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在集群中，有些业务逻辑只需要1个实例去执行，例如定时通知、任务调度器等。本文通过redis实现了在集群中选举一个master实例。

package redisutilimport ("context""errors""fmt""time""github.com/google/uuid""github.com/go-redis/redis/v9"
)const expiration = 20 * time.Secondvar instanceID = func() string {ips := util.HostIPsif len(ips) == 0 {ips = []string{"unknown_ip"}}return fmt.Sprintf("%s:%s", ips[0], uuid.New().String())
}()// AcquireAsMaster 选举master。如果当前节点选中为master，则向后执行；如果没选中，则阻塞等待下一次选举
func AcquireAsMaster(ctx context.Context, client redis.Client, lockName string) (instance string, release func() error, err error) {for wait := 5; ; wait = (wait << 1) % 75 { // 5, 10, 20, 40, 5, 10, ...select {case <-ctx.Done():return instanceID, func() error { return nil }, ctx.Err()default:}masterKey := fmt.Sprintf("%s:%s:master", strgen.ClusterTopic(), lockName)beElected, err := client.SetNX(ctx, masterKey, instanceID, expiration).Result()if err != nil || !beElected {time.Sleep(time.Duration(wait) * time.Second) // 选举出错了 or 选举落选，指数退避重新选举}if beElected {// 启动看门狗无限续期，防止master身份丢失go watchDog(ctx, client, masterKey)// 返回释放函数releaseFunc := func() error {released, e := client.Do(context.Background(), "EVAL", `if redis.call("GET", KEYS[1]) == ARGV[1] thenreturn redis.call("DEL", KEYS[1])endreturn 0`, 1, masterKey, instanceID).Result()if e != nil {return fmt.Errorf("failed to release as master: %w", e)}if released == 0 {return errors.New("failed to release as master: not master")}return nil}return instanceID, releaseFunc, nil}}
}// 看门狗无限需求，直到ctx结束
func watchDog(ctx context.Context, c redis.Client, masterK string) {ticker := time.NewTicker(expiration / 3)defer ticker.Stop()for {select {case <-ctx.Done():returncase <-ticker.C:success, er := c.Do(ctx, "EVAL", `if redis.call("GET", KEYS[1]) == ARGV[1] thenreturn redis.call("EXPIRE", KEYS[1], ARGV[2])endreturn 0`, 1, masterK, instanceID, int(expiration.Seconds())).Result()if er != nil || success == 0 {return}}}
}

使用示例：

instanceID, release, err := redisutil.AcquireAsMaster(ctx, myClient, "test-worker")
defer release()
if err != nil {xlog.Error(ctx, "failed to be master: %+v", err)return
}
xlog.Info(ctx, "%s becomes master.", instanceID)