HTTP Status Code 504 – Gateway Timeout

The HTTP status code 504 Gateway Timeout indicates that a server, acting as a gateway or proxy, did not receive a timely response from an upstream server it needed to access in order to complete the request. This status code suggests a network or server-side issue where the target server is not responding quickly enough. It is a server-side error, classified among the 5xx status codes.

Example 1: Web Server as a Proxy

Consider a scenario where a client makes a request to a web server, which acts as a proxy to fetch data from a database server. If the database server takes too long to respond, the web server might return a 504 Gateway Timeout error to the client:


Client ---> Web Server (Proxy) ---> Database Server
↑
504 Gateway Timeout


In this example, the client does not receive the expected data because the database server failed to respond in time, leading to a 504 error from the web server.

Example 2: Load Balancer with Multiple Servers

Imagine a load balancer distributing requests across several application servers. If one of these servers becomes unresponsive due to high load or a malfunction, the load balancer might return a 504 error when it fails to receive a timely response:


Client ---> Load Balancer ---> App Server 1 (Timeout)
↑
504 Gateway Timeout


Here, even though the load balancer could potentially route requests to other servers, if the chosen server doesn’t respond, a 504 error is returned.

Example 3 Scenario

# Client sends a request example.
GET /example HTTP/1.1
Host: www.example.com

# Server Response
HTTP/1.1 504 504 Gateway Timeout
Date: Wed, 09 Oct 2024 23:10:56 GMT
Server: ExampleServer/1.0
Content-Type: application/json

{
    "error": "Description of the error for 504"
}

Example 4 Scenario

# Client sends another example request.
POST /another-example HTTP/1.1
Host: www.example.com

# Server Response
HTTP/1.1 504 504 Gateway Timeout
Date: Wed, 09 Oct 2024 23:10:56 GMT
Server: ExampleServer/1.0
Content-Type: application/json

{
    "error": "Detailed message for 504"
}

Summary

The 504 Gateway Timeout error is typically caused by the inability of a server to receive a timely response from an upstream server it relies on to fulfill a request. Common causes include network congestion, server overload, or misconfigured firewall settings. To resolve such issues, it is important to investigate the server’s connectivity and performance, ensure proper configuration, and possibly increase timeout settings or load capacity.