Apparently, this only happens if rsyslog is not installed. Which it is,
on normal Debian systems, as it can coexist happily with journald. I was
using a "lightweight" (=lacking features one would expect) container
installed from LXC's template that did not ship with rsyslog.
It's a little confusing that haproxy's startup logs go to journald, and
later logs go to rsyslog. I guess there is not much to do about that.
Maybe haproxy should explicitly depend on rsyslog for now.
--
Best Regards,
Anton Eliasson