Most of the current Docker images for Swift involve starting from an Ubuntu base image, adding in various dependencies, then pulling a Linux toolchain from swift.org.
There is an alternate approach, which is not to pull prebuilt binaries, but to actually compile a toolchain (i.e. run utils/build-script) as part of the Dockerfile. This is the approach taken by @Drew_Crawford1 in his repo (well worth a look).
What do people think about this?