This works great but there might be an edge case that fly should consider addressing:
if a machine that was set on the user’s cookie is destroyed, the request from that user will hang indefinitely. It looks like Fly replay isn’t making sure that the machine exists before replaying the request.
After about a minute or so, the request errors w/ 503. I’m guessing the Fly edge should also also expire the cookie, but that cookie key is user defined, so it’s not as straightforward.