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504 Gateway Timeout Explained: When Servers Get Stuck Communicating


  • RFC 9110
    This is a reference to the document that defines the current standard for HTTP. It specifies the meaning and usage of the 504 code among others.
  • 504 Gateway Timeout
    This specific code belongs to the 5xx class of codes, which indicates server-side errors. A 504 error means a server acting as an intermediary (gateway or proxy) didn't receive a timely response from another server it was relying on to fulfill the original client request.
  • HTTP Status Codes
    These are codes used to indicate the outcome of a communication between a client (like your web browser) and a server (like a web server).

While the user sees the 504 error, the problem lies in the communication between servers. There isn't specific programming code that generates a 504 error on the server itself; it's a result of a timeout mechanism.


  • 4xx Client Errors
    These indicate issues with the request itself, often due to user errors. They aren't directly related to 504, but can be helpful for troubleshooting:

    • 404 Not Found
      The requested resource couldn't be found on the server.

  • 5xx Server Errors
    These all indicate errors originating from the server-side. Examples include:

    • 500 Internal Server Error
      A generic error message indicating the server encountered an unexpected issue and couldn't complete the request.
    • 502 Bad Gateway
      Similar to 504, but occurs when a bad response is received from the upstream server.
    • 503 Service Unavailable
      The server is currently unavailable due to maintenance or overload.

  • 503 Service Unavailable
    If the timeout resulted from the upstream server being overloaded or under maintenance, this code might be a better choice.
  • 502 Bad Gateway
    This code can be used if the upstream server sent a bad or unexpected response that caused the timeout. It provides a slightly more detailed picture of the issue.

Here are some other options depending on the cause of the timeout:

  • Custom Error Messages
    While not technically a status code, some servers might provide custom error messages with the 504 response that offer more specific information about the cause of the timeout.
  • Retry After
    This header can be included with the 504 response to suggest a time for the client to retry the request.