HAProxy Config – How to Reload on CentOS with Minimal Downtime?

centoshaproxy

When I change haproxy.cfg, currently I am "applying" those changes by running this command on CentOS:

systemctl restart haproxy

Is there a better way to do this on CentOS that does not involve downtime, or minimum downtime (or connection resets)?

Use reload instead.

systemctl reload haproxy

I sent an e-mail to Willy Tarreau and got back the following options:

You can use hot reconfiguration or socat commands to the stats server to set the weight of your target server to 0. This will prevent new sessions from being balanced to that server, but won't affect existing connections.
You can set the http-check disable-on-404 option in combination with "option httpcheck /myurl" and then have your target servers respond to /myurl such that they send a 200 status if everything is fine, a 404 if the server should stop receiving new requests, and a 500 if the server should receive nothing (i.e. when you're ready to bounce the server). haproxy will re-check on the server at the interval specified in your server line.

iptables -I INPUT -p tcp --dport $PORT --syn -j DROP
sleep 1
service haproxy restart
iptables -D INPUT -p tcp --dport $PORT --syn -j DROP

This has the effect of dropping the SYN before a restart, so that clients will resend this SYN until it reaches the new process.