All HTTP status codes

HTTP 504 Gateway Timeout

Server Error

A gateway/proxy didn't get a response from the upstream in time. The upstream may still be processing — the proxy just gave up waiting.

Defined in RFC 9110

Common causes

  • Slow upstream work (long queries, external API calls) exceeding proxy timeout
  • Network path problems between proxy and upstream
  • Undersized connection pools causing queuing delays

How to fix it

  1. Profile and speed up the slow upstream operation; add DB indexes

  2. Move long work to async jobs (respond 202 + status URL)

  3. Align timeout budgets: client > proxy > upstream

  4. Check connectivity between the proxy and upstream

Related status codes

502 Bad Gateway

A gateway/reverse proxy got an invalid response from the upstream server — the proxy is fine, the thing behind it isn't answering properly.

408 Request Timeout

The server gave up waiting for the client to finish sending the request. Servers often close the connection afterwards.

503 Service Unavailable

The server is temporarily unable to handle the request — overloaded, in maintenance, or deliberately shedding load. Retry-After may say when to come back.

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