Fix etcd watch regression in IAM subsystem (#8224)

Fixes #8223

cmd/iam-etcd-store.go

@@ -503,23 +503,29 @@ func (ies *IAMEtcdStore) deleteGroupInfo(name string) error {
 
 func (ies *IAMEtcdStore) watch(sys *IAMSys) {
 	watchEtcd := func() {
-		// Refresh IAMSys with etcd watch.
 		for {
+		outerLoop:
+			// Refresh IAMSys with etcd watch.
 			watchCh := ies.client.Watch(context.Background(),
 				iamConfigPrefix, etcd.WithPrefix(), etcd.WithKeysOnly())
+			for {
 				select {
 				case <-GlobalServiceDoneCh:
 					return
 				case watchResp, ok := <-watchCh:
 					if !ok {
 						time.Sleep(1 * time.Second)
-					continue
+						// Upon an error on watch channel
+						// re-init the watch channel.
+						goto outerLoop
 					}
 					if err := watchResp.Err(); err != nil {
 						logger.LogIf(context.Background(), err)
 						// log and retry.
 						time.Sleep(1 * time.Second)
-					continue
+						// Upon an error on watch channel
+						// re-init the watch channel.
+						goto outerLoop
 					}
 					for _, event := range watchResp.Events {
 						sys.Lock()
@@ -529,6 +535,7 @@ func (ies *IAMEtcdStore) watch(sys *IAMSys) {
 				}
 			}
 		}
+	}
 	go watchEtcd()
 }