504 Gateway Timeout is an HTTP status code that indicates a server acting as a gateway or proxy did not receive a timely response from an upstream server.

Here are some specific reasons why a 504 Gateway Timeout HTTP status code may be returned:

  • The gateway server acting as a proxy or load balancer fails to get a response from an upstream application server or microservice within the allotted time threshold while waiting for a full response.
  • There is an overloaded application server behind the gateway that is working too slow to fully construct responses to client-originated requests within the gateway’s configured response timeout window.
  • A DNS, database, or other external service that the backend application relies on to build responses is operating too slow in providing critical pieces of data the gateway needs.
  • Security services like WAFs or authentication layers between the gateway and application servers contribute additional latency that exceeds timeout thresholds while processing requests and responses.
  • The network connection between decoupled gateway and application server tiers suffers packet loss, high jitter, or connectivity issues that degrades transmission performance below timeouts.
  • The application is functioning correctly but the timeouts configured on the intermediary gateway are too aggressive for the normal behavior patterns.

In summary, 504 errors stem from inadequate response times of systems behind a gateway to enable fully proxying application behavior within permissible time boundaries.