I'm running a simple test with 3 masters + 1 slave per master. If I take down one of the slaves and restart it, ioredis fails to reconnect to that node.

  ioredis:redis status[127.0.0.1:6421]: ready -> close +7s
  ioredis:connection skip reconnecting because `retryStrategy` is not a function +0ms
  ioredis:redis status[127.0.0.1:6421]: close -> end +0ms
Received -node: "127.0.0.1:6421"

Note, however, that retryStrategy is a function. I've repeated this failure with 1) no options supplied new Cluster, 2) with options, but not setting options.redisOptions.retryFunction and 3) with option, but setting options.redisOptions.retryFunction to function() { return 3000; }.

Even long after the node has been restarted and rejoined the cluster (verified with redis-cli cluster slots and cluster nodes), ioredis continues to report the cluster.nodes().length = 5.

So, the only way to recover from this very basic failure mode is for the application to monitor the '-node' event and destroy and re-create the client. This is a bad defect.

I would have hoped that ioredis was periodically monitoring the cluster configuration by periodically performing a cluster slots command, it is clearly impossible for ioredis to detect if new slaves are ever added to the cluster in an expansion scenario.