In the docs page The Fly Runtime Environment · Fly Docs , under Fly-Client-IP it says:
Client IP Address : The IP address Fly accepted a connection from. This will be the client making the initial request and as such, will also appear at the start of the
X_FORWARDED_FOR
addresses.
The X_FORWARDED_FOR
capitalization is confusing, as it looks like an environment variable, but instead it’s a request header, so it should probably be X-Forwarded-For
.