etcdutil, leadership: make more high availability

Signed-off-by: lhy1024 <[email protected]>

pkg/election/leadership.go

@@ -18,6 +18,7 @@ import (
 	"context"
 	"sync"
 	"sync/atomic"
+	"time"
 
 	"github.com/pingcap/failpoint"
 	"github.com/pingcap/kvproto/pkg/pdpb"
@@ -182,26 +183,49 @@ func (ls *Leadership) Watch(serverCtx context.Context, revision int64) {
 	if ls == nil {
 		return
 	}
+	lastHealthyTime := time.Now()
 	watcher := clientv3.NewWatcher(ls.client)
 	defer watcher.Close()
-	ctx, cancel := context.WithCancel(serverCtx)
-	defer cancel()
-	// The revision is the revision of last modification on this key.
-	// If the revision is compacted, will meet required revision has been compacted error.
-	// In this case, use the compact revision to re-watch the key.
 	for {
 		failpoint.Inject("delayWatcher", nil)
-		rch := watcher.Watch(ctx, ls.leaderKey, clientv3.WithRev(revision))
-		for wresp := range rch {
+		// In order to prevent a watch stream being stuck in a partitioned node,
+		// make sure to wrap context with "WithRequireLeader".
+		watchChanCtx, watchChanCancel := context.WithCancel(clientv3.WithRequireLeader(serverCtx))
+		defer watchChanCancel()
+
+		// when etcd is not available, the watcher.Watch will block.
+		// so we check the etcd availability first.
+		if _, err := etcdutil.EtcdKVGet(ls.client, ls.leaderKey); err != nil {
+			// If the watcher is unhealthy for more than 60 seconds, we should exit.
+			if time.Since(lastHealthyTime) > 60*time.Second {
+				log.Error("leadership watcher is unhealthy",
+					zap.Int64("revision", revision),
+					zap.String("leader-key", ls.leaderKey),
+					zap.String("purpose", ls.purpose))
+				return
+			}
+			// If the watcher is unhealthy, we should cancel the watchChan and retry.
+			// Because the etcdutil.EtcdKVGet has a timeout, we don't need to sleep here.
+			watchChanCancel()
+			continue
+		}
+		lastHealthyTime = time.Now()
+		watchChan := watcher.Watch(watchChanCtx, ls.leaderKey, clientv3.WithRev(revision))
+
+		select {
+		case <-serverCtx.Done():
+			// server closed, return
+			return
+		case wresp := <-watchChan:
 			// meet compacted error, use the compact revision.
 			if wresp.CompactRevision != 0 {
 				log.Warn("required revision has been compacted, use the compact revision",
 					zap.Int64("required-revision", revision),
 					zap.Int64("compact-revision", wresp.CompactRevision))
 				revision = wresp.CompactRevision
-				break
-			}
-			if wresp.Canceled {
+				watchChanCancel()
+				continue
+			} else if wresp.Err() != nil { // wresp.Err() contains CompactRevision not equal to 0
 				log.Error("leadership watcher is canceled with",
 					zap.Int64("revision", revision),
 					zap.String("leader-key", ls.leaderKey),
@@ -213,19 +237,15 @@ func (ls *Leadership) Watch(serverCtx context.Context, revision int64) {
 			for _, ev := range wresp.Events {
 				if ev.Type == mvccpb.DELETE {
 					log.Info("current leadership is deleted",
+						zap.Int64("revision", wresp.Header.Revision),
 						zap.String("leader-key", ls.leaderKey),
 						zap.String("purpose", ls.purpose))
 					return
 				}
 			}
+			revision = wresp.Header.Revision + 1
 		}
-
-		select {
-		case <-ctx.Done():
-			// server closed, return
-			return
-		default:
-		}
+		watchChanCancel()
 	}
 }
 

pkg/mcs/resourcemanager/server/server.go

@@ -264,7 +264,7 @@ func (s *Server) initClient() error {
 	if err != nil {
 		return err
 	}
-	s.etcdClient, s.httpClient, err = etcdutil.CreateClients(tlsConfig, []url.URL(u)[0])
+	s.etcdClient, s.httpClient, err = etcdutil.CreateClients(s.ctx, tlsConfig, []url.URL(u))
 	return err
 }
 

pkg/mcs/tso/server/server.go

@@ -386,7 +386,7 @@ func (s *Server) initClient() error {
 	if err != nil {
 		return err
 	}
-	s.etcdClient, s.httpClient, err = etcdutil.CreateClients(tlsConfig, s.backendUrls[0])
+	s.etcdClient, s.httpClient, err = etcdutil.CreateClients(s.ctx, tlsConfig, s.backendUrls)
 	return err
 }