etcd 使用： golang 例子

一：连接到 etcd

package main

import (
	"fmt"
	"go.etcd.io/etcd/clientv3"
	"time"
)

//连接
func main() {
	//客户端配置
	config := clientv3.Config{
		Endpoints:   []string{"192.168.1.109:2379"},
		DialTimeout: 5 * time.Second,
	}

	//建立连接
	if client, err := clientv3.New(config); err != nil {
		fmt.Println(err)
		return
	}
 
   fmt.Println("connect success")
	defer client.Close()
}

Endpoints：etcd的多个节点服务地址。
DialTimeout：创建client的首次连接超时时间，这里传了5秒，如果5秒都没有连接成功就会返回err；
一旦client创建成功，我们就不用再关心后续底层连接的状态了，client内部会重连。

二：KV操作：增 删 改 查

package main

import (
	"context"
	"fmt"
	"go.etcd.io/etcd/clientv3"
	"time"
)

func main() {
	client, err := clientv3.New(clientv3.Config{
		Endpoints:   []string{"192.168.1.109:2379", "192.168.1.109:2379"},
		DialTimeout: 5 * time.Second,
	})
	if err != nil {
		fmt.Println("connect failed, err :", err)
		return
	}

	defer client.Close()

	//控制超时
	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
   //1. 增-存值
	_, err = client.Put(ctx, "/demo/demo1_key", "demo1_value")
	//操作完毕，cancel掉
	cancel()
	if err != nil {
		fmt.Println("put failed, err:", err)
		return
	}

	//2. 查-获取值， 也设置超时
	ctx, cancel = context.WithTimeout(context.Background(), time.Second)
	resp, err := client.Get(ctx, "/demo/demo1_key")
   // Get查询还可以增加WithPrefix选项，获取某个目录下的所有子元素
   //eg: resp, err := client.Get(ctx, "/demo/", clientv3.WithPrefix())
	cancel()
	if err != nil {
		fmt.Println("get failed err:", err)
		return
	}

	for _, item := range resp.Kvs { //Kvs 返回key的列表
		fmt.Printf("%s : %s 
", item.Key, item.Value)
	}
 
   //3. 改-修改值
   ctx, _ = context.WithTimeout(context.Background(), time.Second)
   resp, err := client.Put(ctx, "/demo/demo1_key", "update_value", clientv3.WithPrevKV()))
   if err != nil {
       fmt.Println("get failed err: ", err)
   }
   fmt.Println(string(resp.PrevKv.Value))
   
   //4. 删-删除值
   ctx, _ = context.WithTimeout(context.Background(), time.Second)
   resp, err := client.Delete(ctx, "/demo/demo1_key")
   if err != nil {
       fmt.Println(err)
   }
   fmt.Println(resp.PrevKvs)
}

三：watch 监听

package main

import (
	"context"
	"fmt"
	"go.etcd.io/etcd/clientv3"
	"time"
)

func main() {
	client, err := clientv3.New(clientv3.Config{
		Endpoints:   []string{"192.168.1.109:2379"},
		DialTimeout: time.Second,
	})
	if err != nil {
		fmt.Println("connect failed err : ", err)
		return
	}
	defer client.Close()

	client.Put(context.Background(), "/demo/demo2_key", "demo2_value")
	go func() {
		//watch
		watchKey := client.Watch(context.Background(), "/demo/demo2_key")
		for resp := range watchKey {
			for _, item := range resp {
				fmt.Printf("%s %q : %q 
", item.Type, item.Kv.key, item.Kv.Value)
			}
		}
	}
    
    if resp, err := client.Put(context.TODO(), "/demo/demo2_key/", "demo2_watch"); err != nil {
        fmt.Println(err)
    } else {
        fmt.Println(resp)
    }
}

四：Transaction 事务

package main

import (
	"context"
	"fmt"
	"go.etcd.io/etcd/clientv3"
	"log"
	"sync"
	"time"
)

func main() {
	client, err := clientv3.New(clientv3.Config{
		Endpoints:   5 * time.Second,
		DialTimeout: 3 * time.Second,
	})
	if err != nil {
		fmt.Println("connect failed err: ", err)
		return
	}
	client.Close()

	var w sync.WaitGroup
	w.Add(10)
	key10 := "setnx"
	for i := 0; i < 10; i++ {
		go func(i int) {
			time.Sleep(5 * time.Millisecond)
			//通过key的Create_Revision 是否为 0 来判断key是否存在。其中If，Then 以及 Else 分支都可以包含多个操作。
			//返回的数据包含一个successed字段，当为 true 时代表 If 为真
			_, err := client.Txn(context.Background()).
				If(clientv3.Compare(clientv3.CreateRevision(key10), "=", 0)).
				Then(clientv3.OpPut(key10, fmt.Sprintf("%d", i))).
				Commit()
			if err != nil {
				fmt.Println(err)
			}

			w.Done()
		}(i)
	}
	w.Wait()

	if resp, err := client.Get(context.TODO(), key10); err != nil {
		log.Fatal(err)
	} else {
		log.Println(resp)
	}
}

五：lease 租约

package main

import (
	"time"
)
//From：https://github.com/the-gigi/go-etcd3-demo/blob/master/main.go
var (
	dialTimeout    = 2 * time.Second
	requestTimeout = 10 * time.Second
)

func main() {
	ctx, _ := context.WithTimeout(context.Background(), requestTimeout)
	client, err := clientv3.New(clientv3.Config{
		DialTimeout: dialTimeout,
		Endpoints:   []string{"localhost:2379"},
	})

	if err != nil {
		log.Fatal(err)
	}

	kv := clientv3.NewKv(client)

	//Delete all keys
	kv.Delete(ctx, "/demo/demo1_key", clientv3.WithPrefix())

	gr, _ := kv.Get(ctx, "/demo/demo1_key")
	if len(gr.Kvs) == 0 {
		fmt.Println("no key")
	}

	lease, err := client.Grant(ctx, 3)
	if err != nil {
		log.Fatal(err)
	}

	//Insert key with a lease of 3 second TTL
	kv.Put(ctx, "/demo/demo1_key", "demo1_value", clientv3.WithLease(lease.ID))

	gr, _ = kv.Get(ctx, "/demo/demo1_key")
	if len(gr.Kvs) == 1 {
		fmt.Println("Found key")
	}

	//let the TTL expire
	time.Sleep(3 * time.Second)

	gr, _ = kv.Get(ctx, "/demo/demo1_key")
	if len(gr.Kvs) == 0 {
		fmt.Println("no more key")
	}
}
//From：https://github.com/the-gigi/go-etcd3-demo/blob/master/main.go