1. 操作ETCD

这里使用官方的包来连接etcd并进行相关操作。

1.1.2. put和get操作

put命令用来设置键值对数据，get命令用来根据key获取值。

package main
import (
    "context"
    "fmt"
    "time"
    "go.etcd.io/etcd/clientv3"
)
// etcd client put/get demo
// use etcd/clientv3
func main() {
    cli, err := clientv3.New(clientv3.Config{
        Endpoints:   []string{"127.0.0.1:2379"},
        DialTimeout: 5 * time.Second,
    })
    if err != nil {
        // handle error!
        fmt.Printf("connect to etcd failed, err:%v\n", err)
        return
    }
    fmt.Println("connect to etcd success")
    defer cli.Close()
    // put
    ctx, cancel := context.WithTimeout(context.Background(), time.Second)
    _, err = cli.Put(ctx, "lmh", "lmh")
    cancel()
    if err != nil {
        fmt.Printf("put to etcd failed, err:%v\n", err)
        return
    }
    // get
    ctx, cancel = context.WithTimeout(context.Background(), time.Second)
    resp, err := cli.Get(ctx, "lmh")
    cancel()
    if err != nil {
        fmt.Printf("get from etcd failed, err:%v\n", err)
        return
    }
    for _, ev := range resp.Kvs {
        fmt.Printf("%s:%s\n", ev.Key, ev.Value)
    }
}

watch用来获取未来更改的通知。

package main
import (
    "context"
    "fmt"
    "go.etcd.io/etcd/clientv3"
)
// watch demo
func main() {
    cli, err := clientv3.New(clientv3.Config{
        Endpoints:   []string{"127.0.0.1:2379"},
        DialTimeout: 5 * time.Second,
    })
    if err != nil {
        fmt.Printf("connect to etcd failed, err:%v\n", err)
        return
    }
    fmt.Println("connect to etcd success")
    defer cli.Close()
    // watch key:lmh change
    rch := cli.Watch(context.Background(), "lmh") // <-chan WatchResponse
    for wresp := range rch {
        for _, ev := range wresp.Events {
            fmt.Printf("Type: %s Key:%s Value:%s\n", ev.Type, ev.Kv.Key, ev.Kv.Value)
        }
    }
}

例如：我们打开终端执行以下命令修改、删除、设置lmh这个key。

上面的程序都能收到如下通知。

    watch>watch.exe
    connect to etcd success
    Type: PUT Key:lmh Value:lmh1
    Type: DELETE Key:lmh Value:
    Type: PUT Key:lmh Value:lmh2

1.1.4. lease租约

package main
import (
    "fmt"
    "time"
)
// etcd lease
import (
    "context"
    "log"
    "go.etcd.io/etcd/clientv3"
)
func main() {
    cli, err := clientv3.New(clientv3.Config{
        Endpoints:   []string{"127.0.0.1:2379"},
        DialTimeout: time.Second * 5,
    })
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println("connect to etcd success.")
    defer cli.Close()
    // 创建一个5秒的租约
    if err != nil {
        log.Fatal(err)
    }
    // 5秒钟之后, /lmh/ 这个key就会被移除
    _, err = cli.Put(context.TODO(), "/lmh/", "lmh", clientv3.WithLease(resp.ID))
    if err != nil {
        log.Fatal(err)
    }
}

1.1.6. 基于etcd实现分布式锁

go.etcd.io/etcd/clientv3/concurrency在etcd之上实现并发操作，如分布式锁、屏障和选举。

    import "go.etcd.io/etcd/clientv3/concurrency"

基于etcd实现的分布式锁示例：

cli, err := clientv3.New(clientv3.Config{Endpoints: endpoints})
if err != nil {
    log.Fatal(err)
}
defer cli.Close()
// 创建两个单独的会话用来演示锁竞争
s1, err := concurrency.NewSession(cli)
if err != nil {
    log.Fatal(err)
}
defer s1.Close()
m1 := concurrency.NewMutex(s1, "/my-lock/")
s2, err := concurrency.NewSession(cli)
if err != nil {
    log.Fatal(err)
}
defer s2.Close()
m2 := concurrency.NewMutex(s2, "/my-lock/")
// 会话s1获取锁
if err := m1.Lock(context.TODO()); err != nil {
    log.Fatal(err)
}
fmt.Println("acquired lock for s1")
m2Locked := make(chan struct{})
go func() {
    defer close(m2Locked)
    // 等待直到会话s1释放了/my-lock/的锁
    if err := m2.Lock(context.TODO()); err != nil {
        log.Fatal(err)
    }
}()
if err := m1.Unlock(context.TODO()); err != nil {
    log.Fatal(err)
}
fmt.Println("released lock for s1")
<-m2Locked
fmt.Println("acquired lock for s2")

输出：