Support extra packages in docker image

[jceb]

Is your feature request related to a problem?

I would like to build upon the docker.nix configuration provided in this repository directly from, instead of creating a Dockerfile. This worked well - I imported this repository as input and then imported and customized docker.nix with the supported variables.

However, I found that the extraPkgs parameter installs packages only in the root user's profile directory - /root/.nix-profile. This doesn't work for me, because I need to place a configuration file in /etc.

Proposed solution

I propose to add an additional parameter, e.g. extraBasePkgs that is appended to the contents parameter of pkgs.dockerTools.buildLayeredImageWithNixDb.

Alternative solutions

I tried to use .overrideAttrs on the output of pkgs.dockerTools.buildLayeredImageWithNixDb but failed. This might be an alternative.

Checklist

• checked latest Nix manual (source)
• checked open feature issues and pull requests for possible duplicates

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