[xiaodown]

I mean, "apachectl graceful" has existed for 20+ years. Sending a graceful (USR1) to apache will cause it to re-read its config, close and re-open log files, and send a signal to all children that they should exit after their current work is finished. If they have no work, they die immediately. New children are created under a master process that has the new configuration.

I know that HAProxy is not an apples to apples comparison with something like apache, but I don't see how something similar would be a huge burden to add.

[tyingq]

A multi-protocol (way more than http) load balancer with health checking just has more state than a web server. Check bug history for apache, and you'll see that modules that deal with state, like mod_security, have had issues with graceful reload in the past.

It's not that surprising to me, especially given that haproxy is 17 years old. Expectations of a load balancer where pretty light when it was invented, so the internals weren't built for hot reload.

[nollbit]

If you can restart without downtime you don't need a hot config reload. Suddenly you can treat config as immutable and discard an entire category of bugs as well.