HAproxy - When does a backend throw an 50x error?

Question

I've setup a backend with a bunch of servers as well as backup servers like that:

backend <mybackend>
  mode http
  option allbackups
  balance roundrobin
  option http-server-close
  option httpclose
  server <my-server>     <my-ip>:80 check inter 5000 maxconn 20 rise 1 slowstart 30s weight 100
  server <my-server>     <my-ip>:80 check inter 5000 maxconn 20 rise 1 slowstart 30s weight 100
  server <my-backup-server>      <my-backup-ip>:80 maxconn 200 backup
  server <my-backup-server>      <my-backup-ip>:80 maxconn 200 backup

Today there was an outage and it showed up a basic 503 error instead of the setup backup-server maintenance page.

Now I need to know why that happens and when that happens. So what did I wrong?

score 0 · Answer 1 · answered Sep 24 '21 at 08:50

The answer is simple: When the backend hosts are not reachable the lb throws a 40x or 50x error. If a backup server solution is set, it serves that content.

The failure was that I didn't have the backup serves added on that lb pair. It only was on another one. So my example was wrong for my reality use case. But the setup above shows how a backup solution would work.

HAproxy - When does a backend throw an 50x error?

1 Answers1