At first I was confused as I know I can control my 404 as I had set it properly in my Web.Config file as such:
<httpErrors existingResponse="Auto"> <remove statusCode="404" subStatusCode="-1" /> <error statusCode="404" path="/?action=main.404" responseMode="ExecuteURL" /> </httpErrors>With the existingResponse attribute set to "Auto", it leaves the response untouched only if the SetStatus flag is set. Which I thought that meant as long as I set it in ColdFusion it would skip trying to show the IIS error page. Now, not to confuse further, the settings above worked for my 404s because I was removing how the server handled it and applying my own ExecuteURL setting. The issue was when i was trying to do a custom 503 (as FuseGuard shows when a request is blocked).
Now there is a value of PassThrough that can be set for existingResponse and it would work but the problem here is that if you have lets say a RewriteRule that blocks a request and sets it as a 503 nothing displays. So this was not going to work for me in that scenario.
More on IIS Custom Errors
Here is where TrySkipIisCustomErrors comes into play. Basically for existingResponse="Auto" to work properly we must be able to set Response. TrySkipIisCustomErrors to true but there is no way to do this in ColdFusion, trust me I tried hacking at it using getPageContext(). So then I started to google an alas there is a fix now for some of us.
While the solution can be found in either of the 2 following posts, you still have to search within the content to find it so I thought I would just show you and hopefully make future google searches a little easier.
As of ColdFusion 10 Updater 18 and ColdFusion 11 Updater 7 there is a new setting that you can find in your
isapi_redirect.propertiesfile for your connector that is called
iis_skip_custom_errors_enablewhich defaults to
false. Go into that file or files (if more than one connector) and set it to true. Restart your IIS site (ColdFusion does not have to be restarted) and like magic it all works now.
To get a visual of what I am talking about below is a before and after of what my 503 page was coming up like.
And since the setting is set to Auto, if nothing is set by ColdFusion, like one of my RewriteRules which blocks access to a certain directory, then the default IIS page is displayed as such.