---
title: "502 Bad Gateway — what it means and how to fix it"
description: "A proxy or gateway reached the server behind it and got back a broken response, or none at all. What causes an HTTP 502, what to try as a visitor, and what to check if it is your own site."
url: https://atoneplace.net/error/502/
site: "At One Place"
---

# HTTP 502 — Bad Gateway

**HTTP 502: Bad Gateway**

A proxy or gateway reached the server behind it and got back a broken response, or none at all.

## What 502 actually means

Your request reached a server acting as an intermediary — a CDN, load balancer, or reverse proxy such as Nginx — and that intermediary could not get a usable answer out of the machine actually running the site. The front door is working; the thing behind it is not. Because the proxy is healthy enough to generate an error page, a 502 almost always means the application process has crashed, is still starting up, or is not listening where the proxy expects it to be.

## Common causes

- The application process crashed or was killed, often by the out-of-memory killer
- The app is listening on a different port or socket than the proxy configuration points at
- The upstream returned a malformed response the proxy could not parse
- A PHP-FPM pool with no free workers, so connections are refused
- A firewall or security group blocking traffic from the proxy to the application
- DNS for the upstream host failing or resolving to a stale address
- The application restarting during a deploy, with no connection draining

## If you're just trying to view the page

1. Wait a minute and reload — deploys and restarts produce short bursts of 502s that clear by themselves
2. Hard refresh (Ctrl+F5 or ⌘ + Shift + R) in case a broken response was cached
3. Check the site's status page or Downdetector to confirm it is not just you
4. Nothing else — this is entirely a server-side fault

## If it's your site

1. Confirm the application process is actually running, and read its log for the crash that preceded the 502
2. Check the proxy's error log for the specific reason — Nginx will say "connect() failed (111: Connection refused)" or "upstream prematurely closed connection", and those point at different problems
3. Verify the upstream host and port in the proxy config match where the app is bound; binding to 127.0.0.1 when the proxy is on another host is a classic
4. Look for OOM kills in `dmesg` or `journalctl -k`; a memory leak shows up as periodic 502s
5. For PHP-FPM, check `pm.max_children` and the slow log — an exhausted pool refuses connections
6. Increase `proxy_read_timeout` only if the upstream is slow rather than dead; otherwise you are hiding a 504
7. Use health checks and connection draining so deploys do not drop in-flight requests

## Reference

- **Status code:** 502
- **Reason phrase:** Bad Gateway
- **Category:** 5xx — Server Error
- **Cacheable by default:** No
- **Defined in:** RFC 9110 §15.6.3

## Common questions

### What does HTTP 502 mean?

A proxy or gateway reached the server behind it and got back a broken response, or none at all. Your request reached a server acting as an intermediary — a CDN, load balancer, or reverse proxy such as Nginx — and that intermediary could not get a usable answer out of the machine actually running the site. The front door is working; the thing behind it is not.

### How do I fix a 502 error?

Wait a minute and reload — deploys and restarts produce short bursts of 502s that clear by themselves

### Is 502 a client error or a server error?

502 is in the 5xx range, which means server error. The request was acceptable but the server could not fulfil it, so retrying later can succeed.

## Related pages

- [500 Internal Server Error](https://atoneplace.net/error/500/)
- [503 Service Unavailable](https://atoneplace.net/error/503/)
- [504 Gateway Timeout](https://atoneplace.net/error/504/)
- [524 A Timeout Occurred](https://atoneplace.net/error/524/)
- [521 Web Server Is Down](https://atoneplace.net/error/521/)
- [522 Connection Timed Out](https://atoneplace.net/error/522/)
- [520 Web Server Returned an Unknown Error](https://atoneplace.net/error/520/)
- [525 SSL Handshake Failed](https://atoneplace.net/error/525/)
- [526 Invalid SSL Certificate](https://atoneplace.net/error/526/)
- [530 Origin DNS Error](https://atoneplace.net/error/530/)
- [501 Not Implemented](https://atoneplace.net/error/501/)
- [511 Network Authentication Required](https://atoneplace.net/error/511/)

## Sources

- Hypertext Transfer Protocol (HTTP) Status Code Registry — IANA (https://www.iana.org/assignments/http-status-codes/)
- RFC 9110: HTTP Semantics — IETF (https://www.rfc-editor.org/rfc/rfc9110.html)