I am using ECS for a webapp, and i setup an Error Pages definitions for codes 404 and 502. My current setup returns a static maintenance.html file (hosted on S3) and returns a code of 200. I have to return 200, otherwise Outlook (which hosts my app) will not render the returned html, and show an ugly error page instead. The problem I'm having with it, is that a later API call from my clientside app to my server, might also return 404. With the current setup, CloudFront intercepts this reply, and returns the maintenance.html with code 200. So now my app doesn't know anything is wrong, and later fails on parsing the reply.
Is there a way to define the Error Pages to only handle specific requests? For my usage, I'd like them to only handle calls to my /static/index.html files. If some other file/API call is actually missing from the server, I'd like my client to get the 404, so it can handle it properly.
So to answer your question according to the documentation I read there is currently no way to do this from cloudfront Error Pages Config.
However, We had a similar problem, but in our case API calls were returning a 500 Error with a s3 custom error html instead of the actual server error that I expected only for API calls.
What we ended up doing in this case was a handler in the back end for 500 errors that would return a response code that we were not using in the cloudfront Error Pages if the request Url had the pattern of API calls (we used http Error Code 406) and then the handler will reply with the 406 response code and the whole error instead of the 500 with the s3 response html only when failed over the api url pattern. I know this does not solve the problem the way you would have like to, but probably you may find it helpful until cloudfront allows a custom error response based in a Path Pattern.