Allow randomization of read candidates using Redis Cluster

Bug Report

Current Behavior

I am trying to connect to Redis cluster with 5 slave nodes and 1 master. All read queries are redirected to only one slave throughout the application scope.

Input Code

• Java/Kotlin/Scala/Groovy/… or Repo link if applicable:

// connection pool creation:
GenericObjectPool<StatefulRedisClusterConnection<String, String>> connectionPool;
GenericObjectPoolConfig poolConfig = new GenericObjectPoolConfig();
            poolConfig.setMinIdle(8);
            poolConfig.setMaxIdle(8);
            poolConfig.setMaxTotal(16);
            poolConfig.setMinEvictableIdleTimeMillis(1000*30);
            poolConfig.setSoftMinEvictableIdleTimeMillis(1000*30);
            poolConfig.setMaxWaitMillis(0);
            connectionPool = ConnectionPoolSupport.createGenericObjectPool(() -> {
                logger.info("Requesting new StatefulRedisClusterConnection "+System.currentTimeMillis());
                return redisClient.connect();
                }, poolConfig);

// 
public StatefulRedisClusterConnection<String, String> getConnection() throws Exception{
   StatefulRedisClusterConnection<String, String> connection =connectionPool.borrowObject();
   connection.setReadFrom(ReadFrom.SLAVE);
    return connection;
}

Expected behavior/code

It should distribute read queries on all slaves.

Environment

• Lettuce version(s): 5.1.0.M1
• Redis version: 3.2.10

Possible Solution

Additional context

[adityak93]

@mp911de @smoomrik AWS has recently introduced reader endpoints for Redis which manages distribution of reads among the slaves. You can check more details here: https://aws.amazon.com/about-aws/whats-new/2019/06/amazon-elasticache-launches-reader-endpoint-for-redis/

Might want to check this out. Using this should help avoid having to provide individual replica endpoints in the application giving more flexibility.
Not sure about exact underlying implementation of this on AWS side. Waiting for more clarification. Initial tests which we have done on test environment (1 master, 2 replicas) showed roughly equal distribution of load among the 2 replicas

[stillerrr]

Just give advice, if some one uses the lettuce like this, he need pay attention to increasing the refresh period or set “false” for refresh. no need to change the code. thanks : )