监听etcd中的kv变化，常用来做集群中的配置下发、状态同步，非常有价值。

package mainimport ( "go.etcd.io/etcd/clientv3" "time" "fmt" "context" "go.etcd.io/etcd/mvcc/mvccpb")func main() { var ( config clientv3.Config client *clientv3.Client err error kv clientv3.KV watcher clientv3.Watcher getResp *clientv3.GetResponse watchStartRevision int64 watchRespChan <-chan clientv3.WatchResponse watchResp clientv3.WatchResponse event *clientv3.Event ) // 客户端配置 config = clientv3.Config{ Endpoints: []string{"0.0.0.0:2379"}, DialTimeout: 5 * time.Second, } // 建立连接 if client, err = clientv3.New(config); err != nil { fmt.Println(err) return } // KV kv = clientv3.NewKV(client) // 模拟etcd中KV的变化 go func() { for { kv.Put(context.TODO(), "/cron/jobs/job7", "i am job7") kv.Delete(context.TODO(), "/cron/jobs/job7") time.Sleep(1 * time.Second) } }() // 先GET到当前的值，并监听后续变化 if getResp, err = kv.Get(context.TODO(), "/cron/jobs/job7"); err != nil { fmt.Println(err) return } // 现在key是存在的 if len(getResp.Kvs) != 0 { fmt.Println("当前值:", string(getResp.Kvs[0].Value)) } // 当前etcd集群事务ID, 单调递增的（监听/cron/jobs/job7后续的变化,也就是通过监听版本变化） watchStartRevision = getResp.Header.Revision + 1 // 创建一个watcher(监听器) watcher = clientv3.NewWatcher(client) // 启动监听 fmt.Println("从该版本向后监听:", watchStartRevision) ctx, cancelFunc := context.WithCancel(context.TODO()) //5秒钟后取消 time.AfterFunc(5 * time.Second, func() { cancelFunc() }) //这里ctx感知到cancel则会关闭watcher watchRespChan = watcher.Watch(ctx, "/cron/jobs/job7", clientv3.WithRev(watchStartRevision)) // 处理kv变化事件 for watchResp = range watchRespChan { for _, event = range watchResp.Events { switch event.Type { case mvccpb.PUT: fmt.Println("修改为:", string(event.Kv.Value), "Revision:", event.Kv.CreateRevision, event.Kv.ModRevision) case mvccpb.DELETE: fmt.Println("删除了", "Revision:", event.Kv.ModRevision) } } }}

输出：

[root@bogon etcd]# go run demo8.go
当前值: i am job7
从该版本向后监听: 33
删除了 Revision: 33
修改为: i am job7 Revision: 34 34
删除了 Revision: 35
修改为: i am job7 Revision: 36 36
删除了 Revision: 37
修改为: i am job7 Revision: 38 38
删除了 Revision: 39
修改为: i am job7 Revision: 40 40
删除了 Revision: 41
[root@bogon etcd]#