The Tails downloads are served using a HTTP mirror pool.
HTTP pool
The HTTP pool is a web service that redirects clients to the nearest mirror based on their IP geolocation data:
IP geolocation data is automatically and periodically updated from MaxMind's GeoLite2 databases.
Downloads are served under the
download.tails.netdomain (see mirror statistics).Mirrorbits performs the actual redirections according to its own internal score system, which is based on mirrors' weights and IP geolocation data (Autonomous Systems, countries and calculated distances).
The list of mirrors is maintained by Sysadmins via Puppet (see code and example data)