学习 etcd watch api

测试代码

func Test_watch(t *testing.T) {    ec, _ := NewEtcdClient([]string{"http://127.0.0.1:2379"})    cli := ec.getEtcdAPI()    go func() {        watcher := cli.Watcher("/a", &client.WatcherOptions{            Recursive: true,        })        for {            resp, err := watcher.Next(context.Background())            fmt.Println(resp)            fmt.Println(err)        }    }()    cli.Set(context.Background(), "/a/b", "a-b", &client.SetOptions{})    time.Sleep(1 * time.Second)    cli.Set(context.Background(), "/a/b/c", "a-b-c", &client.SetOptions{})    time.Sleep(1 * time.Second)    cli.Set(context.Background(), "/a/d", "a-d", &client.SetOptions{})    time.Sleep(1 * time.Second)    cli.Delete(context.Background(), "/a/b/c", &client.DeleteOptions{})    time.Sleep(1 * time.Second)    cli.Delete(context.Background(), "/a/b", &client.DeleteOptions{})    time.Sleep(1 * time.Second)}

结果是

{"action":"set","node":{"key":"/a/b","value":"a-b","modifiedIndex":479128,"createdIndex":479128},"prevNode":{"key":"/a/b","value":"a-b","modifiedIndex":479126,"createdIndex":479126}}&{set {Key: /a/b, CreatedIndex: 479128, ModifiedIndex: 479128, TTL: 0} {Key: /a/b, CreatedIndex: 479126, ModifiedIndex: 479126, TTL: 0} 479127}{"action":"set","node":{"key":"/a/d","value":"a-d","modifiedIndex":479129,"createdIndex":479129},"prevNode":{"key":"/a/d","value":"a-d","modifiedIndex":479127,"createdIndex":479127}}&{set {Key: /a/d, CreatedIndex: 479129, ModifiedIndex: 479129, TTL: 0} {Key: /a/d, CreatedIndex: 479127, ModifiedIndex: 479127, TTL: 0} 479128}{"action":"delete","node":{"key":"/a/b","modifiedIndex":479130,"createdIndex":479128},"prevNode":{"key":"/a/b","value":"a-b","modifiedIndex":479128,"createdIndex":479128}}&{delete {Key: /a/b, CreatedIndex: 479128, ModifiedIndex: 479130, TTL: 0} {Key: /a/b, CreatedIndex: 479128, ModifiedIndex: 479128, TTL: 0} 479129}

结论是

1. etcd 的 directory 类型节点可以通过设置recursive=True，watch其直接儿子的新增和删除

2. 孙子节点的新增和删除无法被感知

3. 没有加recursive=True无法感知其儿子的新增和删除

4. 新增和删除的节点会在watch消息里给出，无需再去用get拉取内容。也就是watch给的是类似binlog的增量同步消息

5. 依赖watch来增量同步，需要保证watch不丢掉中间改动。这个可以通过WatcherOptions上的AfterIndex属性来实现，Index就是etcd node的版本。etcd v2 只有节点级别的版本，v3 才有全仓库的版本。

关键字：etcd

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