I have used lamdba@edge and our primary use case was to rewrite url (to add languages information for example) so I'm sure it works in viewer request events.
No. Please see the many other responses I gave to other comments. It does not work because the viewer request is the request the viewer views. If you change the URL of the viewer request, CloudFront sends a 301 accordingly. In other words, changing /api/blah to /blah in the "Viewer Request" part results in CloudFront injecting a `301 location: /blah` and the client doesn't hit your backend because they got redirected. The client instead hits your frontend as a result of your URL rewrite. There is a very clear difference between viewer and origin. If you could rewrite origin requests at the viewer level there would not be any difference between the two. This is the difference. Viewer is what the client sees. Origin is what the backend sees.
My understanding is that you would need to rewrite the url and update the origin.
I could be wrong as I did this lambda@edge a while ago, but the main difference between the two request event is that viewer request is done in all cases, while origin request is done only in case of cache miss.
[EDIT] you are right, updating the origin is indeed something that cannot be done on the viewer side. My bad, I should have checked earlier.
