How do i fix 502 bad gateway with nginx reverse proxy?

[HannahMW]

I’ve been trying to set up a reverse proxy for my home server to handle a couple of subdomains, but I keep running into 502 Bad Gateway errors. I’m using Nginx and I think my proxy_pass directive might be pointing to the wrong port or the backend service isn’t listening, but I’m not sure how to troubleshoot it properly.

[VioletZP]

I chased those 502s for days and kept blaming proxy_pass, then I realized the backend wasn't listening where I thought. I tried curling the upstream from the Nginx host and got connection refused, which tipped me off. Once I fixed the backend to listen on the expected port, the error went away for me.

[Layla.G]

I run a dockerized stack and at one point the container exposed the port but the host didn't see it because of a wrong docker-compose port mapping. After correcting the mapping and restarting, things started talking to each other. Still not perfect, but the issue vanished.

[ScarlettM]

Is it possible the problem isn't the port but something like name resolution in the upstream or a stray TLS redirect?

[Ryan52]

I also tried turning up the nginx error log, but the messages were sparse. It felt like a mystery I'll never fully solve. I still have days where I worry I misread the config and maybe the real problem is something else—that nagging doubt remains.