Why do I get 502 Bad Gateway with nginx reverse proxy to my node app?

[AlexanderMM]

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 on a VPS, and my backend is a Node.js app on a different port, but the requests just aren’t getting through.

[Mia_L]

I ran into this too. The upstream wasn't answering. My Node server was listening on 127.0.0.1:3001 but Nginx proxy_pass pointed at 3000. When I curl -s http://127.0.0.1:3000 from the VPS I got connection refused. After changing the port to the one Node actually used and restarting, the 502 vanished.

[BrianD]

I had a 502 once when the Node process kept dying on load due to an exception. I checked the logs, found a crash on startup, fixed a missing env var that pointed to a wrong DB URL, and restarted. The error didn’t show up after that, at least for a while.

[Matthew_G]

Are you sure the upstream port is reachable from the VPS? Have you tried curl from the server to the Node port to confirm?

[Aria.D]

I kept wandering through the SSL and headers, but often it was a stale Nginx config or a trailing slash in proxy_pass. I drifted off topic once and then came back to the same port mismatch habit, and it still felt unsettled.