You just put the URLs you want Caddy to handle in the Caddyfile!
Like:
service1.mainframe.rulinglife.com {
proxy / service1
}
service2.mainframe.rulinglife.com {
proxy / service2
}
If you want to catch all the stragglers for random sub-subdomains you aren’t expecting, you can do that:
*.mainframe.rulinglife.com {
redir https://google.com
# Maybe grab a wildcard cert so this just works for HTTPS regardless of the hostname?
# tls {
# dns cloudflare
# }
}