Put one of these lines in /etc/apk/repositories, replacing the main line of an official mirror:
https://cdn-origin.net/pub/alpine/v3.22/main
https://cdn-origin.net/pub/alpine/v3.21/main
Only main is carried. Keep the community line pointing at an official mirror, or drop it if you do not need it.
Quick check that a branch is reachable:
curl -sI https://cdn-origin.net/pub/alpine/v3.22/main/x86_64/APKINDEX.tar.gz
The same tree is reachable through a CDN edge at cdn-origin.net; larger downloads are pointed there to keep load off this box.
The tree is pulled from rsync.alpinelinux.org every six hours. Upstream's own last-updated file is copied next to the tree; compare it with the same file on an official mirror if you want to know how far behind this copy is.
No rsync daemon, no FTP, no community/testing, no architectures other than x86_64, no release images. Those paths return 404 rather than an empty directory.
A tree may be briefly inconsistent while a sync run is in progress; runs use a staging directory and switch at the end, so this window is short. Access logs are truncated to the network prefix and rotated after 14 days.