Comment by edude03
4 days ago
I'm not talking about a bit perfect reproduction though, just being able to understand dependencies. Take for example a simple Dockerfile like
``` FROM python:latest ADD . RUN pip install foo ```
If I run this today, and I run this a year from now, I'm going to different versions of `python` and `foo` and there is no way (with just the Dockerfile) to know which version of `foo` and `python` were intended.
Nix on the other hand, forces me to use a git sha[^0] of my dependency; there is no concept of a mutable input. So to your point it's hard to 'upgrade' from version a -> b in a controlled fashion if you don't know what `a` even was.
[0]: or the sha256 of the depedency which yes, I understand that's not easy for humans to use.
Well, what about "FROM python:3.18" and using requirements.txt or something like that? I mean, running an arbitrary Python version will get you in trouble anyway.
Depends on the repository used, actual version revision of Python, compiled features, the way the requirements file is written, the way the current version of pip resolves them, the base is that Python image and a lot of other things. Doing that gives you maybe 30% of the way towards something reproducible and consistent.
There's no mechanism to enforce this is done consistently. With nix, there is.
The degree to which this guarantee is useful or necessary depends on your use case.