Add tutorial for deploying NixOS with Terraform

source/conf.py

@@ -371,6 +371,15 @@
 # If false, no index is generated.
 #epub_use_index = True
 
+# it's an SPA
+linkcheck_ignore = [r'https://app.terraform.io']
+
+# Anchors are not present in HTML
+linkcheck_anchors_ignore = [
+    r"instance_type",
+    r"authentication"
+]
+
 
 # Example configuration for intersphinx: refer to the Python standard library.
 intersphinx_mapping = {}

source/tutorials/deploying-nixos-using-terraform.rst

@@ -0,0 +1,179 @@
+.. _deploying-nixos-using-terraform:
+
+Deploying NixOS using Terraform
+===============================
+
+Assuming you're `familiar with the basics of Terraform <https://www.terraform.io/intro/index.html>`_,
+by the end of tutorial you will have provisioned Amazon AWS instance with Terraform
+and use Nix to deploy incremental changes to NixOS running on the instance. 
+
+We'll look at how to boot a NixOS machine and how to deploy the incremental changes:
+
+
+Booting NixOS image
+-------------------
+
+1. Start by providing terraform executable:
+
+.. code:: shell
+
+   nix-shell -p terraform
+
+2. We are using `Terraform Cloud <https://app.terraform.io>`_ as a `state/locking backend <https://www.terraform.io/docs/state/purpose.html>`_:
+
+.. code:: shell
+
+   terraform login
+
+3. Make sure to `create an organization <https://app.terraform.io/app/organizations/new>`_ like ``myorganization`` in your Terraform Cloud account.
+
+4. Inside ``myorganization`` `create a workspace <https://app.terraform.io/app/cachix/workspaces/new>`_ by chosing 
+"CLI-driven workflow and pick name like  ``myapp``.
+
+4. Inside a new directory create ``main.tf`` file with the following contents that will start an AWS instance with NixOS image using one SSH keypair and an SSH security group:
+
+.. code:: 
+
+    terraform {
+        backend "remote" {
+            organization = "myorganization"
+
+            workspaces {
+                name = "myapp"
+            }
+        }
+    }
+
+    provider "aws" {
+        region = "eu-central-1"
+    }
+
+    module "nixos_image" {
+        source  = "git::https://github.com/tweag/terraform-nixos.git//aws_image_nixos?ref=5f5a0408b299874d6a29d1271e9bffeee4c9ca71"
+        release = "20.09"
+    }
+
+    resource "aws_security_group" "ssh_and_egress" {
+        ingress {
+            from_port   = 22
+            to_port     = 22
+            protocol    = "tcp"
+            cidr_blocks = [ "0.0.0.0/0" ]
+        }
+
+        egress {
+            from_port       = 0
+            to_port         = 0
+            protocol        = "-1"
+            cidr_blocks     = ["0.0.0.0/0"]
+        }
+    }
+
+    resource "tls_private_key" "state_ssh_key" {
+        algorithm = "RSA"
+    }
+
+    resource "local_file" "machine_ssh_key" {
+        sensitive_content = tls_private_key.state_ssh_key.private_key_pem
+        filename          = "${path.module}/id_rsa.pem"
+        file_permission   = "0600"
+    }
+
+    resource "aws_key_pair" "generated_key" {
+        key_name   = "generated-key-${sha256(tls_private_key.state_ssh_key.public_key_openssh)}"
+        public_key = tls_private_key.state_ssh_key.public_key_openssh
+    }
+
+    resource "aws_instance" "machine" {
+        ami             = module.nixos_image.ami
+        instance_type   = "t3.micro"
+        security_groups = [ aws_security_group.ssh_and_egress.name ]
+        key_name        = aws_key_pair.generated_key.key_name
+
+        root_block_device {
+            volume_size = 50 # GiB
+        }
+    }
+
+    output "public_dns" {
+        value = aws_instance.machine.public_dns
+    }
+
+The only NixOS specific snippet is:
+
+.. code:: 
+
+   module "nixos_image" {
+     source = "git::https://github.com/tweag/terraform-nixos.git/aws_image_nixos?ref=5f5a0408b299874d6a29d1271e9bffeee4c9ca71"
+     release = "20.09"
+   }
+
+.. note::
+
+   ``aws_image_nixos`` module will return an NixOS AMI given `NixOS release number <https://status.nixos.org>`_
+   so that ``aws_instance`` resource can reference the AMI in `instance_type <https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/instance#instance_type>`_ argument.
+
+5. Make sure to `configure AWS credentials <https://registry.terraform.io/providers/hashicorp/aws/latest/docs#authentication>`_.
+
+6. Applying Terraform configuration should get you a running NixOS:
+
+.. code:: shell
+
+   terraform init
+   terraform apply
+
+
+Deploying NixOS changes
+-----------------------
+
+Once AWS instance is running an NixOS image via Terraform, we can teach Terraform to always build
+latest NixOS configuration and apply those changes to your instance.
+
+1. Create ``configuration.nix`` with the following contents:
+
+.. code:: nix 
+
+    { config, lib, pkgs, ... }: {
+      imports = [ <nixpkgs/nixos/modules/virtualisation/amazon-image.nix> ];
+
+      # Open https://search.nixos.org/options for all options
+    }
+
+2. Append the following snippet to your ``main.tf``:
+
+.. code:: 
+
+    module "deploy_nixos" {
+        source = "git::https://github.com/tweag/terraform-nixos.git//deploy_nixos?ref=5f5a0408b299874d6a29d1271e9bffeee4c9ca71"
+        nixos_config = "${path.module}/configuration.nix"
+        target_host = aws_instance.machine.public_ip
+        ssh_private_key_file = local_file.machine_ssh_key.filename
+        ssh_agent = false
+    }
+
+3. Deploy:
+
+.. code:: shell
+
+   terraform init
+   terraform apply
+
+
+Caveats
+-------
+
+- ``deploy_nixos`` module requires NixOS to be installed on the target machine and Nix on the host machine.
+
+- ``deploy_nixos`` module doesn't work when the client and target architectures are different (unless you use `distributed builds <https://nixos.org/manual/nix/unstable/advanced-topics/distributed-builds.html>`_).
+
+- If you need to inject a value into Nix, there is no elegant solution.
+
+- Each machine is evaluated separately, so note that your memory requirements will grow linearly with the number of machine.
+
+
+Going Forward
+-------------
+
+- It's possible to `switch to use Google Compute Engine provider <https://github.com/tweag/terraform-nixos/tree/master/google_image_nixos#readme>`_.
+
+- `deploy_nixos module <https://github.com/tweag/terraform-nixos/tree/master/deploy_nixos#readme>`_ supports a number arguments, for example to upload keys, etc.

source/tutorials/index.rst

@@ -11,4 +11,5 @@ Tutorials
    continuous-integration-github-actions.rst
    dev-environment.rst
    building-and-running-docker-images.rst
+   deploying-nixos-using-terraform.rst
    contributing.rst

source/tutorials/install-nix.rst

@@ -4,7 +4,7 @@ Install Nix
 ===========
 
 Install Nix on **any Linux distribution**, **MacOS** and **Windows (via WSL)**
-via the recommended `multi-user installation <https://nixos.org/nix/manual/#chap-installation>`_:
+via the recommended `multi-user installation <https://nixos.org/manual/nix/stable/#chap-installation>`_:
 
 .. code:: bash