimes, and parameters there; keep business logic out.
5. Keep ServiceDefaults narrow. It exists for telemetry, health checks, resilience, and service discovery, not shared domain models or general utility code.
6. Prefer official first-party Aspire integrations when they cover the requirement. Use CommunityToolkit/Aspire only when the capability gap is real: unsupported language hosts, extra dev infrastructure, or extension packages the official project does not provide.
7. Validate the whole distributed system, not one project in isolation. Local success means the AppHost starts cleanly, dependencies resolve through WithReference, the dashboard shows the expected resource graph, and end-to-end tests can exercise the topology.
8. For integration tests, keep one shared AppHost fixture per test session. Use Aspire.Hosting.Testing to boot the distributed app, create HttpClient or SignalR clients from the AppHost, and layer WebApplicationFactory on top only when tests need direct Host DI, grains, or runtime services.
9. When publishing, switch from local containers or emulators to managed resources deliberately and verify which services truly need external endpoints.

Architecture

flowchart LR
  A["Distributed-app task"] --> B{"Need code-first orchestration?"}
  B -->|No| C["Stay in service-level skills such as ASP.NET Core, Worker, or Orleans"]
  B -->|Yes| D["Create or update the AppHost"]
  D --> E["Model resources and services with `WithReference` and `WaitFor`"]
  E --> F{"Official Aspire integration exists?"}
  F -->|Yes| G["Use first-party Aspire integration"]
  F -->|No or gap remains| H["Evaluate `CommunityToolkit/Aspire`"]
  G --> I["Apply `ServiceDefaults`, dashboard, and tests"]
  H --> I
  I --> J{"Publishing now?"}
  J -->|No| K["Run locally with `aspire run` or the AppHost project"]
  J -->|Yes| L["Choose `azd`, App Service, or the CLI deploy/publish pipeline"]

Current Guidance

• AppHost shape: prefer current SDK-style AppHost projects using Aspire.AppHost.Sdk/<version> or a file-based AppHost when that repo intentionally uses the single-file model. Recognize both as valid current patterns.
• CLI entry points: use aspire new for starter projects, aspire init to add Aspire support to an existing solution or create a single-file AppHost, aspire add to add integrations or starter pieces, aspire run for local orchestration, aspire deploy for the current CLI deploy pipeline, and aspire update for version-aware upgrades. aspire publish still exists for explicit artifact-generation flows and remains preview-sensitive.
• Patch posture: Aspire 13.1.3 is a servicing release. Treat it as a patch-line refresh for the current CLI-first workflow, not a new topology model; align package versions, rerun aspire update, then revalidate local orchestration and the chosen deployment path.
• App model wiring: use WithReference(...) for dependency and configuration flow, and WaitFor(...) for startup ordering. Use WithExternalHttpEndpoints() only when the resource truly needs an externally reachable endpoint for the chosen runtime or publish target.
• ServiceDefaults boundaries: AddServiceDefaults() should stay focused on OpenTelemetry, health endpoints, service discovery, HttpClient resilience, and related cross-cutting infrastructure.
• Testing model: prefer Aspire closed-box testing when you need to run the distributed application as a system. Use DistributedApplicationTestingBuilder plus a shared fixture for AppHost lifecycle, App.CreateHttpClient(...) for resource-bound clients, and a WebApplicationFactory<TEntryPoint> wrapper only when the test must resolve DI services or in-process runtime state from the hosted app. For UI flows, initialize Playwright once in the shared fixture, create a fresh browser context per test, and capture failure artifacts.
• Dashboard usage: treat the Aspire Dashboard as the development observability surface. It is valuable in AppHost runs and standalone OTLP scenarios, but it is not a production monitoring replacement.
• Upgrade posture: older 8.x or 9.x solutions need explicit migration work. Current guidance favors the Aspire CLI upgrade path and the newer AppHost SDK structure on .NET 10.

Selection Rules

• Use first-party Aspire when the package and docs exist for the resource or platform, especially for core .NET, Azure, cache, database, messaging, and standard local-container flows.
• Use CommunityToolkit/Aspire when you need polyglot app hosts beyond official coverage, extra dev-time tools around a resource, or community-maintained integrations such as SQLite, Java, Go, PowerShell, k6, MailPit, MinIO, or Meilisearch.
• Prefer the smallest surface that solves the problem. Do not add a broad toolkit extension pack when an existing first-party integration plus a normal library already fits.
• Treat toolkit packages as community-supported. Verify maturity, maintenance, external container images, and security or licensing assumptions before making them part of a production baseline.

Official Sources

• Aspire docs home
• AppHost
• Service defaults
• Integrations overview
• Build your first app
• Aspire CLI reference
• Upgrade Aspire
• Testing overview
• dotnet/aspire
• CommunityToolkit/Aspire

Anti-Patterns

• hardcoding service URLs or connection strings instead of using WithReference
• putting business logic, data migrations, or large configuration transforms inside the AppHost
• turning ServiceDefaults into a dumping ground for shared models or helpers
• adding external HTTP endpoints everywhere instead of only where runtime or publish needs them
• defaulting to CommunityToolkit/Aspire when first-party Aspire already covers the requirement
• assuming the dashboard or local containers automatically mean production readiness
• treating Aspire tests as a mocking framework; they run the application as a real distributed system

Deliver

• a version-aware Aspire architecture or upgrade direction
• the right AppHost, ServiceDefaults, integration, and CLI workflow
• an explicit first-party versus CommunityToolkit/Aspire package decision
• an end-to-end validation path for local orchestration, testing, and deployment

Validate

• the AppHost starts cleanly via aspire run or the AppHost project
• resources and projects are modeled with explicit WithReference and WaitFor relationships where needed
• consuming apps resolve endpoints and connection strings without hardcoded values
• ServiceDefaults contains only cross-cutting infrastructure concerns
• dashboard, health checks, logs, and traces reflect the expected resource graph
• Aspire-backed integration tests reuse a shared AppHost fixture instead of booting the distributed app inside each test
• any WebApplicationFactory layer reuses connection strings and endpoints from the AppHost instead of duplicating local config
• testing and deployment guidance matches the chosen runtime: local AppHost, standalone dashboard, ACA/App Service, or the CLI deploy/publish pipeline

References

• patterns.md - Current CLI-first setup flows, AppHost patterns, ServiceDefaults, testing, and upgrade checkpoints
• testing.md - Shared AppHost fixtures, DistributedApplicationTestingBuilder, WebApplicationFactory integration, Playwright bootstrapping, and diagnostics
• deployment.md - ACA, App Service, publish-mode, and manifest-oriented deployment guidance
• community-toolkit.md - Practical guide to CommunityToolkit/Aspire packages, capability gaps, and selection rules