Fastly is not "some backend tool". Two seconds of Google'ing would reveal to you that they're a Content Distribution Network, aka CDN. They're the ones actually

Fastly is not "some backend tool". Two seconds of Google'ing would reveal to you that they're a Content Distribution Network, aka CDN. They're the ones actually serving the content hosted on *.github.io: host user.github.io user.github.io is an alias for github.map.fastly.net. github.map.fastly.net is an alias for prod.github.map.fastlylb.net. prod.github.map.fastlylb.net has address 151.101.12.133 Cloudflare doesn't act as a CDN in this case. What Cloudflare does is proxy the request for you, and by virtue of them terminating the request they can serve an SSL certificate for your domain (either handed out by them or custom if you pay them).