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# This module deploys a NixOS host by building a system closure
# located at the specified attribute in the current repository.
#
# The closure's derivation path is persisted in the Terraform state to
# determine after Nix evaluation whether the system closure has
# changed and needs to be built/deployed.
#
# The system configuration is then built (or substituted) on the
# machine that runs `terraform apply`, then copied and activated on
# the target machine using `nix-copy-closure`.
variable "attrpath" {
description = "attribute set path pointing to the NixOS system closure"
type = string
}
variable "target_name" {
description = "unique name of the target machine"
type = string
}
variable "target_host" {
description = "address (IP or hostname) at which the target is reachable"
type = string
}
variable "entrypoint" {
description = <<EOT
Path to a .nix file (or directory containing `default.nix` file)
that provides the attrset specified in `closure`.
If unset, asks git for the root of the repository.
EOT
type = string
default = ""
}
variable "target_user" {
description = "username on the target machine"
type = string
}
variable "target_user_ssh_key" {
description = "SSH key to use for connecting to the target"
type = string
sensitive = true
}
# Fetch the derivation hash for the NixOS system.
data "external" "nixos_system" {
program = ["${path.module}/nixos-eval.sh"]
query = {
attrpath = var.attrpath
entrypoint = var.entrypoint
}
}
# Deploy the NixOS configuration if anything changed.
resource "null_resource" "nixos_deploy" {
connection {
type = "ssh"
host = var.target_host
user = var.target_user
private_key = var.target_user_ssh_key
}
# 1. Wait for SSH to become available.
provisioner "remote-exec" {
inline = ["true"]
}
# 2. Build NixOS system.
provisioner "local-exec" {
command = "nix-build ${data.external.nixos_system.result.drv} --no-out-link"
}
# 3. Copy closure to the target.
provisioner "local-exec" {
command = "${path.module}/nixos-copy.sh"
environment = {
SYSTEM_DRV = data.external.nixos_system.result.drv
TARGET_HOST = var.target_host
DEPLOY_KEY = var.target_user_ssh_key
TARGET_USER = var.target_user
}
}
# 4. Activate closure on the target.
provisioner "remote-exec" {
inline = [
"set -eu",
"SYSTEM=$(nix-build ${data.external.nixos_system.result.drv} --no-out-link)",
"sudo nix-env --profile /nix/var/nix/profiles/system --set $SYSTEM",
"sudo $SYSTEM/bin/switch-to-configuration switch",
]
}
triggers = {
nixos_drv = data.external.nixos_system.result.drv
attrpath = var.attrpath
target_host = var.target_host
target_name = var.target_name
}
}
output "nixos_drv" {
value = data.external.nixos_system.result
}
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