feat: add resilient updates and access controls

cmd/update-agent/main.go

@@ -0,0 +1,88 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"log/slog"
+	"net"
+	"net/http"
+	"os"
+	"os/signal"
+	"path/filepath"
+	"strings"
+	"syscall"
+	"time"
+
+	"github.com/root-kdw12/hetzner-api-dyndns-records-webinterface/internal/updateagent"
+)
+
+func main() {
+	logger := slog.New(slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{Level: slog.LevelInfo}))
+	if err := run(logger); err != nil {
+		logger.Error("update agent stopped", "error", err)
+		os.Exit(1)
+	}
+}
+
+func run(logger *slog.Logger) error {
+	socket := env("UPDATE_AGENT_SOCKET", "/run/domain-control-update/agent.sock")
+	dockerSocket := env("UPDATE_DOCKER_SOCKET", "/var/run/docker.sock")
+	image := env("UPDATE_IMAGE_REPOSITORY", "git.j-mahler.de/admin/domain-control-webinterface-prod")
+	targetLabel := env("UPDATE_TARGET_LABEL", "de.j-mahler.domain-control.role=app")
+	directory := filepath.Dir(socket)
+	if err := os.MkdirAll(directory, 0o711); err != nil {
+		return err
+	}
+	if err := os.Chmod(directory, 0o711); err != nil {
+		return err
+	}
+	if err := os.Remove(socket); err != nil && !errors.Is(err, os.ErrNotExist) {
+		return err
+	}
+	listener, err := net.Listen("unix", socket)
+	if err != nil {
+		return err
+	}
+	defer listener.Close()
+	defer os.Remove(socket)
+	// The container runs as uid 0 with gid 10001. Group-only access lets the
+	// unprivileged web process connect without exposing the socket to others.
+	if err := os.Chmod(socket, 0o660); err != nil {
+		return err
+	}
+	runner := updateagent.NewDockerRunner(dockerSocket, image, targetLabel, logger)
+	controller := updateagent.NewController(runner, logger)
+	server := &http.Server{
+		Handler:           controller.Handler(),
+		ReadHeaderTimeout: 3 * time.Second,
+		ReadTimeout:       5 * time.Second,
+		WriteTimeout:      5 * time.Second,
+		IdleTimeout:       15 * time.Second,
+		MaxHeaderBytes:    8 << 10,
+	}
+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+	defer stop()
+	serverErrors := make(chan error, 1)
+	go func() {
+		logger.Info("update agent ready", "socket", socket)
+		serverErrors <- server.Serve(listener)
+	}()
+	select {
+	case err := <-serverErrors:
+		if errors.Is(err, http.ErrServerClosed) {
+			return nil
+		}
+		return err
+	case <-ctx.Done():
+		shutdownCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+		defer cancel()
+		return server.Shutdown(shutdownCtx)
+	}
+}
+
+func env(name, fallback string) string {
+	if value := strings.TrimSpace(os.Getenv(name)); value != "" {
+		return value
+	}
+	return fallback
+}