How do you manage environment-specific settings and feature flags in Go?

Production Go applications distinguish between environments (development, staging, production) through configuration — not through build tags or conditional compilation. Feature flags allow gradual rollouts without redeployment.

// Environment detection via config
type Environment string

const (
    EnvDevelopment Environment = "development"
    EnvStaging     Environment = "staging"
    EnvProduction  Environment = "production"
)

type Config struct {
    Env          Environment
    Debug        bool
    LogLevel     slog.Level
    // ...
}

func loadConfig() *Config {
    env := Environment(os.Getenv("APP_ENV"))
    if env == "" { env = EnvDevelopment }

    cfg := &Config{Env: env}
    switch env {
    case EnvProduction:
        cfg.LogLevel = slog.LevelInfo
        cfg.Debug = false
    default:
        cfg.LogLevel = slog.LevelDebug
        cfg.Debug = true
    }
    return cfg
}

// Simple feature flag implementation
type FeatureFlags struct {
    mu    sync.RWMutex
    flags map[string]bool
}

func (f *FeatureFlags) IsEnabled(name string) bool {
    f.mu.RLock()
    defer f.mu.RUnlock()
    return f.flags[name]
}

func (f *FeatureFlags) Set(name string, enabled bool) {
    f.mu.Lock()
    defer f.mu.Unlock()
    f.flags[name] = enabled
}

// In a handler:
func userHandler(w http.ResponseWriter, r *http.Request) {
    if flags.IsEnabled("new-user-dashboard") {
        renderNewDashboard(w, r)
        return
    }
    renderLegacyDashboard(w, r)
}

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