Spring lettuce读写分离
Redis 的 Sentinel 模式默认配置下 Redis 的客户端只对 Master 读写，另外2个Slave闲置。若主从节点在不同机房，在读取时会有跨机房的网络时延，并且比同机房访问更容易发生网络丢包。故在一些场景可以考虑将跨机房的服务节点设置为读写分离
Redis 的 Sentinel 模式下最少是一主二从，不算 Sentinel 节点要占用3个节点
读写分离配置
{@link org.springframework.boot.autoconfigure.data.redis.LettuceConnectionConfiguration}
低版本为ReadFrom.SLAVE_PREFERRED，高版本为REPLICA_PREFERRED。作用为在从节点读取，若无可用从节点，则在主节点读取
LettuceClientConfiguration
@Configuration
public class LettuceClientConfiguration {@Value("${app.idc:}")private String idc;public static final String SHENZHEN = "shenzhen";@Beanpublic LettuceClientConfigurationBuilderCustomizer lettuceClientConfigurationBuilderCustomizer() {return builder -> builder.readFrom(SHENZHEN.equalsIgnoreCase(idc) ? ReadFrom.SLAVE_PREFERRED : ReadFrom.MASTER);}}
application 配置
spring:redis:sentinel:master: newredis_001nodes: wx-sentinel.test.com:20071,sz-sentinel.test.com:20071timeout: 600mslettuce:pool:max-active: 200min-idle: 5max-idle: 50time-between-eviction-runs: 300smax-wait: 500ms
ReadFrom 配置
所有除了MASTER外的ReadFrom配置都可能返回旧数据。因为副本复制是异步的，并且需要一些延迟
| Setting | Description |
|---|---|
| MASTER | Default mode. Read from the current master node. |
| MASTER_PREFERRED | Read from the master, but if it is unavailable, read from replica nodes. |
| REPLICA | Read from replica nodes. |
| REPLICA_PREFERRED | Read from the replica nodes, but if none is unavailable, read from the master. |
| LOWEST_LATENCY | Read from any node of the cluster with the lowest latency. |
| ANY | Read from any node of the cluster. |
| ANY_REPLICA | Read from any replica of the cluster. |
参考文档：
- SpringBoot中Redis Sentinel模式下读写分离
- Read from settings
