Golang application framework using uber-go/fx — fx.New, fx.Provide, fx.Invoke, fx.Module, fx.Lifecycle hooks, fx.Annotate, fx.Decorate, fx.Supply, signal-aware Run(). Apply when using/adopting fx or the codebase imports go.uber.org/fx. Raw DI without lifecycle → golang-uber-dig.
Golang application framework using uber-go/fx — fx.New, fx.Provide, fx.Invoke, fx.Module, fx.Lifecycle hooks, fx.Annotate, fx.Decorate, fx.Supply, signal-aware Run(). Apply when using/adopting fx or the codebase imports go.uber.org/fx. Raw DI without lifecycle → golang-uber-dig.
user-invocable
true
license
MIT
compatibility
Designed for Claude Code, Codex or similar harness, and for projects using Golang.
Persona: You are a Go architect building a long-running service with fx. You wire the graph at the composition root, push lifecycle into hooks instead of init(), and treat modules as the unit of reuse.
Using uber-go/fx for Application Wiring in Go
Application framework combining a reflection-based DI container (built on uber-go/dig) with a lifecycle, module system, signal-aware run loop, and structured event logging. For long-running services where boot order, graceful shutdown, and modular composition matter.
This skill is not exhaustive. Please refer to library documentation and code examples for more information. For Go package docs, symbols, versions, importers, and known vulnerabilities, → See samber/cc-skills-golang@golang-pkg-go-dev skill (godig) — prefer it over Context7 for Go package facts. To navigate this library's usage in your own code (definitions, call sites, diagnostics), → See samber/cc-skills-golang@golang-gopls skill (gopls). Context7 remains a fallback for docs not indexed on pkg.go.dev.
go get go.uber.org/fx
fx vs. dig
fx is built on top of dig and shares the same reflection-based container engine. The DI primitives (Provide, Invoke, In/Out structs, named values, value groups) are identical — fx.In/fx.Out are re-exports of dig.In/dig.Out.
What fx adds on top:
Concern
dig
fx
DI container
✅ dig.New()
✅ (embedded)
Lifecycle hooks
❌
✅ fx.Lifecycle OnStart/OnStop
Module system
❌
✅ fx.Module with scoped decorators
Signal-aware run loop
❌
✅ app.Run() blocks on SIGINT/SIGTERM
Structured event logging
❌
✅ fx.WithLogger / fxevent
Startup/shutdown timeout
❌
✅ fx.StartTimeout / fx.StopTimeout
Choose fx for long-running services (HTTP servers, workers, daemons) — lifecycle and signal handling are mandatory there, and modules make large service graphs manageable.
Choose raw dig when you need wiring without a framework: CLI tools, libraries that expose a container to callers, test harnesses, or embedding DI into an existing app that manages its own lifecycle. See samber/cc-skills-golang@golang-uber-dig skill.
The Application
import"go.uber.org/fx"
app := fx.New(
fx.Provide(NewLogger, NewDatabase, NewServer),
fx.Invoke(RegisterRoutes),
)
app.Run() // blocks until SIGINT/SIGTERM, then runs OnStop hooks
Boot stages: fx.New validates types (constructors do not run); app.Start(ctx) runs each fx.Invoke and fires OnStart hooks in topological order; main blocks on app.Done(); app.Stop(ctx) fires OnStop hooks in reverse order. Default timeout is 15 seconds — override with fx.StartTimeout / fx.StopTimeout.
Provide and Invoke
fx.New(
fx.Provide(NewLogger, NewDatabase, NewServer), // lazy
fx.Invoke(RegisterRoutes, StartMetricsExporter), // always run during Start
)
fx.Provide registers constructors; fx.Invoke is the trigger — without an Invoke (directly or transitively) referencing a type, its constructor never runs.
Lifecycle Hooks
Inject fx.Lifecycle and append hooks. Constructors should return quickly; long-running work belongs in OnStart.
funcNewHTTPServer(lc fx.Lifecycle, log *zap.Logger, cfg *Config) *http.Server {
srv := &http.Server{Addr: cfg.Addr}
lc.Append(fx.Hook{
OnStart: func(ctx context.Context)error {
ln, err := net.Listen("tcp", srv.Addr)
if err != nil { return err }
go srv.Serve(ln) // blocking work in a goroutinereturnnil
},
OnStop: func(ctx context.Context)error {
return srv.Shutdown(ctx)
},
})
return srv
}
Both callbacks receive a context bounded by StartTimeout/StopTimeout — respect cancellation. OnStart must return quickly — spawn a goroutine for blocking work; otherwise startup hangs and dependent hooks never fire.
fx.StartHook / fx.StopHook / fx.StartStopHook adapt simpler signatures (no context, no error, or both):
Many constructors, one consumer slice — typical for routes, health checks, metrics collectors:
type RouteResult struct {
fx.Out
Handler http.Handler `group:"routes"`
}
type ServerParams struct {
fx.In
Routes []http.Handler `group:"routes"`
}
Append ,flatten (group:"routes,flatten") to unwrap a slice instead of nesting it. Order is not guaranteed — provide an explicit ordered slice when sequence matters.
fx.Module
fx.Module groups providers, invokes, and decorators under a name. Modules scope decorators to themselves and their children — a logger renamed in fx.Module("db", ...) only appears renamed for code inside that module.
Treat each module as a small library that can be lifted into another app — its public surface is the types it Provides.
For fx.Supply/fx.Replace/fx.Decorate, optional deps, custom logging, manual lifecycle, and Quick Reference, see advanced.md.
Best Practices
Keep main() thin — providers, modules, and a single Run(). Push real work into modules so each can be tested in isolation.
Use lifecycle hooks instead of init() or goroutines launched from constructors — Start/Stop ordering depends on graph topology, but init() goroutines do not, which leads to races and leaks.
OnStart must return promptly — long work goes in a goroutine inside the hook. A blocking OnStart hangs the rest of the boot.
Respect ctx.Done() in hooks — a hook that ignores cancellation is reported as a timeout failure but its goroutine continues, leaking resources.
Group by module, not by layer — a module owns the providers, lifecycle, and decorators for one concern (HTTP, DB, metrics).
Use fx.Annotate for tags rather than wrapping a constructor in an fx.Out struct — keeps the constructor reusable outside fx.
Replace fx.Provide with fx.Supply for pre-built values (config, command-line flags). Shorter, signals intent.
Validate the graph in CI by booting under fx.New(...).Err() — catches missing providers and cycles before deploy.
Common Mistakes
Mistake
Fix
Long-running work directly in OnStart
Spawn a goroutine inside OnStart; the hook itself must return quickly so dependent hooks can run.
fx.Provide something that should be fx.Supply
Pre-built values (config, secrets) belong in fx.Supply — clearer and avoids a no-op constructor.
Module decorator leaking to siblings
Decorate inside fx.Module(...) — decorators flow only to descendants. A top-level fx.Decorate is global.
Group order assumed
Groups are unordered. If order matters, provide an ordered slice from one constructor.
Constructors with side effects
Side effects belong in OnStart — constructors should be cheap and pure-ish, since they may run concurrently and lazily.
Forgotten fx.Invoke
Without an Invoke (or downstream consumer), constructors never run. Add at least one Invoke per app.
Testing
Use go.uber.org/fx/fxtest to integrate fx with *testing.T (failures call t.Fatal, RequireStop registers as t.Cleanup). fx.Populate(&target) pulls values out of the graph; fx.Replace swaps real dependencies for fakes. Full patterns in testing.md.
recipes.md — full HTTP service with database/metrics, background workers with graceful drain, multiple impls of the same interface, manual lifecycle for CLI embedding
