Troubles understanding how to strip unused dependencies from docker images

[dukeofcool199]

Howdy Haskell Flake Peoples,

at this time, i am trying to build a website using hakyll and servant. I have successfully gotten it setup and am able to build docker images with it.

Recently I added tailwindcss to my project using the tailwind package on hackage. After adding this dependency, my docker images have grown quite a lot because now it includes the tailwind cli, and nodejs as a part of the package closure.

I have tried adding the settings options like JustStaticExecutables, and tried adding the package to the removeReferencesTo list.
I have even tried overriding postInstall build steps on the derivation directly (this just threw a nix error, and this might be showing my lack of knowledge of nix based haskell environments) all to no avail.

Would someone be willing to help guide me on how to remove un-needed dependencies correctly? If so I would really appreciate it.

At this time the code I'm working on is proprietary, if someone needs a reproducible build to help me solve this problem, ask and I will try to make a repo that is close enough to the original to suffice.

Hope everyone is have a great day :)

[peterbecich]

I see JustStaticExecutables is both setting option and a function: https://community.flake.parts/haskell-flake/size
Have you tried:

...
contents = [
  pkgs.haskell.lib.justStaticExecutables self'.packages.my-package
  ...
  ]

This worked for my case.

[dukeofcool199]

thank you @peterbecich for the very timely response.

shortly after writing up this question. I realized what my actual question is. And it has to do with the way executables are built within a cabal project.

here is a snippet from my cabal file

executable site-builder
    import:           warnings
    main-is:          Site.hs
    build-depends:    base,hakyll,tailwind,data-default,monad-logger,text,directory,filepath
    hs-source-dirs:   src/Site/
    other-modules: SiteConfig
    default-language: Haskell2010


executable server
    import:           warnings
    main-is:          Server.hs
    build-depends:    base,servant,servant-server,warp,wai-extra,directory,optparse-applicative
    hs-source-dirs:   src/Server/
    other-modules: Options
    default-language: Haskell2010

as seen here, I have two outputs being built when i build the project with nix build and tailwind is a valid runtime dependency of the site-builder output.

the way I use this, I use site-builder to build the static assets. I then output those assets into a derivation, which I bundle together with the server output to be served by servant. Which then I put into a docker container.

What I see now is that when I include the cabal project one of the contents of the image definition, it includes site-builder alongside server.

so I guess my real question is, is there a way to have haskell-flake, only build out one of these outputs (namely server)? that way I can only include server and it's closure, along with the prebuild website assets into my docker image.

[dukeofcool199]

I conceded, and eventually decided to just break up my modules into multiple cabal projects with a cabal.project file in the root of my project. I wanted to see if it was possible to break things up while only having a single cabal project. If this is possible, I would still like some guidance. If this is generally a bad idea it would be nice to know why that is the case as well. I am still very new to the world of Haskell.

[peterbecich]

That's unnecessary to split up the project. You specify the executable by

config = {
           Cmd = [ "executable-name" ];

config goes alongside contents.

The Docker image will contain multiple executables but only one will be the entry point.