Tuesday, 25 October 2011

HTTP Error 504 Gateway timeout


HTTP Error 504 Gateway timeout
Introduction
A server (not necessarily a Web server) is acting as a gateway or proxy to fulfil the request by the client (e.g. your Web browser or our CheckUpDown robot) to access the requested URL. This server did not receive a timely response from an upstream server it accessed to deal with your HTTP request.
This usually means that the upstream server is down (no response to the gateway/proxy), rather than that the upstream server and the gateway/proxy do not agree on the protocol for exchanging data.
504 errors in the HTTP cycle
Any client (e.g. your Web browser or our CheckUpDown robot) goes through the following cycle when it communicates with the Web server:
  • Obtain an IP address from the IP name of the site (the site URL without the leading 'http://'). This lookup (conversion of IP name to IP address) is provided by domain name servers (DNSs).
  • Open an IP socket connection to that IP address.
  • Write an HTTP data stream through that socket.
  • Receive an HTTP data stream back from the Web server in response. This data stream contains status codes whose values are determined by the HTTP protocol. Parse this data stream for status codes and other useful information.
This error occurs in the final step above when the client receives an HTTP status code that it recognises as '504'. Frank Vipond. September 2010.
Fixing 504 errors - general
This problem is entirely due to slow IP communication between back-end computers, possibly including the Web server. Only the people who set up the network at the site which hosts the Web server can fix this problem.

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