golang-uber-fx

Inject fx.Lifecycle into your server constructor and append an fx.Hook. In OnStart, call net.Listen and launch srv.Serve in a goroutine so the hook returns quickly; in OnStop, call srv.Shutdown(ctx) for graceful shutdown.

fx is built on dig and shares the same DI primitives, but adds lifecycle hooks, fx.Module with scoped decorators, a signal-aware Run() loop, and structured event logging. Use fx for long-running services and raw dig for CLI tools or libraries that manage their own lifecycle.

Use fx.Annotate with fx.As, for example fx.Annotate(NewPostgresDB, fx.As(new(Database))). Add fx.ResultTags inside the same annotation for name or group tags, without writing a separate adapter constructor or fx.Out struct.

A blocking OnStart hook is the usual cause — long-running work must run in a goroutine so the hook returns quickly and dependent hooks can fire. Also verify every provided type is reachable from an fx.Invoke, since unreferenced constructors never run.

Use fxtest.New(t, ...) with fx.Replace to swap a real dependency for a fake, and fx.Populate(&target) to pull values out of the graph. Call app.RequireStart() and defer app.RequireStop() so failures call t.Fatal and teardown registers as cleanup.

Avoid fx for one-shot CLI tools or small object graphs where lifecycle and signal handling add no value — raw uber-go/dig or manual constructor injection is simpler. fx pays off when you need OnStart/OnStop ordering, modules, and graceful shutdown.