Available inall subroutines.
The Fastly IP address used to connect to the backend server in a backend request.
For most connections, this will be one of the most frequently used Fastly server IP addresses used for default routes across the Internet. If the origin rerouting mechanism, part of our Precison Path product, was triggered by a problem with the original connection attempt over the default route, then this value will show an alternate Fastly server IP address from a pool of IPs reserved for alternate routes between that POP and your origin.
beresp.backend.alternate_ips provides a list of the possible IP addresses available to originate origin connections for the active request.