@kiokoman said in HAProxy: 503 errors on 2 domains:
@oguruma
HAproxy 503 Service Unavailable No server is available to handle this request is passed when the http check fail for some reason even if the service is up and runninglike in this post https://serverfault.com/a/886319
you need to adjust that option in a way that it receve a valid response from the server or disable httpchk
Thanks again for the help. I got it working by deleting both the frontends and the backends for the not-working domains and recreating them, making sure to disable health checks from the outset when creating the backends.
One thing that is curious is that I re-installed ERPNext on separate, vanilla VM and pointed the backend to that new VM with healthcheck enabled, and it worked fine...