Resolves a bug with cluster where a subscribe is sent to a disconnected node

[devaos]

The issue came up when connecting to a load balancer, sitting in front of the redis cluster nodes, and attempting to subscribe as soon as the 'ready' event was fired. The load balancer's IP:port is not in redis cluster's list of nodes so the connection was disconnected and removed, causing the subscribe to be sent to the disconnected node.

[luin]

When a node is disconnected(https://github.com/luin/ioredis/blob/master/lib/cluster.js#L407), ioredis will re-select a new subscriber automatically(https://github.com/luin/ioredis/blob/master/lib/cluster.js#L164). So you don't need to call selectSubscriber manually.

[devaos]

Oh, I see what you mean. However this commit did resolve the issue we were having. I'll comment shortly with the debug logs so you can see what was happening.

[devaos]

Here is a snippet of the debug output before the patch. I added a couple console lines to clarify which command was being sent and whether the stream was writable.

  ioredis:redis status[127.0.0.1:6381]: close -> end +1ms
  ioredis:redis status[10.240.14.47:6375]: connect -> ready +0ms
  ioredis:redis status[10.240.46.240:6375]: connect -> ready +0ms
  ioredis:redis status[10.240.75.76:6375]: connect -> ready +1ms
  ioredis:redis status[127.0.0.1:6381]: ready -> close +0ms
  ioredis:connection skip reconnecting since the connection is manually closed. +0ms
  ioredis:redis status[127.0.0.1:6381]: close -> end +0ms
  ioredis:cluster getting slot cache from 10.240.46.240:6375 +2s
sendCommand: command.name=cluster
sendCommand: stream.writable=undefined
sendCommand: this.stream.writable=true
  ioredis:redis write command[0] -> cluster(slots) +1ms
sendCommand: command.name=subscribe
sendCommand: stream.writable=undefined
sendCommand: this.stream.writable=false
  ioredis:cluster getting slot cache from 10.240.46.240:6375 +2s
sendCommand: command.name=cluster
sendCommand: stream.writable=undefined
sendCommand: this.stream.writable=true
  ioredis:redis write command[0] -> cluster(slots) +0ms
sendCommand: command.name=subscribe
sendCommand: stream.writable=undefined
sendCommand: this.stream.writable=false

[devaos]

I updated the commit with what I believe is a more appropriate fix based on your feedback. Thanks

[luin]

Awesome! Thank you for the patch!