Merge pull request #1985 from tommyulfsparre/resync

Resync state after ZooKeeper failure

util/treecache/treecache.go

@@ -19,10 +19,31 @@ import (
 	"strings"
 	"time"
 
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/common/log"
 	"github.com/samuel/go-zookeeper/zk"
 )
 
+var (
+	failureCounter = prometheus.NewCounter(prometheus.CounterOpts{
+		Namespace: "prometheus",
+		Subsystem: "treecache",
+		Name:      "zookeeper_failures_total",
+		Help:      "The total number of ZooKeeper failures.",
+	})
+	numWatchers = prometheus.NewGauge(prometheus.GaugeOpts{
+		Namespace: "prometheus",
+		Subsystem: "treecache",
+		Name:      "watcher_goroutines",
+		Help:      "The current number of watcher goroutines.",
+	})
+)
+
+func init() {
+	prometheus.MustRegister(failureCounter)
+	prometheus.MustRegister(numWatchers)
+}
+
 type ZookeeperLogger struct {
 }
 
@@ -81,6 +102,7 @@ func (tc *ZookeeperTreeCache) loop(failureMode bool) {
 	retryChan := make(chan struct{})
 
 	failure := func() {
+		failureCounter.Inc()
 		failureMode = true
 		time.AfterFunc(time.Second*10, func() {
 			retryChan <- struct{}{}
@@ -129,13 +151,19 @@ func (tc *ZookeeperTreeCache) loop(failureMode bool) {
 			}
 		case <-retryChan:
 			log.Infof("Attempting to resync state with Zookeeper")
+			previousState := &zookeeperTreeCacheNode{
+				children: tc.head.children,
+			}
 			// Reset root child nodes before traversing the Zookeeper path.
 			tc.head.children = make(map[string]*zookeeperTreeCacheNode)
-			err := tc.recursiveNodeUpdate(tc.prefix, tc.head)
-			if err != nil {
+
+			if err := tc.recursiveNodeUpdate(tc.prefix, tc.head); err != nil {
 				log.Errorf("Error during Zookeeper resync: %s", err)
+				// Revert to our previous state.
+				tc.head.children = previousState.children
 				failure()
 			} else {
+				tc.resyncState(tc.prefix, tc.head, previousState)
 				log.Infof("Zookeeper resync successful")
 				failureMode = false
 			}
@@ -199,6 +227,7 @@ func (tc *ZookeeperTreeCache) recursiveNodeUpdate(path string, node *zookeeperTr
 	}
 
 	go func() {
+		numWatchers.Inc()
 		// Pass up zookeeper events, until the node is deleted.
 		select {
 		case event := <-dataWatcher:
@@ -207,10 +236,21 @@ func (tc *ZookeeperTreeCache) recursiveNodeUpdate(path string, node *zookeeperTr
 			node.events <- event
 		case <-node.done:
 		}
+		numWatchers.Dec()
 	}()
 	return nil
 }
 
+func (tc *ZookeeperTreeCache) resyncState(path string, currentState, previousState *zookeeperTreeCacheNode) {
+	for child, previousNode := range previousState.children {
+		if currentNode, present := currentState.children[child]; present {
+			tc.resyncState(path+"/"+child, currentNode, previousNode)
+		} else {
+			tc.recursiveDelete(path+"/"+child, previousNode)
+		}
+	}
+}
+
 func (tc *ZookeeperTreeCache) recursiveDelete(path string, node *zookeeperTreeCacheNode) {
 	if !node.stopped {
 		node.done <- struct{}{}