Basically, you’re running HAproxy 1.7.x on Debian/Ubuntu and have no logging under /var/log or you’re getting log files full of errors like:
haproxy-systemd-wrapper  sendmsg logger #2 failed: Connection refused
There are many reasons for this problem, but most of the solutions are related to standard setups, which means if you have version 1.7 by the time this post is published, you’re not getting the binaries through standard apt-get libraries. Thus, you don’t have standard setup ;)
Anyway, if you’ve installed version 1.7 directly, then simply remove it, and remove pointers in apt-get libraries to its source.
Install version 1.6 from the standard libraries, and test the functionality of HAproxy, then test the functionality of the logging.
Finally, you can upgrade to version 1.7 and logs will keep working for you.
Don’t ask me why, I don’t have time to find the root cause :)