[techman9]

> No messing around with virtualenvs and requirement files. Everybody builds with the same dependency versions. No more “works on my machine” and “did you install the latest requirements?”.

While this is nice, of course, I'm not sure that is outcome is unique to Haskell/Stack. It seems like you could accomplish a similar level of reproducibility by building a Docker image or bundling dependencies in some other way.

[Ruud-v-A]

We are actually using Docker for generating the virtualenv that we ship and running tests now. The motivation for doing this is being able to control the environment; we can run tests and build a package on CI, and we can build the same package locally when CI is down. We don’t use Docker in production.

It is not clear to me how Docker solves the issue of pinning dependencies; I would rather have a file that states the exact version of every package to install, than an opaque blessed container image that has some versions installed, and I do want to have the versions used under source control. Generating the image would not be reproducible (in the sense of having the same Python files inside it) without pinning versions somewhere anyway, right? Or am I missing something obvious?

[seagreen]

My understanding is that Docker only stays reproducible if after every change you kill the container and start a new one. Otherwise a particular change may only be working because of a side-effect of a change you introduced earlier and then deleted.

This isn't a huge issue, but still it's nice in declarative systems like Stack and NixOS not to have to worry about that kind of thing.