Docker versus Singularity

[hvgazula]

Personal observations/experiences (will be haphazard):

1. What exactly is the end system (os, architecture. and others) we are designing no-brainer tools for? cluster or personal computers? linux/macos/windows or all of them?
2. This question arose because of some personal pain points experienced this week. The models already in the zoo were all built using pip install inside the dockerfile. However, @WilliamAshbee built his environment using conda, which means, we have to find ways to activate the environment as soon as we enter the container. While this has been easier in docker, not so much in singularity. And that too for a sif built from a docker image.
3. Going from docker to singularity is very very time-consuming. Docker is not available on HPC and macOS. Singularity needs VMs to work on windows and macOS. Using Github actions to build docker images is a good idea (thanks to @djarecka) but not so much for debugging because of the lack of caching. Waiting to hear from @dhritimandas about caching on nix/circleCI.