This adds ability to have a single node server with a system leafnode expand an existing JetStream cluster domain.

Signed-off-by: Derek Collison <derek@nats.io>

server/jetstream.go

@@ -219,7 +219,7 @@ func (s *Server) enableJetStream(cfg JetStreamConfig) error {
 	}
 
 	// If we are in clustered mode go ahead and start the meta controller.
-	if !s.standAloneMode() {
+	if !s.standAloneMode() || s.hasSolicitLeafNodeSystemShare() {
 		if err := s.enableJetStreamClustering(); err != nil {
 			return err
 		}
@@ -228,6 +228,22 @@ func (s *Server) enableJetStream(cfg JetStreamConfig) error {
 	return nil
 }
 
+// This will check if we have the a solicited leafnode that shares the system account.
+func (s *Server) hasSolicitLeafNodeSystemShare() bool {
+	sysAcc := s.SystemAccount().GetName()
+	for _, r := range s.getOpts().LeafNode.Remotes {
+		if r.LocalAccount == sysAcc {
+			for _, denySub := range r.DenyImports {
+				if subjectIsSubsetMatch(denySub, raftAllSubj) {
+					return false
+				}
+			}
+			return true
+		}
+	}
+	return false
+}
+
 func (s *Server) updateJetStreamInfoStatus(enabled bool) {
 	s.mu.Lock()
 	s.info.JetStream = enabled

server/jetstream_cluster.go

@@ -460,8 +460,13 @@ func (s *Server) enableJetStreamClustering() error {
 	s.Noticef("Starting JetStream cluster")
 	// We need to determine if we have a stable cluster name and expected number of servers.
 	s.Debugf("JetStream cluster checking for stable cluster name and peers")
-	if s.isClusterNameDynamic() || s.configuredRoutes() == 0 {
-		return errors.New("JetStream cluster requires cluster name and explicit routes")
+
+	hasLeafNodeSystemShare := s.hasSolicitLeafNodeSystemShare()
+	if s.isClusterNameDynamic() && !hasLeafNodeSystemShare {
+		return errors.New("JetStream cluster requires cluster name")
+	}
+	if s.configuredRoutes() == 0 && !hasLeafNodeSystemShare {
+		return errors.New("JetStream cluster requires configured routes or solicited leafnode for the system account")
 	}
 
 	return js.setupMetaGroup()
@@ -489,22 +494,7 @@ func (js *jetStream) setupMetaGroup() error {
 	// If we are soliciting leafnode connections and we are sharing a system account
 	// we want to move to observer mode so that we extend the solicited cluster or supercluster
 	// but do not form our own.
-	if ln := s.getOpts().LeafNode; len(ln.Remotes) > 0 {
-		sys := s.SystemAccount().GetName()
-	ENDFOR:
-		for _, r := range ln.Remotes {
-			if r.LocalAccount == sys {
-				for _, denySub := range r.DenyImports {
-					if subjectIsSubsetMatch(denySub, raftAllSubj) {
-						// raft group is denied, hence there won't be anything to observe
-						break ENDFOR
-					}
-				}
-				cfg.Observer = true
-				break ENDFOR
-			}
-		}
-	}
+	cfg.Observer = s.hasSolicitLeafNodeSystemShare()
 
 	var bootstrap bool
 	if _, err := readPeerState(storeDir); err != nil {

server/jetstream_cluster_test.go

@@ -5629,6 +5629,20 @@ func TestJetStreamClusterSuperClusterAndLeafNodesWithSharedSystemAccount(t *test
 	}
 }
 
+func TestJetStreamClusterSuperClusterAndSingleLeafNodeWithSharedSystemAccount(t *testing.T) {
+	sc := createJetStreamSuperCluster(t, 3, 2)
+	defer sc.shutdown()
+
+	ln := sc.createSingleLeafNode()
+	defer ln.Shutdown()
+
+	// We want to make sure there is only one leader and its always in the supercluster.
+	sc.waitOnLeader()
+
+	// leafnodes should have been added into the overall peer count.
+	sc.waitOnPeerCount(7)
+}
+
 func TestJetStreamClusterLeafDifferentAccounts(t *testing.T) {
 	c := createJetStreamCluster(t, jsClusterAccountsTempl, "HUB", _EMPTY_, 2, 33133, false)
 	defer c.shutdown()
@@ -6172,6 +6186,11 @@ func (sc *supercluster) createLeafNodes(clusterName string, numServers int) *clu
 	return c.createLeafNodes(clusterName, numServers)
 }
 
+func (sc *supercluster) createSingleLeafNode() *Server {
+	c := sc.randomCluster()
+	return c.createLeafNode()
+}
+
 func (sc *supercluster) leader() *Server {
 	for _, c := range sc.clusters {
 		if leader := c.leader(); leader != nil {
@@ -6423,6 +6442,17 @@ var jsClusterTemplWithLeafNode = `
 	accounts { $SYS { users = [ { user: "admin", pass: "s3cr3t!" } ] } }
 `
 
+var jsClusterTemplWithSingleLeafNode = `
+	listen: 127.0.0.1:-1
+	server_name: %s
+	jetstream: {max_mem_store: 256MB, max_file_store: 2GB, store_dir: "%s"}
+
+	{{leaf}}
+
+	# For access to system account.
+	accounts { $SYS { users = [ { user: "admin", pass: "s3cr3t!" } ] } }
+`
+
 var jsLeafFrag = `
 	leaf {
 		remotes [
@@ -6441,7 +6471,17 @@ func (c *cluster) createLeafNodesWithStartPort(clusterName string, numServers in
 	return c.createLeafNodesWithStartPortAndMQTT(clusterName, numServers, portStart, _EMPTY_)
 }
 
-func (c *cluster) createLeafNodesWithStartPortAndMQTT(clusterName string, numServers int, portStart int, mqtt string) *cluster {
+func (c *cluster) createLeafNode() *Server {
+	tmpl := c.createLeafSolicit(jsClusterTemplWithSingleLeafNode)
+	conf := fmt.Sprintf(tmpl, "LNS", createDir(c.t, JetStreamStoreDir))
+	s, o := RunServerWithConfig(createConfFile(c.t, []byte(conf)))
+	c.servers = append(c.servers, s)
+	c.opts = append(c.opts, o)
+	return s
+}
+
+// Helper to generate the leaf solicit configs.
+func (c *cluster) createLeafSolicit(tmpl string) string {
 	// Create our leafnode cluster template first.
 	var lns, lnss []string
 	for _, s := range c.servers {
@@ -6452,7 +6492,12 @@ func (c *cluster) createLeafNodesWithStartPortAndMQTT(clusterName string, numSer
 	lnc := strings.Join(lns, ", ")
 	lnsc := strings.Join(lnss, ", ")
 	lconf := fmt.Sprintf(jsLeafFrag, lnc, lnsc)
-	tmpl := strings.Replace(jsClusterTemplWithLeafNode, "{{leaf}}", lconf, 1)
+	return strings.Replace(tmpl, "{{leaf}}", lconf, 1)
+}
+
+func (c *cluster) createLeafNodesWithStartPortAndMQTT(clusterName string, numServers int, portStart int, mqtt string) *cluster {
+	// Create our leafnode cluster template first.
+	tmpl := c.createLeafSolicit(jsClusterTemplWithLeafNode)
 	tmpl = strings.Replace(tmpl, "{{mqtt}}", mqtt, 1)
 
 	pre := clusterName + "-"

server/server.go

@@ -524,7 +524,7 @@ func (s *Server) setClusterName(name string) {
 
 // Return whether the cluster name is dynamic.
 func (s *Server) isClusterNameDynamic() bool {
-	return s.getOpts().Cluster.Name == ""
+	return s.getOpts().Cluster.Name == _EMPTY_
 }
 
 // ClientURL returns the URL used to connect clients. Helpful in testing