One of the design principles of Sovereign Stack is to cache data early and often. If a request can be satisfied through a caching mechanism, then it will be. This improves performance and it also gives you better privacy since you're not making requests to wider internet.
Sometimes items are cached on the management machine such as LXD VM images or blockchain data. This is useful to push seed data to remote endpoints.
But you could also have a dedicated device on the SERVERS VLAN which is responsible for hosting cached docker images, LXD images, an apt and HTTP cache, etc. This set of network-based cache mechanisms can be deployed using a script. This is called the Cache Stack. Planned uses are:
2. Docker registry for hosting images that have to be built.
3. http proxy/apt-cache (squid)? https://help.ubuntu.com/community/Apt-Cacher NG
Cache Stack would be a separate repository and SHOULD be able to execute on a Raspberry PI or x64 device. The only dependency should docker (not compose, swarm, etc).