HTTP 502 — glossary
TL;DR
Bad Gateway — upstream did not return a valid response.
Key facts
- Term
- HTTP 502
TL;DR
HTTP 502 Bad Gateway means your reverse proxy received an invalid or empty response from upstream — usually PHP-FPM, Node, or Gunicorn is down, saturated, or misconfigured.
Common causes
- All FPM workers busy (
pm.max_children) - Wrong socket path after deploy
- Upstream crash loop after OOM
See the full 502 Bad Gateway guide.