"logging to CLI" I'm surprised it took this long. Getting HAProxy logs from docker has been a pain since you needed a volume mount and needed to export logs via a custom location, or you could go the hacky way and run a script that runs haproxy in the background and instead tails the log file.
haproxy 1.9 added support for logging to stdout/stderr/files, this is a different feature.
This feature looks like it is intended for cases where you're logging to a remote syslog server without any local log files and want to attach to the process and see the live recent logs which it stores in a ring buffer.
Yes it's exactly this. It's in fact a byproduct of the rings implemented for the trace subsystem making it trivial to log there, which turns out to be extremely convenient for embedded systems or inside containers even if logs are already sent to stdout and piped to docker or anything else.
