[FIXED] Server peer re-add after peer-remove

server/jetstream_cluster_1_test.go

@@ -3776,6 +3776,89 @@ func TestJetStreamClusterPeerRemovalAndStreamReassignmentWithoutSpace(t *testing
 	streamCurrent(2)
 }
 
+func TestJetStreamClusterPeerRemovalAndServerBroughtBack(t *testing.T) {
+	// Speed up for this test
+	peerRemoveTimeout = 2 * time.Second
+	defer func() {
+		peerRemoveTimeout = peerRemoveTimeoutDefault
+	}()
+
+	c := createJetStreamClusterExplicit(t, "R5S", 5)
+	defer c.shutdown()
+
+	// Client based API
+	ml := c.leader()
+	nc, err := nats.Connect(ml.ClientURL(), nats.UserInfo("admin", "s3cr3t!"))
+	if err != nil {
+		t.Fatalf("Failed to create system client: %v", err)
+	}
+	defer nc.Close()
+
+	getPeersCount := func() int {
+		js := ml.getJetStream()
+		if js == nil {
+			return 0
+		}
+		js.mu.RLock()
+		defer js.mu.RUnlock()
+
+		cc := js.cluster
+		if !cc.isLeader() || cc.meta == nil {
+			return 0
+		}
+		return len(cc.meta.Peers())
+	}
+
+	checkFor(t, 2*time.Second, 250*time.Millisecond, func() error {
+		if l := getPeersCount(); l != 5 {
+			return fmt.Errorf("expected 5 peers, got %d", l)
+		}
+		return nil
+	})
+
+	// Shutdown server first.
+	rs := c.randomNonLeader()
+	rs.Shutdown()
+
+	// Peers should still remain the same, even if one server is shut down.
+	checkFor(t, 2*time.Second, 250*time.Millisecond, func() error {
+		if l := getPeersCount(); l != 5 {
+			return fmt.Errorf("expected 5 peers, got %d", l)
+		}
+		return nil
+	})
+
+	// Peer-remove after shutdown.
+	req := &JSApiMetaServerRemoveRequest{Server: rs.Name()}
+	jsreq, err := json.Marshal(req)
+	require_NoError(t, err)
+	rmsg, err := nc.Request(JSApiRemoveServer, jsreq, time.Second)
+	require_NoError(t, err)
+
+	var resp JSApiMetaServerRemoveResponse
+	require_NoError(t, json.Unmarshal(rmsg.Data, &resp))
+	if resp.Error != nil {
+		t.Fatalf("Unexpected error: %+v", resp.Error)
+	}
+
+	// Peer should be removed.
+	checkFor(t, 2*time.Second, 250*time.Millisecond, func() error {
+		if l := getPeersCount(); l != 4 {
+			return fmt.Errorf("expected 4 peers, got %d", l)
+		}
+		return nil
+	})
+
+	// Bringing back the server should re-add to peers after peer-remove timeout.
+	c.restartServer(rs)
+	checkFor(t, 5*time.Second, 250*time.Millisecond, func() error {
+		if l := getPeersCount(); l != 5 {
+			return fmt.Errorf("expected 5 peers, got %d", l)
+		}
+		return nil
+	})
+}
+
 func TestJetStreamClusterPeerExclusionTag(t *testing.T) {
 	c := createJetStreamClusterWithTemplateAndModHook(t, jsClusterTempl, "C", 3,
 		func(serverName, clusterName, storeDir, conf string) string {

server/raft.go

@@ -154,7 +154,7 @@ type raft struct {
 	qn    int             // Number of nodes needed to establish quorum
 	peers map[string]*lps // Other peers in the Raft group
 
-	removed map[string]struct{}            // Peers that were removed from the group
+	removed map[string]time.Time           // Peers that were removed from the group
 	acks    map[uint64]map[string]struct{} // Append entry responses/acks, map of entry index -> peer ID
 	pae     map[uint64]*appendEntry        // Pending append entries
 
@@ -253,6 +253,7 @@ const (
 	lostQuorumIntervalDefault      = hbIntervalDefault * 10 // 10 seconds
 	lostQuorumCheckIntervalDefault = hbIntervalDefault * 10 // 10 seconds
 	observerModeIntervalDefault    = 48 * time.Hour
+	peerRemoveTimeoutDefault       = 5 * time.Minute
 )
 
 var (
@@ -264,6 +265,7 @@ var (
 	lostQuorumInterval   = lostQuorumIntervalDefault
 	lostQuorumCheck      = lostQuorumCheckIntervalDefault
 	observerModeInterval = observerModeIntervalDefault
+	peerRemoveTimeout    = peerRemoveTimeoutDefault
 )
 
 type RaftConfig struct {
@@ -892,9 +894,9 @@ func (n *raft) ProposeAddPeer(peer string) error {
 func (n *raft) doRemovePeerAsLeader(peer string) {
 	n.Lock()
 	if n.removed == nil {
-		n.removed = map[string]struct{}{}
+		n.removed = map[string]time.Time{}
 	}
-	n.removed[peer] = struct{}{}
+	n.removed[peer] = time.Now()
 	if _, ok := n.peers[peer]; ok {
 		delete(n.peers, peer)
 		// We should decrease our cluster size since we are tracking this peer and the peer is most likely already gone.
@@ -2968,9 +2970,9 @@ func (n *raft) applyCommit(index uint64) error {
 
 			// Make sure we have our removed map.
 			if n.removed == nil {
-				n.removed = make(map[string]struct{})
+				n.removed = make(map[string]time.Time)
 			}
-			n.removed[peer] = struct{}{}
+			n.removed[peer] = time.Now()
 
 			if _, ok := n.peers[peer]; ok {
 				delete(n.peers, peer)
@@ -3085,8 +3087,13 @@ func (n *raft) adjustClusterSizeAndQuorum() {
 func (n *raft) trackPeer(peer string) error {
 	n.Lock()
 	var needPeerAdd, isRemoved bool
+	var rts time.Time
 	if n.removed != nil {
-		_, isRemoved = n.removed[peer]
+		rts, isRemoved = n.removed[peer]
+		// Removed peers can rejoin after timeout.
+		if isRemoved && time.Since(rts) >= peerRemoveTimeout {
+			isRemoved = false
+		}
 	}
 	if n.State() == Leader {
 		if lp, ok := n.peers[peer]; !ok || !lp.kp {