Configuring OpenTofu

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In this section, we’ll walk through the steps to configure OpenTofu to manage a NixOS virtual machine on a Proxmox server, from setting up permissions to writing and applying your infrastructure definitions.

Prerequisites

Proxmox: Ensure you have a Proxmox server set up and accessible.
OpenTofu: Install OpenTofu on your local machine. You can follow the installation guide for detailed instructions.
NixOS ISO: Download the latest minimal NixOS ISO image and upload it to your Proxmox server. See this guide for instructions on how to upload the ISO.

Configuration

Before starting to write OpenTofu configuration, we need to set up a couple of things in Proxmox to allow OpenTofu to manage your Proxmox resources.

Create the Proxmox user, role and token for OpenTofu

To allow OpenTofu to manage your Proxmox resources, you need to create a user and assign it the necessary permissions. Follow these steps:

Log in to your Proxmox web interface.
Navigate to Datacenter > Node > Shell.

Run the following commands to create a new user and assign it a role:

pveum role add TerraformProv -privs "Datastore.AllocateSpace Datastore.AllocateTemplate Datastore.Audit Pool.Allocate Sys.Audit Sys.Console Sys.Modify VM.Allocate VM.Audit VM.Clone VM.Config.CDROM VM.Config.Cloudinit VM.Config.CPU VM.Config.Disk VM.Config.HWType VM.Config.Memory VM.Config.Network VM.Config.Options VM.Migrate VM.Monitor VM.PowerMgmt SDN.Use"
pveum user add terraform-prov@pve --password <password>
pveum aclmod / -user terraform-prov@pve -role TerraformProv

Create a token for the terraform-prov@pve user:

Navigate to Datacenter > Permissions > API Tokens and click on Add.

Select the previously created user, assign a name to the token (e.g., tofu), and uncheck Privilege Separation. You may optionally set an expiration date and add a comment.

You will receive a token ID and a secret. Save these securely, as you will need them for your OpenTofu configuration.

Create a NixOS VM

To simplify the process of managing the NixOS VM, we will first create a basic NixOS VM using the Proxmox web interface. This VM will serve as a template for our OpenTofu configuration.

In the Proxmox web interface, on the top right corner, click on Create VM.

Fill in the following details (you can adjust as needed) and leave the rest as default:

Tab	Setting	Value	Notes
General	Name	`nixos-vm`	Set a name for the VM
OS	ISO Image	NixOS ISO	Select the NixOS ISO you uploaded earlier
System	Qemu Agent	✓ Selected	Enable Qemu Agent
System	Machine	`q35`	Modern chipset with PCIe support
Disks	Disk Size	`128G`	Set the disk size
CPU	Cores	`4`	Set the number of CPU cores
Memory	Memory (MiB)	`6144`	Set the memory size
Network	Model	`VirtIO`	Use VirtIO for better performance

You should see a summary of your VM configuration like this:

Proxmox Create VM Summary

Click on Finish to create the VM.

Write configuration files

Now that we have the Proxmox user, role, and token set up, and a basic NixOS VM created, we can write the OpenTofu configuration files.

Create a directory for your OpenTofu configuration files, e.g., opentofu, and create the following files:
- Directoryopentofu
  - imports.tf // File to import existing Proxmox VM
  - opentofu.auto.tfvars // File containing secrets
  - providers.tf // File to configure the Proxmox provider
  - variables.tf // File to define OpenTofu variables

To interact with Proxmox using OpenTofu, you need to set up the Proxmox provider. Update the file named providers.tf with the following content:

terraform {
  required_providers {
    proxmox = {
      source  = "Telmate/proxmox"
      version = "3.0.2-rc03"
    }
  }
}

provider "proxmox" {
  # Configuration options

}

Run the following command to download the Proxmox provider:

 tofu init

Expected output:

Initializing the backend...

Initializing provider plugins...

- Finding telmate/proxmox versions matching "3.0.1-rc8"...
- Installing telmate/proxmox v3.0.1-rc8...
- Installed telmate/proxmox v3.0.1-rc8. Signature validation was skipped due to the registry not containing GPG keys for this provider

OpenTofu has created a lock file .terraform.lock.hcl to record the provider
selections it made above. Include this file in your version control repository
so that OpenTofu can guarantee to make the same selections by default when
you run "tofu init" in the future.

OpenTofu has been successfully initialized!

You may now begin working with OpenTofu. Try running "tofu plan" to see
any changes that are required for your infrastructure. All OpenTofu commands
should now work.

If you ever set or change modules or backend configuration for OpenTofu,
rerun this command to reinitialize your working directory. If you forget, other
commands will detect it and remind you to do so if necessary.

You should now have a .terraform directory and a .terraform.lock.hcl file in your opentofu directory.

Next, create a file named imports.tf to import the existing NixOS VM into OpenTofu:

import {
 to = proxmox_vm_qemu.nixos
 id = "pve1/qemu/105" // Replace with your Proxmox node and VM ID
}

Create a file named variables.tf to define the variables used in your OpenTofu configuration:

 variable "pm_api_url" {
   type        = string
   description = "The Proxmox server URL (https://ip:port/api2/json)"
 }

 variable "pm_api_token_id" {
   type        = string
   description = "The Proxmox API Token ID (user@realm!tokenid)"
 }

 variable "pm_api_token_secret" {
   type        = string
   sensitive   = true
   description = "The Proxmox API Token secret (UUID)"
 }

Create a file named opentofu.auto.tfvars to store your Proxmox API credentials:

 pm_api_url = "https://<proxmox-ip>:8006/api2/json"
 pm_api_token_id = "terraform-prov@pve!tofu" // Replace with your Proxmox API Token ID
 pm_api_token_secret = "<your-token-secret>" // Replace with your Proxmox API Token secret

Update the providers.tf file to use the variables defined in variables.tf:

 terraform {
   required_providers {
     proxmox = {
       source  = "Telmate/proxmox"
       version = "3.0.1-rc8"
     }
   }
 }

 provider "proxmox" {
   # Configuration options
   pm_api_url          = var.pm_api_url
   pm_api_token_id     = var.pm_api_token_id
   pm_api_token_secret = var.pm_api_token_secret
   pm_tls_insecure     = true
 }

Run the following command to generate the OpenTofu configuration:

tofu plan -generate-config-out=nixos.tf

It’s possible that you will get errors related to the VM configuration. You can ignore these errors for now, as we will fix them in the next step.

  proxmox_vm_qemu.nixos: Preparing import... [id=pve1/qemu/105]
  proxmox_vm_qemu.nixos: Refreshing state... [id=pve1/qemu/105]

  Planning failed. OpenTofu encountered an error while generating this plan.

  ╷
  │ Warning: Config generation is experimental
  │
  │ Generating configuration during import is currently experimental, and the generated configuration format may change in future versions.
  ╵
  ╷
  │ Error: Conflicting configuration arguments
  │
  │   with proxmox_vm_qemu.nixos,
  │   on nixos.tf line 78:
  │   (source code not available)
  │
  │ "disks.0.ide.0.ide2.0.cdrom.0.iso": conflicts with disks.0.ide.0.ide2.0.cdrom.0.passthrough
  ╵
  ╷
  │ Error: Conflicting configuration arguments
  │
  │   with proxmox_vm_qemu.nixos,
  │   on nixos.tf line 79:
  │   (source code not available)
  │
  │ "disks.0.ide.0.ide2.0.cdrom.0.passthrough": conflicts with disks.0.ide.0.ide2.0.cdrom.0.iso
  ╵

Open the generated nixos.tf file and fix the configuration errors. You can remove the conflicting lines or adjust them as needed. For example, you can remove the passthrough lines block:

resource "proxmox_vm_qemu" "nixos" {
  # Other configurations...

  disks {
    ide {
      # Remove the conflicting lines
      cdrom {
        iso = "local:iso/nixos-minimal-24.11.718051.9b5ac7ad4529-x86_64-linux.iso"
        passthrough = false
      }
    }
  }

  # Other configurations...
}

After fixing the configuration errors, run the following commands to plan again, format the configuration, and apply the changes:

tofu plan

Expected output:

  proxmox_vm_qemu.nixos: Preparing import... [id=pve1/qemu/105]
  proxmox_vm_qemu.nixos: Refreshing state... [id=pve1/qemu/105]

  OpenTofu used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
    ~ update in-place

  OpenTofu will perform the following actions:

    # proxmox_vm_qemu.nixos will be updated in-place
    # (imported from "pve1/qemu/105")
    ~ resource "proxmox_vm_qemu" "nixos" {
       # Resources...
      }

  Plan: 1 to import, 0 to add, 1 to change, 0 to destroy.

  ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

  Note: You didn't use the -out option to save this plan, so OpenTofu can't guarantee to take exactly these actions if you run "tofu apply" now.

Now format the configuration file to ensure it follows best practices, is easy to read, and apply the changes:

 tofu fmt
 tofu apply -auto-approve

Expected output:

 proxmox_vm_qemu.nixos: Preparing import... [id=pve1/qemu/105]
 proxmox_vm_qemu.nixos: Refreshing state... [id=pve1/qemu/105]

 # Other output...

 Plan: 0 to add, 1 to change, 0 to destroy.
 proxmox_vm_qemu.nixos: Modifying... [id=pve1/qemu/105]
 proxmox_vm_qemu.nixos: Modifications complete after 2s [id=pve1/qemu/105]

 Apply complete! Resources: 0 added, 1 changed, 0 destroyed.

You can start the NixOS VM using either of the following methods:
- Manual
- Automatic
- Through the Proxmox web interface: Navigate to your VM and click the “Start” button
- Via command line: qm start 105
- By adding onboot = true to the VM configuration in the nixos.tf file (see below)
resource "proxmox_vm_qemu" "nixos" { # ... other configuration ... onboot = true # ... rest of configuration ... }
After adding onboot = true, run tofu apply to update the VM configuration. The VM will then automatically start whenever the Proxmox host system boots up.
Your project structure should now look like this:
- Directoryopentofu
  - Directory.terraform/
    …
  - .terraform.lock.hcl
  - imports.tf
  - nixos.tf
  - opentofu.auto.tfvars
  - providers.tf
  - terraform.tfstate
  - terraform.tfstate.backup
  - variables.tf

You have now successfully set up OpenTofu to manage a NixOS VM on Proxmox. You can now use OpenTofu to automate the management of your Proxmox resources, making it easier to deploy and maintain your NixOS VMs.

References