leases: Add metrics to etcd leases

This patch adds four metrics to the `leases` package for easier
debugging.

lease/lessor.go

@@ -233,6 +233,8 @@ func (le *lessor) Grant(id LeaseID, ttl int64) (*Lease, error) {
 	heap.Push(&le.leaseHeap, item)
 	l.persistTo(le.b)
 
+	leaseTotalTTLs.Observe(float64(l.ttl))
+	leaseGranted.Inc()
 	return l, nil
 }
 
@@ -271,6 +273,8 @@ func (le *lessor) Revoke(id LeaseID) error {
 	le.b.BatchTx().UnsafeDelete(leaseBucketName, int64ToBytes(int64(l.ID)))
 
 	txn.End()
+
+	leaseRevoked.Inc()
 	return nil
 }
 
@@ -315,6 +319,8 @@ func (le *lessor) Renew(id LeaseID) (int64, error) {
 	l.refresh(0)
 	item := &LeaseWithTime{id: l.ID, expiration: l.expiry.UnixNano()}
 	heap.Push(&le.leaseHeap, item)
+
+	leaseRenewed.Inc()
 	return l.ttl, nil
 }
 

lease/metrics.go

@@ -0,0 +1,59 @@
+// Copyright 2018 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package lease
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+var (
+	leaseGranted = prometheus.NewCounter(prometheus.CounterOpts{
+		Namespace: "etcd_debugging",
+		Subsystem: "lease",
+		Name:      "granted_total",
+		Help:      "The total number of granted leases.",
+	})
+
+	leaseRevoked = prometheus.NewCounter(prometheus.CounterOpts{
+		Namespace: "etcd_debugging",
+		Subsystem: "lease",
+		Name:      "revoked_total",
+		Help:      "The total number of revoked leases.",
+	})
+
+	leaseRenewed = prometheus.NewCounter(prometheus.CounterOpts{
+		Namespace: "etcd_debugging",
+		Subsystem: "lease",
+		Name:      "renewed_total",
+		Help:      "The number of renewed leases seen by the leader.",
+	})
+
+	leaseTotalTTLs = prometheus.NewHistogram(
+		prometheus.HistogramOpts{
+			Namespace: "etcd_debugging",
+			Subsystem: "lease",
+			Name:      "ttl_total",
+			Help:      "Bucketed histogram of lease TTLs.",
+			// 1 second -> 3 months
+			Buckets: prometheus.ExponentialBuckets(1, 2, 24),
+		})
+)
+
+func init() {
+	prometheus.MustRegister(leaseGranted)
+	prometheus.MustRegister(leaseRevoked)
+	prometheus.MustRegister(leaseRenewed)
+	prometheus.MustRegister(leaseTotalTTLs)
+}