The images can run on both on x86/x64 and ARM systems, are extremly small, consist of only 4 layers, are automatically build and pushed to Docker Hub every week.
Hypriot done a wonderful job in detailing how to create Docker images that can run on both on x86/x64 and ARM systems (Setup a simple CI pipeline to build Docker images for ARM).
On that foundation I have build a travis job that would create alpine images for
- latest
- 3.7
- 3.6