通过redis选主进程

本文介绍了一种基于Redis的快速实现主进程选举方案。通过生成唯一标识符并利用Redis的SETNX指令来确保集群中只有一个主进程。该方案适用于需要在多个进程中选出一个主进程的场景。

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选主进程的方式有很多,完善点的方案就是zookeeper来做。这里介绍的是一种基于redis选主的方案,快速开发,快速实现。

Springside4里有个MasterElector类,细读代码后整理出自己的总结如下。

1.      业务进程启动时生成hostId,hostId的规则是“主机名-随机数”,一台主机部署多个进程实例的情况,也可以改为“主机名-端口”。

2.      业务进程调用jedis.get(masterKey)获取masterFromRedis。

3.      如果masterFromRedis为空,调用setnx(masterKey, hostId)方法设值,方法返回值大于0当前进程选为主进程,并且expire(masterKey,expireSeconds)设置key的有效期。Setnx返回值小于等于0时不能选为主进程。

如果masterFromRedis等于hostId,当前进程选为主进程,并且expire(masterKey, expireSeconds)设置key的有效期。

4.      按时间间隔intervalSeconds定期执行第二步和第三步。

 

 

当get(masterKey)之后获取到的masterFromRdis为空,在setnx之前,有其他进程已经Set了masterKey的值,本进程再调用setnx返回0失败.reids api文档有详细介绍:

 

SETNX key value

将 key 的值设为 value ,当且仅当 key 不存在。

若给定的 key 已经存在,则 SETNX 不做任何动作。

SETNX 是『SET if Not eXists』(如果不存在,则 SET)的简写。

可用版本:

>= 1.0.0

时间复杂度:

O(1)

返回值:

设置成功,返回 1 。

设置失败,返回 0 。

 

intervalSeconds定时时间间隔设置短些,可以减少异常情况下没有主的情况。

附上springside4的代码

 

 

public class MasterElector implementsRunnable {

 

                   publicstatic final String DEFAULT_MASTER_KEY = "master";

 

                   privatestatic Logger logger = LoggerFactory.getLogger(MasterElector.class);

 

                   privatestatic AtomicInteger poolNumber = new AtomicInteger(1);

                   privateScheduledExecutorService internalScheduledThreadPool;

                   privateScheduledFuture electorJob;

                   privateint intervalSeconds;

 

                   privateJedisTemplate jedisTemplate;

 

                   privateint expireSeconds;

                   privateString hostId;

                   privateAtomicBoolean master = new AtomicBoolean(false);

                   privateString masterKey = DEFAULT_MASTER_KEY;

 

                   publicMasterElector(JedisPool jedisPool, int intervalSeconds, int expireSeconds) {

                                      jedisTemplate= new JedisTemplate(jedisPool);

                                      this.expireSeconds= expireSeconds;

                                      this.intervalSeconds= intervalSeconds;

                   }

 

                   /**

                    * 发挥目前该实例是否master

                    */

                   publicboolean isMaster() {

                                      returnmaster.get();

                   }

 

                   /**

                    * 启动抢注线程, 自行创建scheduler线程池.

                    */

                   publicvoid start() {

                                      internalScheduledThreadPool= Executors.newScheduledThreadPool(1,

                                                                            Threads.buildJobFactory("Master-Elector-"+ poolNumber.getAndIncrement() + "-%d"));

                                      start(internalScheduledThreadPool);

                   }

 

                   /**

                    * 启动抢注线程, 使用传入的scheduler线程池.

                    */

                   publicvoid start(ScheduledExecutorService scheduledThreadPool) {

                                      if(intervalSeconds >= expireSeconds) {

                                                         thrownew IllegalArgumentException("periodSeconds must less than expireSeconds.periodSeconds is "

                                                                                               +intervalSeconds + " expireSeconds is " + expireSeconds);

                                      }

 

                                      hostId= generateHostId();

                                      electorJob= scheduledThreadPool.scheduleAtFixedRate(new WrapExceptionRunnable(this), 0,intervalSeconds,

                                                                            TimeUnit.SECONDS);

                                      logger.info("masterElectorstart, hostName:{}.", hostId);

                   }

 

                   /**

                    * 停止分发任务,如果是自行创建的threadPool则自行销毁。

                    */

                   publicvoid stop() {

                                      electorJob.cancel(false);

 

                                      if(internalScheduledThreadPool != null) {

                                                         Threads.normalShutdown(internalScheduledThreadPool,5, TimeUnit.SECONDS);

                                      }

                   }

 

                   /**

                    * 生成host id的方法哦,可在子类重载.

                    */

                   protectedString generateHostId() {

                                      Stringhost = "localhost";

                                      try{

                                                         host= InetAddress.getLocalHost().getHostName();

                                      }catch (UnknownHostException e) {

                                                         logger.warn("cannot get hostName", e);

                                      }

                                      host= host + "-" + new SecureRandom().nextInt(10000);

 

                                      returnhost;

                   }

 

                   @Override

                   publicvoid run() {

                                      jedisTemplate.execute(newJedisActionNoResult() {// NOSONAR

                                                                                               @Override

                                                                                               publicvoid action(Jedis jedis) {

                                                                                                                  StringmasterFromRedis = jedis.get(masterKey);

 

                                                                                                                  logger.debug("masteris {}", masterFromRedis);

 

                                                                                                                  //if master is null, the cluster just start or the master had crashed, try toregister myself

                                                                                                                  //as master

                                                                                                                  if(masterFromRedis == null) {

                                                                                                                                     //use setnx to make sure only one client can register as master.

                                                                                                                                     if(jedis.setnx(masterKey, hostId) > 0) {

                                                                                                                                                        jedis.expire(masterKey,expireSeconds);

                                                                                                                                                        master.set(true);

 

                                                                                                                                                        logger.info("masteris changed to {}.", hostId);

                                                                                                                                                        return;

                                                                                                                                     }else {

                                                                                                                                                        master.set(false);

                                                                                                                                                        return;

                                                                                                                                     }

                                                                                                                  }

 

                                                                                                                  //if master is myself, update the expire time.

                                                                                                                  if(hostId.equals(masterFromRedis)) {

                                                                                                                                     jedis.expire(masterKey,expireSeconds);

                                                                                                                                     master.set(true);

                                                                                                                                     return;

                                                                                                                  }

 

                                                                                                                  master.set(false);

                                                                                               }

                                                                            });

                   }

 

                   /**

                    * 如果应用中有多种master,设置唯一的mastername

                    */

                   publicvoid setMasterKey(String masterKey) {

                                      this.masterKey= masterKey;

                   }

 

                   //for test

                   publicvoid setHostId(String hostId) {

                                      this.hostId= hostId;

                   }

}

 

### 配置和实现 Redis三从集群的备自动切换 #### 备切换机制概述 Redis Cluster 是一种分布式解决方案,在面对单点故障时能够提供高可用性和数据冗余。当一个节点发生故障时,其对应的从节点会通过举过程晋升为节点,从而保证系统的持续运行和服务不中断[^2]。 #### 安装与基本设置 为了构建一个稳定的三三从架构,首先需要完成基础环境准备: 1. 下载并安装最新版本的 Redis 软件包。 2. 创建六个实例分别作为三个服务器及其相应的备份副本。 #### 开启持久化功能 编辑每个节点的 `redis.conf` 文件以启用 AOF 或 RDB 持久化项,这有助于防止因意外断电等原因造成的数据丢失问题。 ```bash appendonly yes ``` #### 设置密码保护(可) 如果希望增加安全性,则可以在所有配置文件中加入如下指令来设定访问控制列表 (ACL),并通过命令行参数传递给守护进程: ```bash requirepass your_password_here masterauth same_as_above ``` #### 启动多个 Redis 实例 对于每一个独立的服务端口都需要单独创建一份配置文档,并调整监听地址以及端口号等相关属性;之后利用 Docker 命令或者其他方式启动这些服务实例[^4]: ```dockerfile docker run -p external_port:internal_redis_port \ --name unique_container_name \ -v host_config_path:/etc/redis/redis.conf \ -v host_data_directory:/data \ -d redis_image_tag \ redis-server /etc/redis/redis.conf ``` #### 自定义哨兵监控程序 编写一组 Sentinel 进程用于监测整个网络内的健康状况,一旦检测到某个 master 出现异常即刻触发 failover 流程将 slave 提升为新的 leader[^3]. ```ini sentinel monitor mycluster ip_address_of_master port quorum_value sentinel down-after-milliseconds mycluster timeout_duration sentinel parallel-syncs mycluster max_sync_count sentinel failover-timeout mycluster time_limit_for_failover_operations ``` #### 确认集群状态正常工作 最后一步是验证各个组件之间的通信是否顺畅无阻塞现象存在,可以通过 CLI 工具发送 INFO 请求查看当前拓扑结构图样。 ---
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