How do you implement graceful shutdown of an HTTP server in Go?

Graceful shutdown means: stop accepting new connections, wait for in-flight requests to complete, then exit. This prevents data loss and connection resets for clients whose requests are mid-flight when a deployment or restart occurs.

func main() {
    srv := &http.Server{
        Addr:    ":8080",
        Handler: buildRouter(),
    }

    // Start server in background
    serverErr := make(chan error, 1)
    go func() {
        log.Println("listening on :8080")
        if err := srv.ListenAndServe(); err != nil {
            serverErr <- err
        }
    }()

    // Wait for shutdown signal or server error
    shutdown := make(chan os.Signal, 1)
    signal.Notify(shutdown, syscall.SIGINT, syscall.SIGTERM)

    select {
    case err := <-serverErr:
        if !errors.Is(err, http.ErrServerClosed) {
            log.Fatalf("server error: %v", err)
        }
    case sig := <-shutdown:
        log.Printf("received signal: %v — shutting down", sig)
    }

    // Give in-flight requests up to 30s to complete
    ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
    defer cancel()

    if err := srv.Shutdown(ctx); err != nil {
        // Deadline exceeded: force close remaining connections
        log.Printf("forced shutdown: %v", err)
        srv.Close()
    }

    // Clean up other resources
    db.Close()
    log.Println("shutdown complete")
}

// In Kubernetes: SIGTERM is sent ~30s before SIGKILL
// The 30s graceful period must be < terminationGracePeriodSeconds
// Also set preStop lifecycle hook to delay pod removal from endpoints

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