forked from mqliang/kubernetes
/
detect.go
271 lines (238 loc) · 7.73 KB
/
detect.go
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/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 zoo
import (
"fmt"
"math"
"net/url"
"strconv"
"strings"
"sync"
"sync/atomic"
"time"
"github.com/gogo/protobuf/proto"
log "github.com/golang/glog"
"github.com/mesos/mesos-go/detector"
mesos "github.com/mesos/mesos-go/mesosproto"
)
const (
// prefix for nodes listed at the ZK URL path
nodePrefix = "info_"
defaultMinDetectorCyclePeriod = 1 * time.Second
)
// reasonable default for a noop change listener
var ignoreChanged = detector.OnMasterChanged(func(*mesos.MasterInfo) {})
// Detector uses ZooKeeper to detect new leading master.
type MasterDetector struct {
client *Client
leaderNode string
// for one-time zk client initiation
bootstrap sync.Once
// latch: only install, at most, one ignoreChanged listener; see MasterDetector.Detect
ignoreInstalled int32
// detection should not signal master change listeners more frequently than this
minDetectorCyclePeriod time.Duration
}
// Internal constructor function
func NewMasterDetector(zkurls string) (*MasterDetector, error) {
zkHosts, zkPath, err := parseZk(zkurls)
if err != nil {
log.Fatalln("Failed to parse url", err)
return nil, err
}
client, err := newClient(zkHosts, zkPath)
if err != nil {
return nil, err
}
detector := &MasterDetector{
client: client,
minDetectorCyclePeriod: defaultMinDetectorCyclePeriod,
}
log.V(2).Infoln("Created new detector, watching ", zkHosts, zkPath)
return detector, nil
}
func parseZk(zkurls string) ([]string, string, error) {
u, err := url.Parse(zkurls)
if err != nil {
log.V(1).Infof("failed to parse url: %v", err)
return nil, "", err
}
if u.Scheme != "zk" {
return nil, "", fmt.Errorf("invalid url scheme for zk url: '%v'", u.Scheme)
}
return strings.Split(u.Host, ","), u.Path, nil
}
// returns a chan that, when closed, indicates termination of the detector
func (md *MasterDetector) Done() <-chan struct{} {
return md.client.stopped()
}
func (md *MasterDetector) Cancel() {
md.client.stop()
}
//TODO(jdef) execute async because we don't want to stall our client's event loop? if so
//then we also probably want serial event delivery (aka. delivery via a chan) but then we
//have to deal with chan buffer sizes .. ugh. This is probably the least painful for now.
func (md *MasterDetector) childrenChanged(zkc *Client, path string, obs detector.MasterChanged) {
log.V(2).Infof("fetching children at path '%v'", path)
list, err := zkc.list(path)
if err != nil {
log.Warning(err)
return
}
md.notifyMasterChanged(path, list, obs)
md.notifyAllMasters(path, list, obs)
}
func (md *MasterDetector) notifyMasterChanged(path string, list []string, obs detector.MasterChanged) {
topNode := selectTopNode(list)
if md.leaderNode == topNode {
log.V(2).Infof("ignoring children-changed event, leader has not changed: %v", path)
return
}
log.V(2).Infof("changing leader node from %s -> %s", md.leaderNode, topNode)
md.leaderNode = topNode
var masterInfo *mesos.MasterInfo
if md.leaderNode != "" {
var err error
if masterInfo, err = md.pullMasterInfo(path, topNode); err != nil {
log.Errorln(err.Error())
}
}
log.V(2).Infof("detected master info: %+v", masterInfo)
logPanic(func() { obs.OnMasterChanged(masterInfo) })
}
// logPanic safely executes the given func, recovering from and logging a panic if one occurs.
func logPanic(f func()) {
defer func() {
if r := recover(); r != nil {
log.Errorf("recovered from client panic: %v", r)
}
}()
f()
}
func (md *MasterDetector) pullMasterInfo(path, node string) (*mesos.MasterInfo, error) {
data, err := md.client.data(fmt.Sprintf("%s/%s", path, node))
if err != nil {
return nil, fmt.Errorf("failed to retrieve leader data: %v", err)
}
masterInfo := &mesos.MasterInfo{}
err = proto.Unmarshal(data, masterInfo)
if err != nil {
return nil, fmt.Errorf("failed to unmarshall MasterInfo data from zookeeper: %v", err)
}
return masterInfo, nil
}
func (md *MasterDetector) notifyAllMasters(path string, list []string, obs detector.MasterChanged) {
all, ok := obs.(detector.AllMasters)
if !ok {
// not interested in entire master list
return
}
masters := []*mesos.MasterInfo{}
for _, node := range list {
info, err := md.pullMasterInfo(path, node)
if err != nil {
log.Errorln(err.Error())
} else {
masters = append(masters, info)
}
}
log.V(2).Infof("notifying of master membership change: %+v", masters)
logPanic(func() { all.UpdatedMasters(masters) })
}
// the first call to Detect will kickstart a connection to zookeeper. a nil change listener may
// be spec'd, result of which is a detector that will still listen for master changes and record
// leaderhip changes internally but no listener would be notified. Detect may be called more than
// once, and each time the spec'd listener will be added to the list of those receiving notifications.
func (md *MasterDetector) Detect(f detector.MasterChanged) (err error) {
// kickstart zk client connectivity
md.bootstrap.Do(func() { go md.client.connect() })
if f == nil {
// only ever install, at most, one ignoreChanged listener. multiple instances of it
// just consume resources and generate misleading log messages.
if !atomic.CompareAndSwapInt32(&md.ignoreInstalled, 0, 1) {
return
}
f = ignoreChanged
}
go md.detect(f)
return nil
}
func (md *MasterDetector) detect(f detector.MasterChanged) {
detectLoop:
for {
started := time.Now()
select {
case <-md.Done():
return
case <-md.client.connections():
// we let the golang runtime manage our listener list for us, in form of goroutines that
// callback to the master change notification listen func's
if watchEnded, err := md.client.watchChildren(currentPath, ChildWatcher(func(zkc *Client, path string) {
md.childrenChanged(zkc, path, f)
})); err == nil {
log.V(2).Infoln("detector listener installed")
select {
case <-watchEnded:
if md.leaderNode != "" {
log.V(1).Infof("child watch ended, signaling master lost")
md.leaderNode = ""
f.OnMasterChanged(nil)
}
case <-md.client.stopped():
return
}
} else {
log.V(1).Infof("child watch ended with error: %v", err)
continue detectLoop
}
}
// rate-limit master changes
if elapsed := time.Now().Sub(started); elapsed > 0 {
log.V(2).Infoln("resting before next detection cycle")
select {
case <-md.Done():
return
case <-time.After(md.minDetectorCyclePeriod - elapsed): // noop
}
}
}
}
func selectTopNode(list []string) (node string) {
var leaderSeq uint64 = math.MaxUint64
for _, v := range list {
if !strings.HasPrefix(v, nodePrefix) {
continue // only care about participants
}
seqStr := strings.TrimPrefix(v, nodePrefix)
seq, err := strconv.ParseUint(seqStr, 10, 64)
if err != nil {
log.Warningf("unexpected zk node format '%s': %v", seqStr, err)
continue
}
if seq < leaderSeq {
leaderSeq = seq
node = v
}
}
if node == "" {
log.V(3).Infoln("No top node found.")
} else {
log.V(3).Infof("Top node selected: '%s'", node)
}
return node
}