until you need to start combining things. Docker is conceptually a VM the encapsulates everything nicely, but it ironically doesn't "compose" nearly as well as nix flakes or shells. With Nix you start out with a base env and can trivially extend it hierarchically and jump up and down the tree super easily, and without having to roll your own microservice architecture each time just to get stuff to work together.

Docker OTOH composes whole services nicely: if my project needs a redis cache and postgres instance, I don't have to faff about with local ports, traefik can pick up my web server, and so on. I use a flake to create and lock a local development toolchain, but it's no help in managing the services.

One thing I haven't tried yet is building a container from a flake, which would have obvious benefits for reproducibility. Still don't think it would help with service orchestration though.