[airhead969]

I know all about application file systems overlays, I was part of a startup that shipped a multiplatform one. They have many many problems because they blow in a fixed set of dependencies as a monolith. It's a similar to the difference between image-based deployment and configuration management-based deployment: granularity of lifecycle including updates, and management.

The nuances become readily-apparent running anything real at scale, especially if you're only given a herring (Docker) to chop down the mightiness tree in the forest when you need a harvester (hypervisor). Docker, flatpak, and snap are unnecessary other than as shiny, fragile toys that attempt to (poorly) replicate the functionality of other tools. Live migration for containers is like adding high availability to a solar calculator: completely pointless and inappropriate engineering. Just don't get attached to these limited "advances" / fads / religions because popularity and newness aren't the same as demonstrable progress.

It's better to use something like Nix or habitat for multiversion app dependencies or just privately vendor them. There is no need for snap or flatpak if a containerizable OS can choose the correct dependency constraints for an app. The problem of concurrent package versions in existing package management systems can be solved with naming and numbering standards rather than reinventing everything.