502 / 503 — the front door is up, the thing behind it isn't
What is this error?
A proxy or edge server took your request and could not get a healthy answer from the application behind it.
Common Causes
- The app crashed on boot or exceeded its memory limit.
- A serverless function exceeded its time limit.
- The service is deploying or restarting.
- The app is listening on the wrong port.
How to fix it (Check First)
- 1Deployment logs: did the process start successfully?
- 2Is the failing request a long-running one? Check function timeout limits.
- 3Wait 60 seconds and retry — if it's a deploy, it self-resolves.
What NOT to do
- Do not spam redeploys during an active deployment.
Technical Details
502 is an invalid upstream response; 503 is upstream unavailable. Both are emitted by the reverse proxy, so your application logs may contain nothing at all.