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Help for HTTP error 504: “Gateway Timeout”

This HTTP error occurs when there is a gateway or proxy¹ between your web browser and a web server that you want to access (e.g. in your ISP) and the gateway experienced a time-out while waiting for a response from either the server that you are trying to access, or from an auxiliary server (e.g. a name server).

Outline: Symptoms Cause What you can do about it Extra information Footnotes

Symptoms

Microsoft Windows Update reports HTTP 504 status codes with error code 0x80244023 (hexadecimal 80244023).

Apache servers report this as:

Gateway Time-out
The proxy server did not receive a timely response from the upstream server.

(A footnote² expands on the meaning of “upstream”)

Cause

The official description of what causes the HTTP 504 status code is:

“The server, while acting as a gateway or proxy, did not receive a timely response from the upstream² server specified by the URI (e.g. HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed to access in attempting to complete the request.”

In that description,

“URI” can be interpreted as “URL” (Uniform Resource Identifiers that also indicate the Location of the resource),
“HTTP, FTP, LDAP” are protocols used for accessing resources, and
“DNS” is the Domain Name System that is used to translate names (e.g. www.example.com) into addresses that are used for communication.

What you can do about it

Try accessing the website through a (different) proxy. If the problem was particular to the gateway/proxy that you accessing the site through, then using a (different) proxy may³ allow you to bypass the earlier gateway/proxy.
These errors often arise because the proxy failed to resolve a domain name into an address. It might succeed if you try again, or if you can resolve the name (while the proxy can't, e.g. because it uses different name servers) then you might be able to access the server through its IP address.
If the problem is with the website that you are trying to access, then monitor it to determine when it returns to service.

Extra information

This is the gateway equivalent of the DNS/TCP errors that can occur a server that you try to access directly (without a gateway) does not respond in a timely manner, e.g. leading to the error Internet Explorer cannot display the webpage.

An alternative symptom of a proxy DNS timeout is a HTTP 400 error.

HTTP error 408 occurs in the complementary situation of a downstream server timing out while waiting for information from an upstream device (e.g. a web browser).

HTTP 502 errors also arise from gateway/proxy problems, but arise when an invalid response was received from a downstream server. Microsoft IIS may report a 502.1 error when the gateway times out waiting for a response from a CGI application.

Footnotes

¹ Although “Gateway Timeout” is usually reported as the reason for HTTP 504 errors, they can also arise from problems with proxies, which are slightly different from gateways in that they do not act like origin servers.
² Note that “upstream” here is in the context of the response, so the invalid response came from a server that was “downstream” of the proxy when the request was being sent.
³ Provided the earlier gateway/proxy isn't on part of the network that you can't bypass, e.g. mediating all traffic from your ISP or all traffic to the web server that you are trying to access.