consul: Disable tombstones as follower

consul/leader.go

@@ -50,16 +50,15 @@ func (s *Server) monitorLeadership() {
 // leaderLoop runs as long as we are the leader to run various
 // maintence activities
 func (s *Server) leaderLoop(stopCh chan struct{}) {
+	// Ensure we revoke leadership on stepdown
+	defer s.revokeLeadership()
+
 	// Fire a user event indicating a new leader
 	payload := []byte(s.config.NodeName)
 	if err := s.serfLAN.UserEvent(newLeaderEvent, payload, false); err != nil {
 		s.logger.Printf("[WARN] consul: failed to broadcast new leader event: %v", err)
 	}
 
-	// Clear the session timers on either shutdown or step down, since we
-	// are no longer responsible for session expirations.
-	defer s.clearAllSessionTimers()
-
 	// Reconcile channel is only used once initial reconcile
 	// has succeeded
 	var reconcileCh chan serf.Member
@@ -126,7 +125,7 @@ func (s *Server) establishLeadership() error {
 	// Hint the tombstone expiration timer. When we freshly establish leadership
 	// we become the authoritative timer, and so we need to start the clock
 	// on any pending GC events.
-	s.tombstoneGC.Reset()
+	s.tombstoneGC.SetEnabled(true)
 	lastIndex := s.raft.LastIndex()
 	s.tombstoneGC.Hint(lastIndex)
 	s.logger.Printf("[DEBUG] consul: reset tombstone GC to index %d", lastIndex)
@@ -154,6 +153,21 @@ func (s *Server) establishLeadership() error {
 	return nil
 }
 
+// revokeLeadership is invoked once we step down as leader.
+// This is used to cleanup any state that may be specific to a leader.
+func (s *Server) revokeLeadership() error {
+	// Disable the tombstone GC, since it is only useful as a leader
+	s.tombstoneGC.SetEnabled(false)
+
+	// Clear the session timers on either shutdown or step down, since we
+	// are no longer responsible for session expirations.
+	if err := s.clearAllSessionTimers(); err != nil {
+		s.logger.Printf("[ERR] consul: Clearing session timers failed: %v", err)
+		return err
+	}
+	return nil
+}
+
 // initializeACL is used to setup the ACLs if we are the leader
 // and need to do this.
 func (s *Server) initializeACL() error {

consul/tombstone_gc.go

@@ -23,13 +23,18 @@ type TombstoneGC struct {
 	ttl         time.Duration
 	granularity time.Duration
 
+	// enabled controls if we actually setup any timers.
+	enabled bool
+
 	// expires maps the time of expiration to the highest
 	// tombstone value that should be expired.
-	expires     map[time.Time]*expireInterval
-	expiresLock sync.Mutex
+	expires map[time.Time]*expireInterval
 
 	// expireCh is used to stream expiration
 	expireCh chan uint64
+
+	// lock is used to ensure safe access to all the fields
+	lock sync.Mutex
 }
 
 // expireInterval is used to track the maximum index
@@ -53,6 +58,7 @@ func NewTombstoneGC(ttl, granularity time.Duration) (*TombstoneGC, error) {
 	t := &TombstoneGC{
 		ttl:         ttl,
 		granularity: granularity,
+		enabled:     false,
 		expires:     make(map[time.Time]*expireInterval),
 		expireCh:    make(chan uint64, 1),
 	}
@@ -65,14 +71,25 @@ func (t *TombstoneGC) ExpireCh() <-chan uint64 {
 	return t.expireCh
 }
 
-// Reset is used to clear the TTL timers
-func (t *TombstoneGC) Reset() {
-	t.expiresLock.Lock()
-	defer t.expiresLock.Unlock()
-	for _, exp := range t.expires {
-		exp.timer.Stop()
+// SetEnabled is used to control if the tombstone GC is
+// enabled. Should only be enabled by the leader node.
+func (t *TombstoneGC) SetEnabled(enabled bool) {
+	t.lock.Lock()
+	defer t.lock.Unlock()
+	if enabled == t.enabled {
+		return
 	}
-	t.expires = make(map[time.Time]*expireInterval)
+
+	// Stop all the timers and clear
+	if !enabled {
+		for _, exp := range t.expires {
+			exp.timer.Stop()
+		}
+		t.expires = make(map[time.Time]*expireInterval)
+	}
+
+	// Update the status
+	t.enabled = enabled
 }
 
 // Hint is used to indicate that keys at the given index have been
@@ -80,8 +97,11 @@ func (t *TombstoneGC) Reset() {
 func (t *TombstoneGC) Hint(index uint64) {
 	expires := t.nextExpires()
 
-	t.expiresLock.Lock()
-	defer t.expiresLock.Unlock()
+	t.lock.Lock()
+	defer t.lock.Unlock()
+	if !t.enabled {
+		return
+	}
 
 	// Check for an existing expiration timer
 	exp, ok := t.expires[expires]
@@ -104,8 +124,8 @@ func (t *TombstoneGC) Hint(index uint64) {
 
 // PendingExpiration is used to check if any expirations are pending
 func (t *TombstoneGC) PendingExpiration() bool {
-	t.expiresLock.Lock()
-	defer t.expiresLock.Unlock()
+	t.lock.Lock()
+	defer t.lock.Unlock()
 	return len(t.expires) > 0
 }
 
@@ -120,10 +140,10 @@ func (t *TombstoneGC) nextExpires() time.Time {
 // expireTime is used to expire the entries at the given time
 func (t *TombstoneGC) expireTime(expires time.Time) {
 	// Get the maximum index and clear the entry
-	t.expiresLock.Lock()
+	t.lock.Lock()
 	exp := t.expires[expires]
 	delete(t.expires, expires)
-	t.expiresLock.Unlock()
+	t.lock.Unlock()
 
 	// Notify the expires channel
 	t.expireCh <- exp.maxIndex

consul/tombstone_gc_test.go

@@ -29,6 +29,7 @@ func TestTombstoneGC(t *testing.T) {
 	if err != nil {
 		t.Fatalf("should fail")
 	}
+	gc.SetEnabled(true)
 
 	if gc.PendingExpiration() {
 		t.Fatalf("should not be pending")
@@ -82,13 +83,14 @@ func TestTombstoneGC_Expire(t *testing.T) {
 	if err != nil {
 		t.Fatalf("should fail")
 	}
+	gc.SetEnabled(true)
 
 	if gc.PendingExpiration() {
 		t.Fatalf("should not be pending")
 	}
 
 	gc.Hint(100)
-	gc.Reset()
+	gc.SetEnabled(false)
 
 	if gc.PendingExpiration() {
 		t.Fatalf("should not be pending")