Handling a race condition better, and better error message.

go/vt/tabletmanager/agent.go

@@ -156,10 +156,11 @@ func NewActionAgent(
 
 	// try to initialize the tablet if we have to
 	if err := agent.InitTablet(port, securePort); err != nil {
-		return nil, err
+		return nil, fmt.Errorf("agent.InitTablet failed: %v", err)
 	}
 
-	// Publish and set the TargetTabletType. Not a global var since it should never be changed.
+	// Publish and set the TargetTabletType. Not a global var
+	// since it should never be changed.
 	statsTabletType := stats.NewString("TargetTabletType")
 	statsTabletType.Set(*targetTabletType)
 

go/vt/tabletmanager/init_tablet.go

@@ -97,8 +97,10 @@ func (agent *ActionAgent) InitTablet(port, securePort int) error {
 				return fmt.Errorf("CreateKeyspace(%v) failed: %v", *initKeyspace, err)
 			}
 
-			// create the shard
-			if err := topo.CreateShard(agent.TopoServer, *initKeyspace, shard); err != nil {
+			// create the shard (it may already exist if
+			// someone else just created it, this code is
+			// not protected by a lock of any kind)
+			if err := topo.CreateShard(agent.TopoServer, *initKeyspace, shard); err != nil && err != topo.ErrNodeExists {
 				return fmt.Errorf("CreateShard(%v/%v) failed: %v", *initKeyspace, shard, err)
 			}