fix(registry): contrib/registry/zookeeper ephemeral nodes handling after restart (#2245)

contrib/registry/zookeeper/register.go

@@ -135,12 +135,20 @@ func (r *Registry) Watch(ctx context.Context, serviceName string) (registry.Watc
 
 // ensureName ensure node exists, if not exist, create and set data
 func (r *Registry) ensureName(path string, data []byte, flags int32) error {
-	exists, _, err := r.conn.Exists(path)
+	exists, stat, err := r.conn.Exists(path)
 	if err != nil {
 		return err
 	}
+	// ephemeral nodes handling after restart
+	// fixes a race condition if the server crashes without using CreateProtectedEphemeralSequential()
+	if flags&zk.FlagEphemeral == zk.FlagEphemeral {
+		err = r.conn.Delete(path, stat.Version)
+		if err != nil && err != zk.ErrNoNode {
+			return err
+		}
+		exists = false
+	}
 	if !exists {
-		var err error
 		if len(r.opts.user) > 0 && len(r.opts.password) > 0 {
 			_, err = r.conn.Create(path, data, flags, zk.DigestACL(zk.PermAll, r.opts.user, r.opts.password))
 		} else {