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· 5 min read
sado

一、etcd​

1、简介​

etcd是使用Go语言开发的一个开源的、高可用的分布式key-value存储系统，可以用于配置共享和服务的注册和发现。

类似项目有`zookeeper`和`consul`。

2、特点​

`完全复制`：集群中的每个节点都可以使用完整的存档
`高可用性`：Etcd可用于避免硬件的单点故障或网络问题
`一致性`：每次读取都会返回跨多主机的最新写入
`简单`：包括一个定义良好、面向用户的API（gRPC）
`安全`：实现了带有可选的客户端证书身份验证的自动化TLS
`快速`：每秒10000次写入的基准速度
`可靠`：使用Raft算法实现了`强一致`、高可用的服务存储目录

3、应用场景​

服务发现
配置中心
分布式锁 - 1.保持独占 2.控制时序

注: 奇数节点原则

4、etcd集群​

...

5、go 操作 etcd​

go get go.etcd.io/etcd/clientv3

官方文档

PUT GET​
package main

import (
    "context"
    "fmt"
    "time"

    "go.etcd.io/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, "kk", "123")
    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, "kk")
    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​
package main

import (
    "context"
    "fmt"
    "time"

    "go.etcd.io/etcd/clientv3"
)

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:kk change
    rch := cli.Watch(context.Background(), "kk") // <-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)
        }
    }
}

命令行操作更改键值

etcd> etcdctl.exe --endpoints=http://127.0.0.1:2379 put kk "123"
OK

etcd> etcdctl.exe --endpoints=http://127.0.0.1:2379 del kk
1

etcd> etcdctl.exe --endpoints=http://127.0.0.1:2379 put kk "321"
OK

通知

watch> ./watch
connect to etcd success
Type: PUT Key:kk Value:123
Type: DELETE Key:kk Value:
Type: PUT Key:kk Value:321
LEASE​
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
    resp, err := cli.Grant(context.TODO(), 5)
    if err != nil {
        log.Fatal(err)
    }

    // 5秒钟之后, /nazha/ 这个key就会被移除
    _, err = cli.Put(context.TODO(), "/kk/", "123", clientv3.WithLease(resp.ID))
    if err != nil {
        log.Fatal(err)
    }
}

KEEPALIVE

package main

import (
    "context"
    "fmt"
    "log"
    "time"

    "go.etcd.io/etcd/clientv3"
)

// etcd keepAlive

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()

    resp, err := cli.Grant(context.TODO(), 5)
    if err != nil {
        log.Fatal(err)
    }

    _, err = cli.Put(context.TODO(), "/kk/", "123", clientv3.WithLease(resp.ID))
    if err != nil {
        log.Fatal(err)
    }

    // the key 'foo' will be kept forever
    ch, kaerr := cli.KeepAlive(context.TODO(), resp.ID)
    if kaerr != nil {
        log.Fatal(kaerr)
    }
    for {
        ka := <-ch
        fmt.Println("ttl:", ka.TTL)
    }
}

6、分布式锁​

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

acquired lock for s1
released lock for s1
acquired lock for s2