Why is Debian connecting to a CDN server in the background, automatically?

I noticed my VM with a fairly barebones Debian 11 install periodically tries to connect to debian.map.fastlydns.net on port 80. It looks like this domain is what the DNS record of http://deb.debian.org points to (and has [for at least a year](https://old.reddit.com//r/debian/comments/kexgjr/domain_debianmapfastlydnsnet_really_debianrelated/)) , so it seems to be a legitimate request somehow related to package update tracking. But what is doing this? Debian doesn't have a MOTD showing available updates, and it usually seems to need manual running of apt update and apt upgrade to keep the system current. Could I opt-out of whatever service(s) cause these requests?