Create a docker image with service configuration included?

Help
1

I am playing around with containers and isolation of services, and I don’t really like the systemd containers due to them sharing the whole /nix

So, is it possible to somehow include the configutation in a docker image built with nix?

for example, an empy-basic docker image to run postfix would be something like:

{ pkgs ? import <nixpkgs> { config.packageOverrides = pkgs: { postfix = pkgs.postfix.override { withPgSQL = true; }; }; }
}:

pkgs.dockerTools.buildImage {
  name = "postfix";
  tag = "0.0.1";
  contents = [
    pkgs.postfix
    pkgs.pfixtools
  ];
  runAsRoot = ''
    #!${pkgs.stdenv.shell}
    ${pkgs.dockerTools.shadowSetup}
   # ...add user nobody and mail...
  '';
  config = {
    Cmd = [ "${pkgs.postfix}/bin/postfix" "start" ];
  };
}

But then I would have to mount volumes for the configuration.
I don’t mind mounting the configuration volumes instead of including the conf in the image, but how do I at least generate a conf that is not activated in my main system, so that I can maybe even have multiple instances of the same service with different confs?

2

IIUC, we want to populate your Docker image with Postfix configuration files which needs to be located in /etc. There are several ways to achieve this.

We can create files and directories with the extraCommands attribute, as used by a |Nginx example image](nixpkgs/examples.nix at 2be8dd990833dc07e338bc27489a211347bf94b9 · NixOS/nixpkgs · GitHub).

We could also use the contents attribute such as:

contents = [
  (pkgs.writeTextFile {
     name = "master.cf";
     destination = "/etc/postfix";
     text = "bla";
   })];
3

I was hoping more on the lines of reusing services.postfix that I can use in the system configuration.nix, but from your answer I gather that it is not possible.

It will be a bit more verbose, but I guess it’s ok for now, thank you