Hi! I posted the issue from 19 days ago. I believe we actually do need asynchronous appending:
We have a setup with Elasticsearch logging to a Redis queue. Suppose the ES loglevel would temporarily be changed to DEBUG (or maybe even TRACE) and there would also be network issues in between ES and Redis. If a synchronous appender would be used, then in this setup the logging would actually render the cluster to be very slow/unresponsive because it would have to wait for all logs to be processed, before getting to continue its normal operations.
Or is there something I'm missing/does ES solve this in a different way?