Consider Terranix Integration

[scottbot95]

This would probably be better as a discussion, but discussions weren't enabled on this repo at time of creation

Overview

Terranix is "a NixOS way to create terraform json files." It leverages the NixOS module system to generate a terraform config file.

By providing the utilities in this package as terranix module(s) in addition to (or instead of) the base terraform module, we could potentially simplify the implementation and provide a more flexible interface for consumers of this module.

Pros

• NixOS modules are far more flexible than Terraform modules, allowing overriding of values created by the modules.
• Tighter coupling to the Nix language simplifies implementation of deploy_nix (I believe the nix-instantiate.sh script could be removed entirely as all that info could be computed directly in the nix expression)

Cons

• Must continue to maintain the terraform HCL version of the module to allow non-terranix users to consume the module.
• Duplicating logic between the Terranix and HCL versions leads to substantially increased maintenance cost and significantly increase the chance for bugs to be introduced.
• Resources/data/etc created by Terranix modules are not namespaced like with native Terraform modules. This could potentially cause naming collisions

[betaboon]

heya. just wanted to let you know that I'm already using terraform-nixos + terranix for quite a while. that was the initial reason for this terranix PR

here's the snippet of my flake.nix that's relevant:

{
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
    flake-utils.url = "github:numtide/flake-utils";
    terranix = {
      url = "github:terranix/terranix";
      inputs.nixpkgs.follows = "nixpkgs";
      inputs.flake-utils.follows = "flake-utils";
    };
    terraform-nixos = {
      url = "github:tweag/terraform-nixos";
      flake = false;
    };
  };

  outputs = inputs@{ self, ... }:
    let

      inherit (inputs.nixpkgs.lib) nixosSystem;
      inherit (inputs.flake-utils.lib) eachDefaultSystem;
      inherit (inputs.terranix.lib) terranixConfiguration;

    in
    {

      nixosConfigurations.myhost = nixosSystem {
        system = "x86_64-linux";
        specialArgs = { inherit inputs; };
        modules = [
          ./myhost.nix
        ];
      };

      terraformConfigurations.mydeployment = terranixConfiguration {
        system = "x86_64-linux";
        extraArgs = { inherit inputs; };
        modules = [
          ./mydeployment.nix
        ];
      };

    } // (eachDefaultSystem (system:
      let pkgs = import inputs.nixpkgs { inherit system; }; in
      {

        apps.deploy = {
          type = "app";
          program = toString (pkgs.writers.writeBash "deploy" ''
            set -e
            PATH=$PATH:"${pkgs.terraform}/bin"
            WORKSPACE=$(terraform workspace show)
            OUT_LINK=./config.tf.json
            [ -e $OUT_LINK ] && rm -f $OUT_LINK
            nix build --out-link $OUT_LINK .#terraformConfigurations.$WORKSPACE
            terraform init
            terraform apply $@
          '');
        };
      }));
}

and mydeployment.nix:

{ config, pkgs, lib, inputs, ... }:
{

  module."nixos_deploy_myhost" = {
    source = "${inputs.terraform-nixos}/deploy_nixos";
    target_user = "username";
    target_host = "hostname";
    target_port = 2222;
    ssh_agent = true;
    flake = true;
    nixos_config = "myhost";
  };

}