Logstash will queue output if output is unreachable.
If during this time logstash gets a shutdown the entire queue is lost.
Would like periodic saves of output to file and upon restart if file exists, import into memory. Or option to save output queue backup to REDIS or some other queue medium.
So for example you have REDIS input -> ES output. all items are read from REDIS and are sitting in LS indexer. If ES becomes unavailable items will queue locally in memory. If logstash is restarted or killed at all before ES comes back up and output can be drained all events are lost.