While for our rpm/koji builders we're relying on internal mirror (both for distro or other repositories like epel, etc), we'll be using soon (due to DC move and so hardware split) hybrid cloud models, and so with some EC2 instances running from an isolated VPC.
We should just redirect these hosts to either internal mirror (but would waste some hard disk space for things that would not even be asked for, like .iso images, or pkgs not needed a build time)
Instead we should just use a caching server that would :

• act as local mirror, but would fetch from origin
• put files/artifacts in cache (disk) for most frequently requested files (hot-cache)

We can probably just use nginx for that (we used that a long time ago , but configured through puppet) so time to revisit that and test this