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Merge pull request #110 from nix-dot-dev/tutorial-terraform
Add tutorial for deploying NixOS with Terraform
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.. _deploying-nixos-using-terraform: | ||
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Deploying NixOS using Terraform | ||
=============================== | ||
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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. | ||
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We'll look at how to boot a NixOS machine and how to deploy the incremental changes: | ||
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Booting NixOS image | ||
------------------- | ||
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1. Start by providing terraform executable: | ||
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.. 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>`_: | ||
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.. 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. | ||
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4. Inside ``myorganization`` `create a workspace <https://app.terraform.io/app/cachix/workspaces/new>`_ by chosing | ||
"CLI-driven workflow and pick name like ``myapp``. | ||
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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: | ||
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.. 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: | ||
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.. code:: | ||
module "nixos_image" { | ||
source = "git::https://github.com/tweag/terraform-nixos.git/aws_image_nixos?ref=5f5a0408b299874d6a29d1271e9bffeee4c9ca71" | ||
release = "20.09" | ||
} | ||
.. note:: | ||
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``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. | ||
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5. Make sure to `configure AWS credentials <https://registry.terraform.io/providers/hashicorp/aws/latest/docs#authentication>`_. | ||
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6. Applying Terraform configuration should get you a running NixOS: | ||
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.. code:: shell | ||
terraform init | ||
terraform apply | ||
Deploying NixOS changes | ||
----------------------- | ||
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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. | ||
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1. Create ``configuration.nix`` with the following contents: | ||
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.. 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``: | ||
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.. 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: | ||
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.. code:: shell | ||
terraform init | ||
terraform apply | ||
Caveats | ||
------- | ||
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- ``deploy_nixos`` module requires NixOS to be installed on the target machine and Nix on the host machine. | ||
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- ``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>`_). | ||
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- If you need to inject a value into Nix, there is no elegant solution. | ||
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- Each machine is evaluated separately, so note that your memory requirements will grow linearly with the number of machine. | ||
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Going Forward | ||
------------- | ||
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- It's possible to `switch to use Google Compute Engine provider <https://github.com/tweag/terraform-nixos/tree/master/google_image_nixos#readme>`_. | ||
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- `deploy_nixos module <https://github.com/tweag/terraform-nixos/tree/master/deploy_nixos#readme>`_ supports a number arguments, for example to upload keys, etc. |
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