Add more metrics around connection buffers

sync3/connmap.go

@@ -5,6 +5,7 @@ import (
 	"time"
 
 	"github.com/ReneKroon/ttlcache/v2"
+	"github.com/prometheus/client_golang/prometheus"
 )
 
 // ConnMap stores a collection of Conns.
@@ -15,10 +16,15 @@ type ConnMap struct {
 	userIDToConn map[string][]*Conn
 	connIDToConn map[string]*Conn
 
+	numConns prometheus.Gauge
+	// counters for reasons why connections have expired
+	expiryTimedOutCounter   prometheus.Counter
+	expiryBufferFullCounter prometheus.Counter
+
 	mu *sync.Mutex
 }
 
-func NewConnMap() *ConnMap {
+func NewConnMap(enablePrometheus bool) *ConnMap {
 	cm := &ConnMap{
 		userIDToConn: make(map[string][]*Conn),
 		connIDToConn: make(map[string]*Conn),
@@ -27,17 +33,61 @@ func NewConnMap() *ConnMap {
 	}
 	cm.cache.SetTTL(30 * time.Minute) // TODO: customisable
 	cm.cache.SetExpirationCallback(cm.closeConnExpires)
+
+	if enablePrometheus {
+		cm.expiryTimedOutCounter = prometheus.NewCounter(prometheus.CounterOpts{
+			Namespace: "sliding_sync",
+			Subsystem: "api",
+			Name:      "expiry_conn_timed_out",
+			Help:      "Counter of expired API connections due to reaching TTL limit",
+		})
+		prometheus.MustRegister(cm.expiryTimedOutCounter)
+		cm.expiryBufferFullCounter = prometheus.NewCounter(prometheus.CounterOpts{
+			Namespace: "sliding_sync",
+			Subsystem: "api",
+			Name:      "expiry_conn_buffer_full",
+			Help:      "Counter of expired API connections due to reaching buffer update limit",
+		})
+		prometheus.MustRegister(cm.expiryBufferFullCounter)
+		cm.numConns = prometheus.NewGauge(prometheus.GaugeOpts{
+			Namespace: "sliding_sync",
+			Subsystem: "api",
+			Name:      "num_active_conns",
+			Help:      "Number of active sliding sync connections.",
+		})
+		prometheus.MustRegister(cm.numConns)
+	}
 	return cm
 }
 
 func (m *ConnMap) Teardown() {
 	m.cache.Close()
+
+	if m.numConns != nil {
+		prometheus.Unregister(m.numConns)
+	}
+	if m.expiryBufferFullCounter != nil {
+		prometheus.Unregister(m.expiryBufferFullCounter)
+	}
+	if m.expiryTimedOutCounter != nil {
+		prometheus.Unregister(m.expiryTimedOutCounter)
+	}
 }
 
-func (m *ConnMap) Len() int {
+// UpdateMetrics recalculates the number of active connections. Do this when you think there is a change.
+func (m *ConnMap) UpdateMetrics() {
 	m.mu.Lock()
 	defer m.mu.Unlock()
-	return len(m.connIDToConn)
+	m.updateMetrics(len(m.connIDToConn))
+}
+
+// updateMetrics is like UpdateMetrics but doesn't touch connIDToConn and hence need a lock. We use this internally
+// when we need to update the metric and already have the lock held, as calling UpdateMetrics would deadlock.
+func (m *ConnMap) updateMetrics(numConns int) {
+	if m.numConns == nil {
+		return
+	}
+	m.numConns.Set(float64(numConns))
 }
 
 // Conns return all connections for this user|device
@@ -64,8 +114,9 @@ func (m *ConnMap) Conn(cid ConnID) *Conn {
 		return conn
 	}
 	// e.g buffer exceeded, close it and remove it from the cache
-	logger.Trace().Str("conn", cid.String()).Msg("closing connection due to dead connection (buffer full)")
+	logger.Info().Str("conn", cid.String()).Msg("closing connection due to dead connection (buffer full)")
 	m.closeConn(conn)
+	m.expiryBufferFullCounter.Inc()
 	return nil
 }
 
@@ -92,6 +143,7 @@ func (m *ConnMap) CreateConn(cid ConnID, newConnHandler func() ConnHandler) (*Co
 	m.cache.Set(cid.String(), conn)
 	m.connIDToConn[cid.String()] = conn
 	m.userIDToConn[cid.UserID] = append(m.userIDToConn[cid.UserID], conn)
+	m.updateMetrics(len(m.connIDToConn))
 	return conn, true
 }
 
@@ -121,7 +173,8 @@ func (m *ConnMap) closeConnExpires(connID string, value interface{}) {
 	m.mu.Lock()
 	defer m.mu.Unlock()
 	conn := value.(*Conn)
-	logger.Trace().Str("conn", connID).Msg("closing connection due to expired TTL in cache")
+	logger.Info().Str("conn", connID).Msg("closing connection due to expired TTL in cache")
+	m.expiryTimedOutCounter.Inc()
 	m.closeConn(conn)
 }
 
@@ -147,4 +200,5 @@ func (m *ConnMap) closeConn(conn *Conn) {
 	m.userIDToConn[conn.UserID] = conns
 	// remove user cache listeners etc
 	h.Destroy()
+	m.updateMetrics(len(m.connIDToConn))
 }

sync3/handler/handler.go

@@ -59,7 +59,6 @@ type SyncLiveHandler struct {
 	GlobalCache            *caches.GlobalCache
 	maxPendingEventUpdates int
 
-	numConns     prometheus.Gauge
 	setupHistVec *prometheus.HistogramVec
 	histVec      *prometheus.HistogramVec
 	slowReqs     prometheus.Counter
@@ -74,7 +73,7 @@ func NewSync3Handler(
 		V2:                     v2Client,
 		Storage:                store,
 		V2Store:                storev2,
-		ConnMap:                sync3.NewConnMap(),
+		ConnMap:                sync3.NewConnMap(enablePrometheus),
 		userCaches:             &sync.Map{},
 		Dispatcher:             sync3.NewDispatcher(),
 		GlobalCache:            caches.NewGlobalCache(store),
@@ -128,9 +127,6 @@ func (h *SyncLiveHandler) Teardown() {
 	h.V2Sub.Teardown()
 	h.EnsurePoller.Teardown()
 	h.ConnMap.Teardown()
-	if h.numConns != nil {
-		prometheus.Unregister(h.numConns)
-	}
 	if h.setupHistVec != nil {
 		prometheus.Unregister(h.setupHistVec)
 	}
@@ -142,20 +138,7 @@ func (h *SyncLiveHandler) Teardown() {
 	}
 }
 
-func (h *SyncLiveHandler) updateMetrics() {
-	if h.numConns == nil {
-		return
-	}
-	h.numConns.Set(float64(h.ConnMap.Len()))
-}
-
 func (h *SyncLiveHandler) addPrometheusMetrics() {
-	h.numConns = prometheus.NewGauge(prometheus.GaugeOpts{
-		Namespace: "sliding_sync",
-		Subsystem: "api",
-		Name:      "num_active_conns",
-		Help:      "Number of active sliding sync connections.",
-	})
 	h.setupHistVec = prometheus.NewHistogramVec(prometheus.HistogramOpts{
 		Namespace: "sliding_sync",
 		Subsystem: "api",
@@ -176,7 +159,6 @@ func (h *SyncLiveHandler) addPrometheusMetrics() {
 		Name:      "slow_requests",
 		Help:      "Counter of slow (>=50s) requests, initial or otherwise.",
 	})
-	prometheus.MustRegister(h.numConns)
 	prometheus.MustRegister(h.setupHistVec)
 	prometheus.MustRegister(h.histVec)
 	prometheus.MustRegister(h.slowReqs)
@@ -398,7 +380,7 @@ func (h *SyncLiveHandler) setupConnection(req *http.Request, syncReq *sync3.Requ
 	}
 
 	pid := sync2.PollerID{UserID: token.UserID, DeviceID: token.DeviceID}
-  log.Trace().Any("pid", pid).Msg("checking poller exists and is running")
+	log.Trace().Any("pid", pid).Msg("checking poller exists and is running")
 	h.EnsurePoller.EnsurePolling(req.Context(), pid, token.AccessTokenHash)
 	log.Trace().Msg("poller exists and is running")
 	// this may take a while so if the client has given up (e.g timed out) by this point, just stop.
@@ -421,7 +403,7 @@ func (h *SyncLiveHandler) setupConnection(req *http.Request, syncReq *sync3.Requ
 	}
 
 	// once we have the conn, make sure our metrics are correct
-	defer h.updateMetrics()
+	defer h.ConnMap.UpdateMetrics()
 
 	// Now the v2 side of things are running, we can make a v3 live sync conn
 	// NB: this isn't inherently racey (we did the check for an existing conn before EnsurePolling)