Amazon is displaying a custom 404 page so any page that is not found gets the customer error. You can do this on your server by changing the 404 page the server send back. You can also do this at the f5. If the status code from the server is a 404. You can host the error page on the f5 instead of sending it to a pool of server. Doing this will allow you to send the same page for 500/400 and server down errors. The following link will walk you through the process.
https://devcentral.f5.com/articles/hosting-sorry-error-or-maintenance-pages-on-big-ip-ltm-with-irules.UmFPRRD4KSo