502 Bad Gateway | HTTP Status Code

Explanation

The 502 (Bad Gateway) status code indicates that the server, while acting as a gateway or proxy, received an invalid response from an upstream server it accessed in attempting to fulfill the request.

This error typically occurs in the following scenarios:
- When a proxy or gateway server cannot access the upstream server
- When the upstream server returns a response that the proxy doesn't understand or considers invalid
- When the upstream server is down, overloaded, or experiencing a failure
- When the connection between the proxy and upstream server times out

This error is distinct from a 504 (Gateway Timeout), which specifically indicates that the upstream server did not respond in time. A 502 indicates that there was a response, but it was invalid or corrupted in some way.

Example Response

HTTP/1.1 502 Bad Gateway
Content-Type: text/html

<html>
<head>
<title>Bad Gateway</title>
</head>
<body>
<h1>Bad Gateway</h1>
<p>The proxy server received an invalid response from an upstream server.</p>
</body>
</html>

Related Status Codes

500 500 Internal Server Error 503 503 Service Unavailable 504 504 Gateway Timeout