this post was submitted on 21 Jul 2023
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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.

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[–] astral_avocado 17 points 1 year ago (39 children)

I wish he had written why he's so anti-container/docker. That's a pretty unusual stance I haven't been exposed to yet.

[–] [email protected] 16 points 1 year ago (29 children)

Hi!

First I'd like to clarify that I'm not "anti-container/Docker". 😅

There is a lot of discussion on this article (with my comments!) going on over at Tildes. I don't wanna copy-paste everything from there, but I'll share the first main response I gave to someone who had very similar feedback to kick-start some discussion on those points here as well:

Some high level points on the "why":

  • Reproducibility: Docker builds are not reproducible, and especially in a company with more than a handful of developers, it's nice not to have to worry about a docker build command in the on-boarding docs failing inexplicably (from the POV of the regular joe developer) from one day to the next

  • Cost: Docker licenses for most companies now cost $9/user/month (minimum of 5 seats required) - this is very steep for something that doesn't guarantee reproducibility and has poor performance to boot (see below)

  • Performance: Docker performance on macOS (and Windows), especially storage mount performance remains poor; this is even more acutely felt when working with languages like Node where the dependencies are file-count heavy. Sure, you could just issue everyone Linux laptops, but these days hiring is hard enough without shooting yourself in the foot by not providing a recent MBP to new devs by default

I think it's also worth drawing a line between containers as a local development tool and containers as a deployment artifact, as the above points don't really apply to the latter.

[–] CodeBlooded 8 points 1 year ago (13 children)

Docker builds are not reproducible

What makes you say that?

My team relies on Docker because it is reproducible…

[–] uthredii 4 points 1 year ago* (last edited 1 year ago) (2 children)

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.

[–] [email protected] 10 points 1 year ago (1 children)

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.

[–] uthredii 4 points 1 year ago* (last edited 1 year ago) (1 children)

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.

[–] [email protected] 4 points 1 year ago (2 children)

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.

[–] uthredii 2 points 1 year ago (1 children)

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?

[–] [email protected] 2 points 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] 2 points 1 year ago (1 children)

@nickwitha_k @uthredii I’d like to think a better analogy would be that nix is like using a 3D model of a wheel instead of a compass and a straightedge to make wheels hehe 🙃

[–] [email protected] 1 points 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.

[–] CodeBlooded 2 points 1 year ago (1 children)

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?

[–] uthredii 1 points 1 year ago

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

Yep, sort of.

It saves each version of your dependencies to the /nix/store folder with a checksum prefixing the program name. For example you might have the following Firefox programs

/nix/store/l7ih0zcw2csi880kfcq37lnl295r44pj-firefox-100.0.2
/nix/store/cm1bdi4hp8g8ic5jxqjhzmm7gl3a6c46-firefox-108.0.1
/nix/store/rfr0n62z21ymi0ljj04qw2d7fgy2ckrq-firefox-114.0.1

Because of this you can largely avoid dependency conflicts. For example a program A could depend on /nix/store/cm1bdi4hp8g8ic5jxqjhzmm7gl3a6c46-firefox-108.0.1 and a program B could depend on /nix/store/rfr0n62z21ymi0ljj04qw2d7fgy2ckrq-firefox-114.0.1 and both programs would work as both have dependencies satisfied. AFAIK using other build systems you would have to break program A or program B (or find versions of program A and program B where both dependencies are satisfied).

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