hi, I am trying to deploy custom nixos image that is created with nixos-generators for digitalocean.
the machine boots, /etc/nixos/configuration.nix looks like this by default:

{ config, lib, pkgs, modulesPath, ... }:
{
  imports = lib.optional (builtins.pathExists ./do-userdata.nix) ./do-userdata.nix ++ [
    (modulesPath + "/virtualisation/digital-ocean-config.nix")
  ];

even if I add
environment.systemPackages = with pkgs; [ cowsay ];
and rebuild, it doesn't seem to install the required package.
Any idea what I should look into?

an option is useful if you are going to override the value when you call the module
for a shared variable, here is what I do with my authorized ssh keys for example.

# ssh.nix
{
  keys = [ "pubKey1" "pubKey2"]; 
}

And you import the keys in your config :
users.users.root.openssh.authorizedKeys.keys = (import ./relative-path/to/ssh.nix).keys;

an option is useful if you are going to override the value when you call the module
for a shared variable, here is what I do with my authorized ssh keys for example.

# ssh.nix
{
  keys = [ "pubKey1" "pubKey2" ]; 
}

And you import the keys in your config :
users.users.root.openssh.authorizedKeys.keys = (import ./relative-path/to/ssh.nix).keys;