Apache comes with a directive to allow administrators to customise the error message for any error, as specified by its number. For example, the error number for a Bad Gateway is 502, therefore the directive:

should change the Bad Gateway message to whatever is specified in the file error502.html.

All would be well, you would think, except for the fact that all of our Plone hosting uses mod_rewrite, which would produce an apache vhost config such as this:

Unfortunately if you try this out you will (rather ironically) get another 502 error message whilst trying to serve the 502 error message:

"Additionally, a 502 Bad Gateway error was encountered while trying to use an ErrorDocument to handle the request."

The reasons for this are rather obvious: the request error502.html is also going to be rewritten, and since nothing under http://192.168.131.85:13080 is going to work (because the Zope instance is down!) this produces another 502.

One workaround is to use an absolute URL in the ErrorDocument directive, e.g.

but we didn't like this because this causes a browser redirect, so the visitor loses the URL they entered into their browser, which is very annoying if you want to keep refreshing to find out when the site comes back up. Also the redirect code is confusing for search engines:

"the client will not receive the original error status code, but instead will receive a redirect status code. This in turn can confuse web robots and other clients which try to determine if a URL is valid using the status code."

Therefore we wanted a workaround that avoided this. The solution we came up with is to add a RewriteCond to exclude error502.html thus:

in words this means "Rewrite all URLs to the zope instance, unless the URL is error502.html". This now works perfectly. Problem solved. It's odd I haven't seen this solution elsewhere on the web.