Spring Boot（十三）：整合Redis哨兵，集群模式实践

前面的两篇文章（Redis的持久化方案，一文掌握Redis的三种集群方案）分别介绍了Redis的持久化与集群方案 —— 包括主从复制模式、哨兵模式、Cluster模式，其中主从复制模式由于不能自动做故障转移，当节点出现故障时需要人为干预，不满足生产环境的高可用需求，所以在生产环境一般使用哨兵模式或Cluster模式。那么在Spring Boot项目中，如何访问这两种模式的Redis集群，可能遇到哪些问题，是本文即将介绍的内容。

Spring Boot 2 整合Redis

spring boot中整合Redis非常简单，在pom.xml中添加依赖

<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>

spring boot 2的spring-boot-starter-data-redis中，默认使用的是lettuce作为redis客户端，它与jedis的主要区别如下：

Jedis是同步的，不支持异步，Jedis客户端实例不是线程安全的，需要每个线程一个Jedis实例，所以一般通过连接池来使用Jedis
Lettuce是基于Netty框架的事件驱动的Redis客户端，其方法调用是异步的，Lettuce的API也是线程安全的，所以多个线程可以操作单个Lettuce连接来完成各种操作，同时Lettuce也支持连接池

如果不使用默认的lettuce，使用jedis的话，可以排除lettuce的依赖，手动加入jedis依赖，配置如下

<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-redis</artifactId><exclusions><exclusion><groupId>io.lettuce</groupId><artifactId>lettuce-core</artifactId></exclusion></exclusions>
</dependency>
<dependency><groupId>redis.clients</groupId><artifactId>jedis</artifactId><version>2.9.0</version>
</dependency>

在配置文件application.yml中添加配置（针对单实例）

spring:redis:host: 192.168.40.201port: 6379password: passw0rddatabase: 0 # 数据库索引，默认0timeout: 5000  # 连接超时，单位msjedis:  # 或lettuce, 连接池配置，springboot2.0中使用jedis或者lettuce配置连接池，默认为lettuce连接池pool:max-active: 8 # 连接池最大连接数（使用负值表示没有限制）max-wait: -1 # 连接池分配连接最大阻塞等待时间（阻塞时间到，抛出异常。使用负值表示无限期阻塞）max-idle: 8 # 连接池中的最大空闲连接数min-idle: 0 # 连接池中的最小空闲连接数

然后添加配置类。其中@EnableCaching注解是为了使@Cacheable、@CacheEvict、@CachePut、@Caching注解生效

@Configuration
@EnableCaching
public class RedisConfig {@Beanpublic RedisTemplate<String, Object> redisTemplate(RedisConnectionFactory factory) {RedisTemplate<String, Object> template = new RedisTemplate<>();template.setConnectionFactory(factory);// 使用Jackson2JsonRedisSerialize 替换默认的jdkSerializeable序列化Jackson2JsonRedisSerializer jackson2JsonRedisSerializer = new Jackson2JsonRedisSerializer(Object.class);ObjectMapper om = new ObjectMapper();om.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.ANY);om.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL);jackson2JsonRedisSerializer.setObjectMapper(om);StringRedisSerializer stringRedisSerializer = new StringRedisSerializer();// key采用String的序列化方式template.setKeySerializer(stringRedisSerializer);// hash的key也采用String的序列化方式template.setHashKeySerializer(stringRedisSerializer);// value序列化方式采用jacksontemplate.setValueSerializer(jackson2JsonRedisSerializer);// hash的value序列化方式采用jacksontemplate.setHashValueSerializer(jackson2JsonRedisSerializer);template.afterPropertiesSet();return template;}
}

上述配置类注入了自定义的RedisTemplate<String, Object>，替换RedisAutoConfiguration中自动配置的RedisTemplate<Object, Object>类（RedisAutoConfiguration另外还自动配置了StringRedisTemplate）。

此时，我们可以通过定义一个基于RedisTemplate的工具类，或通过在Service层添加@Cacheable、@CacheEvict、@CachePut、@Caching注解来使用缓存。比如定义一个RedisService类，封装常用的Redis操作方法，

@Component
@Slf4j
public class RedisService {@Autowiredprivate RedisTemplate<String, Object> redisTemplate;/*** 指定缓存失效时间** @param key 键* @param time 时间(秒)* @return*/public boolean expire(String key, long time) {try {if (time > 0) {redisTemplate.expire(key, time, TimeUnit.SECONDS);}return true;} catch (Exception e) {log.error("exception when expire key {}. ", key, e);return false;}}/*** 根据key获取过期时间** @param key 键 不能为null* @return 时间(秒) 返回0代表为永久有效*/public long getExpire(String key) {return redisTemplate.getExpire(key, TimeUnit.SECONDS);}/*** 判断key是否存在** @param key  键* @return true 存在 false不存在*/public boolean hasKey(String key) {try {return redisTemplate.hasKey(key);} catch (Exception e) {log.error("exception when check key {}. ", key, e);return false;}}...
}

出于篇幅，完整代码请查阅本文示例源码： https://github.com/ronwxy/springboot-demos/tree/master/springboot-redis-sentinel

或在Service层使用注解，如

@Service
@CacheConfig(cacheNames = "users")
public class UserService {private static Map<String, User> userMap = new HashMap<>();@CachePut(key = "#user.username")public User addUser(User user){user.setUid(UUID.randomUUID().toString());System.out.println("add user: " + user);userMap.put(user.getUsername(), user);return user;}@Caching(put = {@CachePut( key = "#user.username"),@CachePut( key = "#user.uid")})public User addUser2(User user) {user.setUid(UUID.randomUUID().toString());System.out.println("add user2: " + user);userMap.put(user.getUsername(), user);return user;}...
}

Spring Boot 2 整合Redis哨兵模式

Spring Boot 2 整合Redis哨兵模式除了配置稍有差异，其它与整合单实例模式类似，配置示例为

spring:redis:password: passw0rdtimeout: 5000sentinel:master: mymasternodes: 192.168.40.201:26379,192.168.40.201:36379,192.168.40.201:46379 # 哨兵的IP:Port列表jedis: # 或lettucepool:max-active: 8max-wait: -1max-idle: 8min-idle: 0

完整示例可查阅源码： https://github.com/ronwxy/springboot-demos/tree/master/springboot-redis-sentinel

上述配置只指定了哨兵节点的地址与master的名称，但Redis客户端最终访问操作的是master节点，那么Redis客户端是如何获取master节点的地址，并在发生故障转移时，如何自动切换master地址的呢？我们以Jedis连接池为例，通过源码来揭开其内部实现的神秘面纱。

在 JedisSentinelPool 类的构造函数中，对连接池做了初始化，如下

 public JedisSentinelPool(String masterName, Set<String> sentinels,final GenericObjectPoolConfig poolConfig, final int connectionTimeout, final int soTimeout,final String password, final int database, final String clientName) {this.poolConfig = poolConfig;this.connectionTimeout = connectionTimeout;this.soTimeout = soTimeout;this.password = password;this.database = database;this.clientName = clientName;HostAndPort master = initSentinels(sentinels, masterName);initPool(master);}private HostAndPort initSentinels(Set<String> sentinels, final String masterName) {for (String sentinel : sentinels) {final HostAndPort hap = HostAndPort.parseString(sentinel);log.fine("Connecting to Sentinel " + hap);Jedis jedis = null;try {jedis = new Jedis(hap.getHost(), hap.getPort());List<String> masterAddr = jedis.sentinelGetMasterAddrByName(masterName);// connected to sentinel...sentinelAvailable = true;if (masterAddr == null || masterAddr.size() != 2) {log.warning("Can not get master addr, master name: " + masterName + ". Sentinel: " + hap+ ".");continue;}master = toHostAndPort(masterAddr);log.fine("Found Redis master at " + master);break;} catch (JedisException e) {// resolves #1036, it should handle JedisException there's another chance// of raising JedisDataExceptionlog.warning("Cannot get master address from sentinel running @ " + hap + ". Reason: " + e+ ". Trying next one.");} finally {if (jedis != null) {jedis.close();}}}//省略了非关键代码for (String sentinel : sentinels) {final HostAndPort hap = HostAndPort.parseString(sentinel);MasterListener masterListener = new MasterListener(masterName, hap.getHost(), hap.getPort());// whether MasterListener threads are alive or not, process can be stoppedmasterListener.setDaemon(true);masterListeners.add(masterListener);masterListener.start();}return master;}

initSentinels 方法中主要干了两件事：

遍历哨兵节点，通过get-master-addr-by-name命令获取master节点的地址信息，找到了就退出循环。get-master-addr-by-name命令执行结果如下所示

[root@dev-server-1 master-slave]# redis-cli -p 26379
127.0.0.1:26379> sentinel get-master-addr-by-name mymaster
1) "192.168.40.201"
2) "7001"
127.0.0.1:26379>

对每一个哨兵节点通过一个 MasterListener 进行监听（Redis的发布订阅功能），订阅哨兵节点+switch-master频道，当发生故障转移时，客户端能收到哨兵的通知，通过重新初始化连接池，完成主节点的切换。 MasterListener.run方法中监听哨兵部分代码如下

 j.subscribe(new JedisPubSub() {@Overridepublic void onMessage(String channel, String message) {log.fine("Sentinel " + host + ":" + port + " published: " + message + ".");String[] switchMasterMsg = message.split(" ");if (switchMasterMsg.length > 3) {if (masterName.equals(switchMasterMsg[0])) {initPool(toHostAndPort(Arrays.asList(switchMasterMsg[3], switchMasterMsg[4])));} else {log.fine("Ignoring message on +switch-master for master name "+ switchMasterMsg[0] + ", our master name is " + masterName);}} else {log.severe("Invalid message received on Sentinel " + host + ":" + port+ " on channel +switch-master: " + message);}}}, "+switch-master");

initPool 方法如下：如果发现新的master节点与当前的master不同，则重新初始化。

private void initPool(HostAndPort master) {if (!master.equals(currentHostMaster)) {currentHostMaster = master;if (factory == null) {factory = new JedisFactory(master.getHost(), master.getPort(), connectionTimeout,soTimeout, password, database, clientName, false, null, null, null);initPool(poolConfig, factory);} else {factory.setHostAndPort(currentHostMaster);// although we clear the pool, we still have to check the// returned object// in getResource, this call only clears idle instances, not// borrowed instancesinternalPool.clear();}log.info("Created JedisPool to master at " + master);}}

通过以上两步，Jedis客户端在只知道哨兵地址的情况下便能获得master节点的地址信息，并且当发生故障转移时能自动切换到新的master节点地址。

Spring Boot 2 整合Redis Cluster模式

Spring Boot 2 整合Redis Cluster模式除了配置稍有差异，其它与整合单实例模式也类似，配置示例为

spring:redis:password: passw0rdtimeout: 5000database: 0cluster:nodes: 192.168.40.201:7100,192.168.40.201:7200,192.168.40.201:7300,192.168.40.201:7400,192.168.40.201:7500,192.168.40.201:7600max-redirects: 3  # 重定向的最大次数jedis:pool:max-active: 8max-wait: -1max-idle: 8min-idle: 0

完整示例可查阅源码： https://github.com/ronwxy/springboot-demos/tree/master/springboot-redis-cluster

在一文掌握Redis的三种集群方案中已经介绍了Cluster模式访问的基本原理，可以通过任意节点跳转到目标节点执行命令，上面配置中 max-redirects 控制在集群中跳转的最大次数。

查看JedisClusterConnection的execute方法，

public Object execute(String command, byte[]... args) {Assert.notNull(command, "Command must not be null!");Assert.notNull(args, "Args must not be null!");return clusterCommandExecutor.executeCommandOnArbitraryNode((JedisClusterCommandCallback<Object>) client -> JedisClientUtils.execute(command,EMPTY_2D_BYTE_ARRAY, args, () -> client)).getValue();
}

集群命令的执行是通过ClusterCommandExecutor.executeCommandOnArbitraryNode来实现的，

public <T> NodeResult<T> executeCommandOnArbitraryNode(ClusterCommandCallback<?, T> cmd) {Assert.notNull(cmd, "ClusterCommandCallback must not be null!");List<RedisClusterNode> nodes = new ArrayList<>(getClusterTopology().getActiveNodes());return executeCommandOnSingleNode(cmd, nodes.get(new Random().nextInt(nodes.size())));
}private <S, T> NodeResult<T> executeCommandOnSingleNode(ClusterCommandCallback<S, T> cmd, RedisClusterNode node,int redirectCount) {Assert.notNull(cmd, "ClusterCommandCallback must not be null!");Assert.notNull(node, "RedisClusterNode must not be null!");if (redirectCount > maxRedirects) {throw new TooManyClusterRedirectionsException(String.format("Cannot follow Cluster Redirects over more than %s legs. Please consider increasing the number of redirects to follow. Current value is: %s.",redirectCount, maxRedirects));}RedisClusterNode nodeToUse = lookupNode(node);S client = this.resourceProvider.getResourceForSpecificNode(nodeToUse);Assert.notNull(client, "Could not acquire resource for node. Is your cluster info up to date?");try {return new NodeResult<>(node, cmd.doInCluster(client));} catch (RuntimeException ex) {RuntimeException translatedException = convertToDataAccessException(ex);if (translatedException instanceof ClusterRedirectException) {ClusterRedirectException cre = (ClusterRedirectException) translatedException;return executeCommandOnSingleNode(cmd,topologyProvider.getTopology().lookup(cre.getTargetHost(), cre.getTargetPort()), redirectCount + 1);} else {throw translatedException != null ? translatedException : ex;}} finally {this.resourceProvider.returnResourceForSpecificNode(nodeToUse, client);}
}

上述代码逻辑如下

从集群节点列表中随机选择一个节点
从该节点获取一个客户端连接（如果配置了连接池，从连接池中获取），执行命令
如果抛出ClusterRedirectException异常，则跳转到返回的目标节点上执行
如果跳转次数大于配置的值 max-redirects，则抛出TooManyClusterRedirectionsException异常

可能遇到的问题

Redis连接超时

检查服务是否正常启动（比如 ps -ef|grep redis查看进程，netstat -ano|grep 6379查看端口是否起来，以及日志文件），如果正常启动，则查看Redis服务器是否开启防火墙，关闭防火墙或配置通行端口。

Cluster模式下，报连接到127.0.0.1被拒绝错误，如 Connection refused: no further information: /127.0.0.1:7600

这是因为在redis.conf中配置 bind 0.0.0.0 或 bind 127.0.0.1导致，需要改为具体在外部可访问的IP，如 bind 192.168.40.201。如果之前已经起了集群，并产生了数据，则修改redis.conf文件后，还需要修改cluster-config-file文件，将127.0.0.1替换为bind 的具体IP，然后重启。

master挂了，slave升级成为master，重启master，不能正常同步新的master数据

如果设置了密码，需要在master, slave的配置文件中都配置masterauth password