It's less common now, but for many years one of the more popular ways to DDOS someone was to trick a third party into sending them lots of data.
1,005 karma · joined August 9, 2010
edit:
Which are probably tailscale's, as it's under tailscale/ github org?
photos.example.com {
reverse_proxy 127.0.0.1:8080 {
header_up X-Real-IP {remote_host}
}
}