etcd租约机制及自动过期的实例分析

这篇文章给大家介绍etcd租约机制及自动过期的实例分析，内容非常详细，感兴趣的小伙伴们可以参考借鉴，希望对大家能有所帮助。

对于实现分布式乐观锁非常重要。如果锁了，突然宕机了，锁是需要自动释放的。所以这锁在etcd里是需要生命期的。
过期演示：

package mainimport (    "context"    "fmt"    "go.etcd.io/etcd/clientv3"    "time")func main() {    var (        config  clientv3.Config        client  *clientv3.Client        err     error        lease clientv3.Lease        leaseGrantResp *clientv3.LeaseGrantResponse        leaseId clientv3.LeaseID        putResp *clientv3.PutResponse        kv clientv3.KV        getResp *clientv3.GetResponse    )    //客户端配置    config = clientv3.Config{        Endpoints:   []string{"0.0.0.0:2379"}, //集群列表        DialTimeout: 5 * time.Second,    }    //建立客户端    if client, err = clientv3.New(config); err != nil {        fmt.Println(err)        return    }    //申请一个lease(租约)    lease = clientv3.NewLease(client)    //申请一个5秒的租约    if leaseGrantResp, err = lease.Grant(context.TODO(), 5); err != nil {        fmt.Println(err)        return    }    //拿到租约的id    leaseId = leaseGrantResp.ID    //获得kv api子集    kv = clientv3.NewKV(client)    //put一个kv，让它与租约关联起来，从而实现10秒后自动过期    if putResp, err = kv.Put(context.TODO(), "/cron/lock/job1", "", clientv3.WithLease(leaseId)); err != nil {        fmt.Println(err)        return    }    fmt.Println("写入成功:", putResp.Header.Revision)    //定时看key过期没    for {        if getResp, err = kv.Get(context.TODO(), "/cron/lock/job1"); err != nil {            fmt.Println(err)            return        }        if getResp.Count == 0 {            fmt.Println("kv过期了")            break        }        fmt.Println("还没过期:", getResp.Kvs)        time.Sleep(time.Second)    }}

[root@bogon etcd]# go run demo6.go
写入成功: 27
还没过期: [key:"/cron/lock/job1" create_revision:27 mod_revision:27 version:1 lease:7587837741646622005 ]
还没过期: [key:"/cron/lock/job1" create_revision:27 mod_revision:27 version:1 lease:7587837741646622005 ]
还没过期: [key:"/cron/lock/job1" create_revision:27 mod_revision:27 version:1 lease:7587837741646622005 ]
还没过期: [key:"/cron/lock/job1" create_revision:27 mod_revision:27 version:1 lease:7587837741646622005 ]
还没过期: [key:"/cron/lock/job1" create_revision:27 mod_revision:27 version:1 lease:7587837741646622005 ]
还没过期: [key:"/cron/lock/job1" create_revision:27 mod_revision:27 version:1 lease:7587837741646622005 ]
kv过期了
[root@bogon etcd]#

申请一把分布式锁的时候，是谁抢到了key就是抢到了锁，如果不主动释放这锁，按道理讲不应该让租约过期，租约过期主要是为了程序宕掉之后，锁自动释放，防止程序异常退出。如果程序抢到了这个锁，我们希望锁一直不失效，知道我们主动释放它：

package mainimport (    "context"    "fmt"    "go.etcd.io/etcd/clientv3"    "time")func main() {    var (        config  clientv3.Config        client  *clientv3.Client        err     error        lease clientv3.Lease        leaseGrantResp *clientv3.LeaseGrantResponse        leaseId clientv3.LeaseID        putResp *clientv3.PutResponse        kv clientv3.KV        getResp *clientv3.GetResponse        keepResp *clientv3.LeaseKeepAliveResponse        keepRespChan <-chan *clientv3.LeaseKeepAliveResponse //只读channel    )    //客户端配置    config = clientv3.Config{        Endpoints:   []string{"0.0.0.0:2379"}, //集群列表        DialTimeout: 5 * time.Second,    }    //建立客户端    if client, err = clientv3.New(config); err != nil {        fmt.Println(err)        return    }    //申请一个lease(租约)    lease = clientv3.NewLease(client)    //申请一个5秒的租约    if leaseGrantResp, err = lease.Grant(context.TODO(), 5); err != nil {        fmt.Println(err)        return    }    //拿到租约的id    leaseId = leaseGrantResp.ID    //(自动续租)当我们申请了租约之后，我们就可以启动一个续租    if keepRespChan, err = lease.KeepAlive(context.TODO(), leaseId); err != nil {        fmt.Println(err)        return    }    //处理续租应答的协程    go func() {        for {            select {            case keepResp = <-keepRespChan:                if keepRespChan == nil {                    fmt.Println("租约已经失效")                    goto END                } else { //每秒会续租一次，所以就会受到一次应答                    fmt.Println("收到自动续租应答:", keepResp.ID)                }            }        }        END:    }()    //获得kv api子集    kv = clientv3.NewKV(client)    //put一个kv，让它与租约关联起来，从而实现10秒后自动过期    if putResp, err = kv.Put(context.TODO(), "/cron/lock/job1", "", clientv3.WithLease(leaseId)); err != nil {        fmt.Println(err)        return    }    fmt.Println("写入成功:", putResp.Header.Revision)    //定时看key过期没    for {        if getResp, err = kv.Get(context.TODO(), "/cron/lock/job1"); err != nil {            fmt.Println(err)            return        }        if getResp.Count == 0 {            fmt.Println("kv过期了")            break        }        fmt.Println("还没过期:", getResp.Kvs)        time.Sleep(time.Second)    }}

[root@bogon etcd]# go run demo7.go
写入成功: 30
收到自动续租应答: 7587837741646622039
还没过期: [key:"/cron/lock/job1" create_revision:29 mod_revision:30 version:2 lease:7587837741646622039 ]
还没过期: [key:"/cron/lock/job1" create_revision:29 mod_revision:30 version:2 lease:7587837741646622039 ]
收到自动续租应答: 7587837741646622039
还没过期: [key:"/cron/lock/job1" create_revision:29 mod_revision:30 version:2 lease:7587837741646622039 ]
还没过期: [key:"/cron/lock/job1" create_revision:29 mod_revision:30 version:2 lease:7587837741646622039 ]
还没过期: [key:"/cron/lock/job1" create_revision:29 mod_revision:30 version:2 lease:7587837741646622039 ]
收到自动续租应答: 7587837741646622039
还没过期: [key:"/cron/lock/job1" create_revision:29 mod_revision:30 version:2 lease:7587837741646622039 ]
还没过期: [key:"/cron/lock/job1" create_revision:29 mod_revision:30 version:2 lease:7587837741646622039 ]
收到自动续租应答: 7587837741646622039
......

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