fix panic from keyring raft entries being written during upgrade (#14821)

During an upgrade to Nomad 1.4.0, if a server running 1.4.0 becomes the leader
before one of the 1.3.x servers, the old server will crash because the keyring
is initialized and writes a raft entry.

Wait until all members are on a version that supports the keyring before
initializing it.

.changelog/14821.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+keyring: Fixed a panic that can occur during upgrades to 1.4.0 when initializing the keyring
+```

nomad/encrypter.go

@@ -277,6 +277,9 @@ func (e *Encrypter) activeKeySetLocked() (*keyset, error) {
 	if err != nil {
 		return nil, err
 	}
+	if keyMeta == nil {
+		return nil, fmt.Errorf("keyring has not been initialized yet")
+	}
 
 	return e.keysetByIDLocked(keyMeta.KeyID)
 }

nomad/leader.go

@@ -294,10 +294,7 @@ func (s *Server) establishLeadership(stopCh chan struct{}) error {
 	schedulerConfig := s.getOrCreateSchedulerConfig()
 
 	// Create the first root key if it doesn't already exist
-	err := s.initializeKeyring()
-	if err != nil {
-		return err
-	}
+	go s.initializeKeyring(stopCh)
 
 	// Initialize the ClusterID
 	_, _ = s.ClusterID()
@@ -1966,43 +1963,66 @@ func (s *Server) getOrCreateSchedulerConfig() *structs.SchedulerConfiguration {
 	return config
 }
 
+var minVersionKeyring = version.Must(version.NewVersion("1.4.0"))
+
 // initializeKeyring creates the first root key if the leader doesn't
 // already have one. The metadata will be replicated via raft and then
 // the followers will get the key material from their own key
 // replication.
-func (s *Server) initializeKeyring() error {
+func (s *Server) initializeKeyring(stopCh <-chan struct{}) {
+
+	logger := s.logger.Named("keyring")
 
 	store := s.fsm.State()
 	keyMeta, err := store.GetActiveRootKeyMeta(nil)
 	if err != nil {
-		return err
+		logger.Error("failed to get active key: %v", err)
+		return
 	}
 	if keyMeta != nil {
-		return nil
+		return
 	}
 
-	s.logger.Named("core").Trace("initializing keyring")
+	logger.Trace("verifying cluster is ready to initialize keyring")
+	for {
+		select {
+		case <-stopCh:
+			return
+		default:
+		}
+		if ServersMeetMinimumVersion(s.serf.Members(), minVersionKeyring, true) {
+			break
+		}
+	}
+	// we might have lost leadershuip during the version check
+	if !s.IsLeader() {
+		return
+	}
+
+	logger.Trace("initializing keyring")
 
 	rootKey, err := structs.NewRootKey(structs.EncryptionAlgorithmAES256GCM)
 	rootKey.Meta.SetActive()
 	if err != nil {
-		return fmt.Errorf("could not initialize keyring: %v", err)
+		logger.Error("could not initialize keyring: %v", err)
+		return
 	}
 
 	err = s.encrypter.AddKey(rootKey)
 	if err != nil {
-		return fmt.Errorf("could not add initial key to keyring: %v", err)
+		logger.Error("could not add initial key to keyring: %v", err)
+		return
 	}
 
 	if _, _, err = s.raftApply(structs.RootKeyMetaUpsertRequestType,
 		structs.KeyringUpdateRootKeyMetaRequest{
 			RootKeyMeta: rootKey.Meta,
 		}); err != nil {
-		return fmt.Errorf("could not initialize keyring: %v", err)
+		logger.Error("could not initialize keyring: %v", err)
+		return
 	}
 
-	s.logger.Named("core").Info("initialized keyring", "id", rootKey.Meta.KeyID)
-	return nil
+	logger.Info("initialized keyring", "id", rootKey.Meta.KeyID)
 }
 
 func (s *Server) generateClusterID() (string, error) {

nomad/plan_apply_test.go

@@ -243,7 +243,7 @@ func TestPlanApply_applyPlanWithNormalizedAllocs(t *testing.T) {
 	ci.Parallel(t)
 
 	s1, cleanupS1 := TestServer(t, func(c *Config) {
-		c.Build = "0.9.2"
+		c.Build = "1.4.0"
 	})
 	defer cleanupS1()
 	testutil.WaitForLeader(t, s1.RPC)

nomad/worker_test.go

@@ -488,7 +488,7 @@ func TestWorker_SubmitPlanNormalizedAllocations(t *testing.T) {
 	s1, cleanupS1 := TestServer(t, func(c *Config) {
 		c.NumSchedulers = 0
 		c.EnabledSchedulers = []string{structs.JobTypeService}
-		c.Build = "0.9.2"
+		c.Build = "1.4.0"
 	})
 	defer cleanupS1()
 	testutil.WaitForLeader(t, s1.RPC)