backport of commit 0f6561b (#24218)

Co-authored-by: James Rasell <[email protected]>

website/content/partials/virt-beta-callout.mdx

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+~> Beta Feature: The Virt task driver is in beta and under active development.
+Refer to the [repo README](https://github.com/hashicorp/nomad-driver-virt) for
+the latest updates. Do not use this driver in production environments.

website/content/plugins/drivers/virt/client.mdx

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+---
+layout: docs
+page_title: Client
+description: Nomad client requirements, capabilities, and configuration options for the Virt task driver.
+---
+
+# Client
+
+@include 'virt-beta-callout.mdx'
+
+The `virt` task driver is not built into Nomad. You must [downloaded][releases] onto the client
+host in the configured plugin directory. The client host must also be capable of running hardware
+accelerated KVM virtual machines, which you can check by using [kvm-ok][] command.
+Additional requirements:
+
+- Linux
+- Commands `bridge-utils`, `cloudinit`, `dnsmasq`, and `iptables`
+- [libvirt daemon][] installed and running
+- QEMU system packages installed
+- Nomad client running as root
+
+Use the following command to install the package requirements:
+
+```console
+$ sudo apt-get update && \
+  sudo apt-get install -y \
+  bridge-utils \
+  cloud-init \
+  dnsmasq \
+  iptables \
+  libvirt-daemon-system \
+  qemu-system \
+  qemu-system-x86 \
+  qemu-utils
+```
+
+## Client capabilities
+
+The `virt` task driver implements the following driver [capabilities][capabilities].
+
+| Feature              | Implementation |
+|----------------------|----------------|
+| `nomad alloc signal` | false          |
+| `nomad alloc exec`   | false          |
+| filesystem isolation | image          |
+| network isolation    | host           |
+| volume mounting      | false          |
+
+## Plugin configuration
+
+This example shows the default plugin configuration.
+
+```hcl
+plugin "nomad-driver-driver" {
+  config {
+    data_dir     = "/var/lib/virt"
+    image_paths  = ["/var/lib/virt", "${ALLOC_DIR}"]
+
+    emulator {
+      uri      = "qemu:///system"
+      user     = ""
+      password = ""
+    }
+  }
+}
+```
+
+- `data_dir` - (default: `"/var/lib/virt"`) - the directory for storing VM configuration files and
+  intermediate files.
+
+- `image_paths` - (default: `["/var/lib/virt", "${ALLOC_DIR}"]`) - an allow-list of paths the driver
+  is allowed to load an image from.
+
+- `emulator` - (block)
+  - `uri` - (default: `"qemu:///system"`) - The `uri` specifies which hypervisor to connect to.
+  - `user` - (default: `""`) - the username to use for authentication.
+  - `password` - (default: `""`) - the password to use for authentication.
+
+## Client attributes
+
+When installed, the `virt` plugin provides the following node attributes that you can use as
+constraints when authoring jobs.
+
+```
+driver.virt                              = true
+driver.virt.active                       = 0
+driver.virt.emulator.version             = 8002002
+driver.virt.inactive                     = 0bytes
+driver.virt.libvirt.version              = 10000000
+driver.virt.network.default.bridge_name  = virbr0
+driver.virt.network.default.state        = active
+```
+
+[releases]: https://releases.hashicorp.com/nomad-driver-virt
+[kvm-ok]: https://manpages.ubuntu.com/manpages/bionic/man1/kvm-ok.1.html
+[libvirt daemon]: https://libvirt.org/daemons.html
+[capabilities]: https://developer.hashicorp.com/nomad/docs/concepts/plugins/task-drivers#task-driver-plugin-api

website/content/plugins/drivers/virt/index.mdx

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+---
+layout: docs
+page_title: 'Drivers: virt'
+description: >-
+  The virt task driver leverages Linux capabilities and libvirt to run virtual
+  machines.
+---
+
+# Virt task driver
+
+@include 'virt-beta-callout.mdx'
+
+Name: `virt`
+
+The `virt` driver utilises the [libvirt][] API to run and manage virtual machines (VMs) via
+hypervisors such as [QEMU][]. It supports a wide variety of Nomad features including
+[workload identity][], [task templates][], and [service discovery][].
+
+
+[libvirt]: https://libvirt.org/
+[QEMU]: https://www.qemu.org/
+[workload identity]: https://developer.hashicorp.com/nomad/docs/concepts/workload-identity
+[task templates]: https://developer.hashicorp.com/nomad/docs/job-specification/template
+[service discovery]: https://developer.hashicorp.com/nomad/docs/networking/service-discovery
+[github]: https://github.com/hashicorp/nomad-driver-virt

website/content/plugins/drivers/virt/installation.mdx

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+---
+layout: docs
+page_title: Installation
+description: Installation of the virt task driver.
+---
+
+# Installation
+
+@include 'virt-beta-callout.mdx'
+
+Use the following instructions to download the task driver for use on your Nomad client host.
+
+<Tabs>
+  <Tab heading="Manual installation" group="manual">
+
+    Download a [precompiled binary](https://releases.hashicorp.com/nomad-driver-virt/) and
+    verify the binary using the available SHA-256 sums. Unzip the package. Make sure that the `nomad-driver-virt` binary is on your
+    [plugin_dir](/nomad/docs/configuration#plugin_dir) path, specified by the client's config file,
+    before continuing with the other guides.
+
+  </Tab>
+  <Tab heading="Ubuntu/Debian" group="manual">
+
+    Install the required packages.
+
+    ```shell-session
+    $ sudo apt-get update && \
+      sudo apt-get install wget gpg coreutils
+    ```
+
+    Add the HashiCorp [GPG key][gpg-key].
+
+    ```shell-session
+    $ wget -O- https://apt.releases.hashicorp.com/gpg | sudo gpg --dearmor -o /usr/share/keyrings/hashicorp-archive-keyring.gpg
+    ```
+
+    Add the official HashiCorp Linux test repository.
+
+    ```shell-session
+    $ echo "deb [signed-by=/usr/share/keyrings/hashicorp-archive-keyring.gpg] https://apt.releases.hashicorp.com $(lsb_release -cs) test" | sudo tee /etc/apt/sources.list.d/hashicorp.list
+    ```
+
+    Update and install.
+
+    ```shell-session
+    $ sudo apt-get update && sudo apt-get install nomad-driver-virt
+    ```
+
+  </Tab>
+  <Tab heading="CentOS/RHEL" group="linux">
+
+    Install `yum-config-manager` to manage your repositories.
+
+    ```shell-session
+    $ sudo yum install -y yum-utils
+    ```
+
+    Use `yum-config-manager` to add the official HashiCorp Linux repository.
+
+    ```shell-session
+    $ sudo yum-config-manager --add-repo https://rpm.releases.hashicorp.com/RHEL/hashicorp.repo
+    ```
+
+    Edit the repo file at `/etc/yum.repos.d/hashicorp.repo` and set `enabled=1` for `[hashicorp-test]`.
+
+    Install.
+
+    ```shell-session
+    $ sudo yum -y install nomad-driver-virt
+    ```
+
+  </Tab>
+</Tabs>

website/content/plugins/drivers/virt/task-config.mdx

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+---
+layout: docs
+page_title: Task Config
+description: Configure the virt task driver job specification parameters.
+---
+
+# Task configuration
+
+@include 'virt-beta-callout.mdx'
+
+Task configuration for an virt task includes setting an `image` to provide the base VM image as
+well as other parameters required for bootstrapping a VM instance.
+
+- `image` - (string: required) - Path to an `.img` cloud image to base the VM disk on. The image should
+  be located in an allowed path. The cloud image needs to include cloud-init, otherwise certain
+  task features are not available. You may also downloaded via the [artifact block][].
+
+- `use_thin_copy` - (bool: `false`) - Make a thin copy of the image using QEMU, and use it as the
+  backing cloud image for the VM.
+
+- `hostname` - (string: `"nomad-<task-name>"`) - The hostname to assign to the VM. As this value is
+  used as a network host name, it must be a valid DNS label according to RFC 1123. Nomad generates the default
+  value using the Nomad task name.
+
+- `cmds` - (list(string): optional) - List of commands to execute on the VM once it is running.
+  These commands can provide you with a quick way to start a process on the newly created
+  VM. When used in conjunction with the template, this command list can be a powerful start up tool.
+
+- `default_user_password` - (string: `""`) - Initial password for the default user
+  on the newly created VM. When set, the user must update the password on first connect.
+
+- `default_user_authorized_ssh_key` - (string: `""`) - SSH public key  added to the SSH
+  configuration for the default user of the cloud image distribution.
+
+- `user_data ` - (string: `""`) - Path to a cloud-init compliant user data file used as the user-data for the cloud-init configuration.
+
+- `primary_disk_size` - (int: required) - Disk space to assign to the VM. Must fit the VM's OS.
+
+Example:
+```hcl
+config {
+  image                           = "local/focal-server-cloudimg-amd64.img"
+  use_thing_copy                  = false
+  hostname                        = ""
+  cmds                            = ["python -m http.server 8000"]
+  #default_user_password          = "CHANGE-ME"
+  default_user_authorized_ssh_key = ""
+  user_data                       = ""
+  primary_disk_size               = 10000
+}
+```
+
+##### os
+
+The VM architecture and machine can be different from the client host. When this is the case, you must set the
+`os` block. By default, this information matches the client host where the driver
+plugin is running.
+
+- `arch` - (string: `""`) - The VM architecture.
+
+- `machine` - (string: `""`) - The machine type.
+
+Example:
+```hcl
+config {
+  os {
+    arch    = "x86_64"
+    machine = "pc-i440fx-2.9"
+  }
+}
+```
+
+##### network_interface
+
+You need to attach tasks to a libvirt network in order to access the internet and route
+from the local network. The `network_interface` block enables this as a list of network interfaces
+that the driver should attach to the VM. This feature only supports a single entry.
+
+- `bridge` - (block) - Attach the VM to a bridge network. `virbr0`, the default libvirt
+  network, is a bridge network.
+
+  - `name` - The name of the bridge interface to use. This relates to the output from commands
+  such as `virsh net-info`.
+
+  - `ports` - A list of port labels to expose on the host via mapping to the network
+  interface. These labels must exist within the job specification [network block][].
+
+Example:
+```hcl
+config {
+  network_interface {
+    bridge {
+      name  = "virbr0"
+      ports = ["ssh", "http"]
+    }
+  }
+}
+```
+
+### Full example
+
+The following job specification displays use of all the configuration options, as well as other
+blocks that are useful when deploying tasks via the virt driver. You need to modify parameters, such as the
+`default_user_authorized_ssh_key`, before use depending on your
+requirements and Nomad setup.
+
+```hcl
+job "virt-example" {
+
+  group "virt-group" {
+
+    network {
+      mode     = "host"
+      provider = "nomad"
+      port "ssh" {
+        to = 22
+      }
+    }
+
+    task "virt-task" {
+
+      driver = "nomad-driver-virt"
+
+      artifact {
+        source      = "http://cloud-images.ubuntu.com/focal/current/focal-server-cloudimg-amd64.img"
+        destination = "local/focal-server-cloudimg-amd64.img"
+        mode        = "file"
+      }
+
+      config {
+        image                           = "local/focal-server-cloudimg-amd64.img"
+        primary_disk_size               = 26000
+        #default_user_password          = "CHANGE-ME"
+        default_user_authorized_ssh_key = "ssh-ed25519 AAAAC3NzaC1lZDI..."
+
+        network_interface {
+          bridge {
+            name  = "virbr0"
+            ports = ["ssh"]
+          }
+        }
+      }
+
+      resources {
+        cores  = 2
+        memory = 4096
+      }
+    }
+  }
+}
+
+```
+
+[artifact block]: https://developer.hashicorp.com/nomad/docs/job-specification/artifact
+[network block]: https://developer.hashicorp.com/nomad/docs/job-specification/network

website/data/docs-nav-data.json

@@ -1989,6 +1989,27 @@
         "title": "Raw Fork/Exec",
         "path": "drivers/raw_exec"
       },
+      {
+        "title": "Virt <sup>Beta</sup>",
+        "routes": [
+          {
+            "title": "Overview",
+            "href": "/plugins/drivers/virt"
+          },
+          {
+            "title": "Installation",
+            "href": "/plugins/drivers/virt/installation"
+          },
+          {
+            "title": "Client",
+            "href": "/plugins/drivers/virt/client"
+          },
+          {
+            "title": "Task Config",
+            "href": "/plugins/drivers/virt/task-config"
+          }
+        ]
+      },
       {
         "title": "Community",
         "routes": [