rfc - a preferred slave list in a sentinel setup

We want to run a sentinel setup:

• each webserver has it’s own redis slave (will NOT become master - using slave-priority = 0)
• a set of sentinels running to protect us from partioning and handle the quorum
• a master and a few redis slaves for failover of master

In the current implementation , the slaves can be selected using the role slave but it picks a rather arbitrary slave. We would propose to have a way to indicate a list of preferred slaves for a client.

This is useful is in multi-AZ aws setups, where we want to keep the latency to app<->slave low . A new syntax could look like:

var redis = new Redis({
  sentinels: [{ host: 'localhost', port: 26379 }, { host: 'localhost', port: 26380 }],
  preferred_slaves: [ { prio: 10 , host: 'localhost', port: 6381 }]
  name: 'mymaster'
});

[luin]

Makes sense. Besides a list of preferred slaves, I think we may also accept a function to let user pick up the slave:

var redis = new Redis({
  sentinels: [{ host: 'localhost', port: 26379 }, { host: 'localhost', port: 26380 }],
  preferredSlaves: function (availableSlaves) {
    return _.sample(availableSlaves);
  },
  name: 'mymaster'
});

[doublesharp]

@tangxinfa @jedi4ever this is now included in 2.4.0 😃