Docker definitely solves the problem imperfectly, though. Docker images simply don't compose, and this has caused me great pain: if you want image A plus image

Docker definitely solves the problem imperfectly, though. Docker images simply don't compose, and this has caused me great pain: if you want image A plus image B, you can't do much better than a multi-stage build where you just magically know what you need to pull out of the first image. Nix, by contrast, composes perfectly, because packaging something for Nix involves precisely specifying what you need (as opposed to packaging something for Docker, which involves… splurging your package arbitrarily across a clean container).