feat: add resilient container restart controls

cmd/dyndns-web/main.go

@@ -9,6 +9,7 @@ import (
 	"os/signal"
 	"path/filepath"
 	"strings"
+	"sync"
 	"syscall"
 	"time"
 
@@ -66,6 +67,7 @@ func commandForInvocation(arguments []string) string {
 }
 
 func run(logger *slog.Logger) error {
+	startedAt := time.Now()
 	// Credentials and session data must never inherit a permissive process umask.
 	syscall.Umask(0o077)
 	cfg, err := config.Load()
@@ -103,7 +105,22 @@ func run(logger *slog.Logger) error {
 			logger.Info("removed AAAA records for disabled IPv6", "count", deleted)
 		}
 	}
-	serverUI, err := web.New(cfg, database, cipher, updater, softwareUpdates, logger)
+	restartRequested := make(chan struct{})
+	var restartOnce sync.Once
+	requestRestart := func() {
+		restartOnce.Do(func() {
+			// Docker applies restart policies only after a container has stayed up
+			// long enough to be considered successfully started. Keep very early
+			// UI requests alive until that safety window has passed.
+			delay := time.Until(startedAt.Add(11 * time.Second))
+			if delay > 0 {
+				time.AfterFunc(delay, func() { close(restartRequested) })
+				return
+			}
+			close(restartRequested)
+		})
+	}
+	serverUI, err := web.New(cfg, database, cipher, updater, softwareUpdates, logger, requestRestart)
 	if err != nil {
 		return err
 	}
@@ -133,6 +150,12 @@ func run(logger *slog.Logger) error {
 			return err
 		}
 		return nil
+	case <-restartRequested:
+		logger.Info("container restart requested")
+		stop()
+		shutdownCtx, cancel := context.WithTimeout(context.Background(), cfg.ShutdownTimeout)
+		defer cancel()
+		return httpServer.Shutdown(shutdownCtx)
 	case <-appCtx.Done():
 		logger.Info("shutdown requested")
 		shutdownCtx, cancel := context.WithTimeout(context.Background(), cfg.ShutdownTimeout)