add sync_status field to containers table

internal/machine/docker/manager.go

@@ -20,6 +20,12 @@ const (
 	EventsDebounceInterval = 100 * time.Millisecond
 	// SyncInterval defines a regular interval to sync containers to the cluster store.
 	SyncInterval = 30 * time.Second
+
+	// SyncStatusSynced indicates that a container record is synchronised with the Docker state.
+	SyncStatusSynced = "synced"
+	// SyncStatusOutdated indicates that a container record may be outdated, for example, due to being unable
+	// to retrieve the container's state from the Docker daemon or when the machine is being stopped or restarted.
+	SyncStatusOutdated = "outdated"
 )
 
 type Manager struct {
@@ -91,6 +97,7 @@ func (d *Manager) WatchAndSyncContainers(ctx context.Context, store *store.Store
 		select {
 		case e := <-eventCh:
 			switch e.Action {
+			// Actions that may trigger a container state change.
 			case events.ActionStart,
 				events.ActionStop,
 				events.ActionPause,

internal/machine/network.go

@@ -188,16 +188,15 @@ func (nc *networkController) prepareAndWatchDocker(ctx context.Context) error {
 	}
 
 	if err = manager.EnsureUncloudNetwork(ctx, nc.state.Network.Subnet); err != nil {
-		return err
+		return fmt.Errorf("ensure Docker network: %w", err)
 	}
 	slog.Info("Docker network configured.")
 
-	slog.Info("Watching Docker containers and syncing them to the cluster store.")
+	slog.Info("Watching Docker containers and syncing them to cluster store.")
 	// Retry to watch and sync containers until the context is done.
 	boff := backoff.WithContext(backoff.NewExponentialBackOff(
 		backoff.WithInitialInterval(100*time.Millisecond),
 		backoff.WithMaxInterval(5*time.Second),
-		// Retry indefinitely.
 		backoff.WithMaxElapsedTime(0),
 	), ctx)
 	watchAndSync := func() error {

internal/machine/store/schema.sql

@@ -23,6 +23,8 @@ CREATE TABLE containers
     machine_id   TEXT NOT NULL DEFAULT '',
     service_id   TEXT AS (json_extract(container, '$.Labels."uncloud.service.id"')),
     service_name TEXT AS (json_extract(container, '$.Labels."uncloud.service.name"')),
+    -- sync_status indicates if the record reflects the actual Docker state of the container.
+    sync_status  TEXT NOT NULL DEFAULT '',
     -- updated_at is the last time the record was updated.
     updated_at   TIMESTAMP NOT NULL DEFAULT '1970-01-01 00:00:00'
 );