Earlier this month I mentioned on Mastodon that I was replacing a Docker-based local development environment at my day job with a Nix-based one, orchestrated with overmind and a justfile. There was quite a lot of interest in particular in how overmind and just could be used to replace a container / compose-based local development. While I can’t share the details of the significantly more complex migration I did at my day job (yet!

Some folks on the internet were interested in how I had managed to ditch Docker for local development. This is a slightly overdue write up on how I typically do things now with Nix, Overmind and Just.

  • @[email protected]English
    7•1 year ago

    Docker builds are not reproducible

    What makes you say that?

    My team relies on Docker because it is reproducible…

    • @[email protected]English
      2•1 year ago

      You might be interested in this article that compares nix and docker. It explains why docker builds are not considered reproducible:

      For example, a Dockerfile will run something like apt-get-update as one of the first steps. Resources are accessible over the network at build time, and these resources can change between docker build commands. There is no notion of immutability when it comes to source.

      and why nix builds are reproducible a lot of the time:

      Builds can be fully reproducible. Resources are only available over the network if a checksum is provided to identify what the resource is. All of a package’s build time dependencies can be captured through a Nix expression, so the same steps and inputs (down to libc, gcc, etc.) can be repeated.

      Containerization has other advantages though (security) and you can actually use nix’s reproducible builds in combination with (docker) containers.

      • nickwitha_k (he/him)English
        10•1 year ago

        That seems like an argument for maintaining a frozen repo of packages, not against containers. You can only have a truly fully-reproducible build environment if you setup your toolchain to keep copies of every piece of external software so that you can do hermetic builds.

        I think this is a misguided way to workaround proper toolchain setup. Nix is pretty cool though.

        • @[email protected]English
          4•1 year ago

          That seems like an argument for maintaining a frozen repo of packages, not against containers.

          I am not arguing against containers, I am arguing that nix is more reproducible. Containers can be used with nix and are useful in other ways.

          an argument for maintaining a frozen repo of packages

          This is essentially what nix does. In addition it verifies that the packages are identical to the packages specified in your flake.nix file.

          You can only have a truly fully-reproducible build environment if you setup your toolchain to keep copies of every piece of external software so that you can do hermetic builds.

          This is essentially what Nix does, except Nix verifies the external software is the same with checksums. It also does hermetic builds.

          • nickwitha_k (he/him)English
            4•1 year ago

            Nix is indeed cool. I just see it as less practical than maintaining a toolchain for devs to use. Seems like reinventing the wheel, instead of airing-up the tires. I could well be absolutely wrong there - my experience is mainly enterprise software and not every process or tool there is used because it is the best one.

              • nickwitha_k (he/him)
                1•1 year ago

                I quite like the sound of Nix, every time I touch on it but haven’t really dug in yet. You’re making me really want to though.

            • @[email protected]English
              1•1 year ago

              I just see it as less practical than maintaining a toolchain for devs to use.

              There are definately some things preventing Nix adoption. What are the reasons you see it as less practical than the alternatives?

              What are alternative ways of maintaining a toolchain that achieves the same thing?

              • nickwitha_k (he/him)English
                2•1 year ago

                I see it as less practical mainly due to the extant tooling and age/maturity of the project.

                The ways that I’m most familiar with are use of software like Artifactory - basically a multi-repo. Using such a tool, any package or artifact can be readily retained for future use. Then, for builds, one only needs to ensure that it is used as the package source, regardless of type (PyPy, Docker image, binary, RPM, etc).

                Alternatively, one can use individual repos for any relevant package type but that’s a bit more overhead to manage.

      • @[email protected]English
        1•1 year ago

        I’ll certainly give this a read!

        Are you saying that nix will cache all the dependencies within itself/its “container,” or whatever its container replacement would be called?