NextCloud and HAProxy once working now mysteriously gives 503 error

I have had a functional NextCloud instance successfully self hosted and provided via HAProxy at Linode. All of a sudden in the last few days it’s started coming up with a 503 error. I have double and tripple checked everything on the HAProxy side and it all appears correct as far as I can see. No config changes had been made by me. I can still access the NextCloud instance via the public IP and exposed port (nonstandard port being used). I have checked fail2ban on both systems and don’t see any jail issues. I’ve been digging unsuccessfully to find a cause/solution for a couple of days. Anyone out there have any thoughts/suggestions on what might be going on and how to fix it?

Just bumping this up.

How is the nextcloud server deployed?

It’s deployed as a lxc via proxmox and is port forwarded from my firewall/gateway.The HAProxy handles the cert and traffic direction to the site. It works just fine via the ip:port that is defined in the HAProxy backend config. However if I go to the front end of the HAProxy I get a 503. Other sites handled through the same setup using different forwarded ports work just fine. I just can’t find any reason for the 503 all of a sudden.

Are you certain it’s connecting to the database properly?

You said the config on the Nextcloud server didn’t change.
Did you update your software or changed anything in haproxy?

As far as I am aware nothing was changed on either side. There are no issues with DB connection in nextcloud. If I connect to it without going through HA proxy, going to the address specified in the backend config it works just fine.

I think I finally fixed it. Seems that something non apparent got mangled in the LXC network config. Being frustrated and having no idea what could be going on I decided to delete and readd the network info at the Proxmox LXC config level. After doing that and restarting the container for the umpteenth time everything seems to be ok. The wierd thing is everything looked normal before both at the Proxmox level and from inside the container.
Can’t tell you how many hours I spent digging through all of the configs from start to finish on both the HAProxy side and the NextCloud side. Just frustration made me decide to rebuild all the network related configs from start to finish.

Thanks to those who responded.