Go语言对etcd的基本操作

　　本文简单介绍Go语言对etcd v3的基本操作。

1. Import package

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import (     "github.com/coreos/etcd/clientv3"     "github.com/coreos/etcd/mvcc/mvccpb" )

 

2. Declare Variables

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var cli *clientv3.Client   var serverList = []string{     "192.168.3.102:2379",     "192.168.3.105:2379",     "192.168.3.103:2379", } var userName = "root" var password = "shiajun666" var dialTimeout = 5 var opTimeout = 5

 

3. Connect to etcd server

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var err error cli, err := clientv3.New(clientv3.Config{     Endpoints:   serverList,     DialTimeout: time.Duration(dialTimeout) * time.Second,     Username:    userName,     Password:    password, }) if err != nil {     fmt.Println("Connect etcd server failed: ", err)     return }

 

4. Get

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ctx, cancel := context.WithTimeout(context.Background(), time.Duration(opTimeout)*time.Second) defer cancel()   key := "name" resp, err := cli.Get(ctx, key) if err != nil {     fmt.Printf("Get key[%s] failed: %v\n", key, err)     return } if len(resp.Kvs) == 0 {     fmt.Printf("Key[%s] not exists.\n", key)     return }   fmt.Println("value: ", string(resp.Kvs[0].Value))

Get 方法的返回值如下：

其中 Header *ResponseHeader 几乎是etcd所有方法返回值中都会包含的，它包含了集群ID、etcd节点成员ID、key全局版本号、raft任期号：

Kvs []*mvccpb.KeyValue 包含多个键值对的信息，几乎etcd所有方法返回的键值对信息都由 mvccpb.KeyValue 表示，其结构如下：

 

5. Get values according to key prefix

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ctx, cancel := context.WithTimeout(context.Background(), time.Duration(opTimeout)*time.Second) defer cancel()   prefix := "name" resp, err := cli.Get(ctx, prefix, clientv3.WithPrefix()) if err != nil {     fmt.Printf("Get key prefix[%s] failed: %v\n", prefix, err)     return } if len(resp.Kvs) == 0 {     fmt.Printf("Key prefix[%s] not exists.\n", prefix)     return }   fmt.Println("values: ", resp.Kvs)

 

6. put

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ctx, cancel := context.WithTimeout(context.Background(), time.Duration(opTimeout)*time.Second) defer cancel()   key := "name" value := "shiajun" _, err = cli.Put(ctx, key, value) if err != nil {     fmt.Printf("Put key[%s] value[%s] failed: %v\n", key, value, err)     return } fmt.Println("put success")

Put 方法返回值如下：

prevKv 表示当前Put操作执行之前该key的键值对信息，Put方法第四个参数加上 clientv3.WithPrevKV() 即可返回该信息，如下一个例子所示。

 

7. put new value and get prev value

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ctx, cancel := context.WithTimeout(context.Background(), time.Duration(opTimeout)*time.Second) defer cancel()   key := "name" value := "shiajun" opts := []clientv3.OpOption{clientv3.WithPrevKV()} resp, err := cli.Put(ctx, key, value, opts...) if err != nil {     fmt.Printf("Put key[%s] value[%s] failed: %v\n", key, value, err)     return } fmt.Println("prev value: ", string(resp.PrevKv.Value))

 

8. put with lease

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ctx, cancel := context.WithTimeout(context.Background(), time.Duration(opTimeout)*time.Second) defer cancel()   //grant lease var ttl int64 = 10 lease, err := cli.Grant(ctx, ttl) if err != nil {     fmt.Printf("Grant lease failed: %v\n", err) }   //put with lease key := "name" value := "shiajun" _, err = cli.Put(ctx, key, value, clientv3.WithLease(lease.ID)) if err != nil {     fmt.Printf("Put key[%s] value[%s] with lease[%s] failed: %v\n", key, value, lease.ID, err) }   fmt.Println("put with lease success")

Grant 方法返回值如下：

 

 

9. put with lease and keep alive

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ctx, cancel := context.WithTimeout(context.Background(), time.Duration(opTimeout)*time.Second) defer cancel()   //grant lease var ttl int64 = 10 lease, err := cli.Grant(ctx, ttl) if err != nil {     fmt.Printf("Grant lease failed: %v\n", err) }   //put with lease key := "name" value := "shiajun" _, err = cli.Put(ctx, key, value, clientv3.WithLease(lease.ID)) if err != nil {     fmt.Printf("Put key[%s] value[%s] with lease[%s] failed: %v\n", key, value, lease.ID, err) }   //keep alive kaCh, err := cli.KeepAlive(context.Background(), lease.ID) if err != nil {     fmt.Printf("Keep alive key[%s] value[%s] with lease[%s] failed: %v\n", key, value, lease.ID, err) } for {     kaResp := <-kaCh     fmt.Println("ttl: ", kaResp.TTL) }

KeepAlive 方法返回值为一个channel：<-chan *LeaseKeepAliveResponse，接收每一次 keep alive 的结果返回：

 

10. delete

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ctx, cancel := context.WithTimeout(context.Background(), time.Duration(opTimeout)*time.Second) defer cancel()   key := "name" _, err = cli.Delete(ctx, key) if err != nil {     fmt.Printf("Delete key[%s] failed: %v\n", key, err)     return } fmt.Println("delete success")

Delete 方法返回值如下：

 

11. watch

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key := "name" opts := []clientv3.OpOption{clientv3.WithPrevKV(), clientv3.WithPrefix()} wCh := cli.Watch(context.Background(), key, opts...) for resp := range wCh {     for _, event := range resp.Events {         if event.Type == mvccpb.PUT {             fmt.Println("put happens")         } else if event.Type == mvccpb.DELETE {             fmt.Println("delete happens")         }         fmt.Println("prev value: ", event.PrevKv)         fmt.Println("value: ", event.Kv)     } }

Watch 方法返回值为一个Channel：<-chan WatchResponse，接收watch的结果信息：

对watch的key进行put、delete操作，watch操作即可获得变更结果，示例如下：

 

12. compare and set - transation

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ctx, cancel := context.WithTimeout(context.Background(), time.Duration(opTimeout)*time.Second) defer cancel()   key := "number" kvc := clientv3.NewKV(cli) resp, err := kvc.Txn(ctx).     If(clientv3.Compare(clientv3.Value(key), ">", "0")).     Then(clientv3.OpPut(key, "100")).     Else(clientv3.OpPut(key, "99")).     Commit() if err != nil {     fmt.Errorf("Compare and set transation failed: %v\n", err) }   fmt.Println(resp.Succeeded)

这是使用etcd事务实现的一个先比较再赋值的简单例子：若 number 的值大于0，则将number赋值为100，否则赋值为99。