---
layout: docs
page_title: 'Drivers: LXC'
sidebar_title: LXC
description: The LXC task driver is used to run application containers using LXC.
---

# LXC Driver

Name: `lxc`

The `lxc` driver provides an interface for using LXC for running application
containers. You can download the external LXC driver [here][lxc-driver]. For more detailed instructions on how to set up and use this driver, please refer to the [LXC guide][lxc-guide].

~> **Note:** The LXC client set up has changed in Nomad 0.9. You must use the new [plugin syntax][plugin] and install the external LXC driver in the [plugin_dir][plugin_dir] prior to upgrading. See [plugin options][plugin-options] below for an example. Note the job specification remains the same.

## Task Configuration

```hcl
task "busybox" {
  driver = "lxc"

  config {
    log_level = "trace"
    verbosity = "verbose"
    template = "/usr/share/lxc/templates/lxc-busybox"
    template_args = []

    # these optional values can be set in the template
    distro =          ""
    release =         ""
    arch =            ""
    image_variant =   "default"
    image_server =    "images.linuxcontainers.org"
    gpg_key_id =      ""
    gpg_key_server =  ""
    disable_gpg =     false
    flush_cache =     false
    force_cache =     false
  }
}
```

The `lxc` driver supports the following configuration in the job spec:

- `template` - The LXC template to run.

  ```hcl
  config {
    template = "/usr/share/lxc/templates/lxc-alpine"
  }
  ```

- `template_args` - A list of argument strings to pass into the template.

- `log_level` - (Optional) LXC library's logging level. Defaults to `error`.
  Must be one of `trace`, `debug`, `info`, `warn`, or `error`.

  ```hcl
  config {
    log_level = "debug"
  }
  ```

- `verbosity` - (Optional) Enables extra verbosity in the LXC library's
  logging. Defaults to `quiet`. Must be one of `quiet` or `verbose`.

  ```hcl
  config {
    verbosity = "quiet"
  }
  ```

- `volumes` - (Optional) A list of `host_path:container_path` strings to bind-mount host paths to container paths. Mounting host paths outside of the allocation directory can be disabled on clients by setting the [`volumes_enabled`](#volumes_enabled) option set to false. This will limit volumes to directories that exist inside the allocation directory.

  ~> **Note:** Unlike the similar option for the docker driver, this
  option must not have an absolute path as the `container_path`
  component. This will cause an error when submitting a job.

  Setting this does not affect the standard bind-mounts of `alloc`,
  `local`, and `secrets`, which are always created.

  ```hcl
  config {
    volumes = [
      # Use absolute paths to mount arbitrary paths on the host
      "/path/on/host:path/in/container",

      # Use relative paths to rebind paths already in the allocation dir
      "relative/to/task:also/in/container"
    ]
  }
  ```

- `release` - (Optional) The name/version of the distribution. By default this is set by the template.

- `arch` - (Optional) The architecture of the container. By default this is set by the template.

- `image_server` - (Optional) The hostname of the image server. Defaults to `images.linuxcontainers.org`.

- `image_variant` - (Optional) The variant of the image. Defaults to `default` or as set by the template.

- `disable_gpg` - (Optional) Disable GPG validation of images. Defaults to `false`, and enabling this flag is not recommended.

- `flush_cache` - (Optional) Flush the local copy of the image (if present) and force it to be fetched from the image server. Defaults to `false`.

- `force_cache` - (Optional) Force the use of the local copy even if expired. Defaults to `false`.

- `gpg_key_server`: GPG key server used for checking image signatures. Default is set by the underlying LXC library.

- `gpg_key_id`: GPG key ID used for checking image signatures. Default is set by the underlying LXC library.

## Networking

Currently the `lxc` driver only supports host networking. See the `none`
networking type in the `lxc.container.conf` [manual][lxc_man] for more
information.

## Client Requirements

The `lxc` driver requires the following:

- 64-bit Linux host
- The `linux_amd64` Nomad binary
- The LXC driver binary placed in the [plugin_dir][plugin_dir] directory.
- `liblxc` to be installed
- `lxc-templates` to be installed

## Plugin Options

- `enabled` - The `lxc` driver may be disabled on hosts by setting this option to `false` (defaults to `true`).

- `volumes_enabled`<a id="volumes_enabled"></a> - Specifies whether host can bind-mount host paths to container paths (defaults to `true`).

- `lxc_path` - The location in which all containers are stored (commonly defaults to `/var/lib/lxc`). See [`lxc-create`][lxc-create] for more details.

- `gc` stanza:
  - `container` - Defaults to `true`. This option can be used to disable Nomad
    from removing a container when the task exits. Under a name conflict,
    Nomad may still remove the dead container.

An example of using these plugin options with the new [plugin
syntax][plugin] is shown below:

```hcl
plugin "nomad-driver-lxc" {
  config {
    enabled = true
    volumes_enabled = true
    lxc_path = "/var/lib/lxc"
    gc {
      container = false
    }
  }
}
```

Please note the plugin name should match whatever name you have specified for the external driver in the [plugin_dir][plugin_dir] directory.

## Client Configuration

-> Only use this section for pre-0.9 releases of Nomad. If you are using Nomad
0.9 or above, please see [plugin options][plugin-options]

The `lxc` driver has the following [client-level options][client_options]:

- `lxc.enable` - The `lxc` driver may be disabled on hosts by setting this
  option to `false` (defaults to `true`).

## Client Attributes

The `lxc` driver will set the following client attributes:

- `driver.lxc` - Set to `1` if LXC is found and enabled on the host node.
- `driver.lxc.version` - Version of `lxc` e.g.: `1.1.0`.

## Resource Isolation

This driver supports CPU and memory isolation via the `lxc` library. Network
isolation is not supported as of now.

[lxc-create]: https://linuxcontainers.org/lxc/manpages/man1/lxc-create.1.html
[lxc-driver]: https://releases.hashicorp.com/nomad-driver-lxc
[lxc-guide]: /guides/operating-a-job/external/lxc.html
[lxc_man]: https://linuxcontainers.org/lxc/manpages/man5/lxc.container.conf.5.html#lbAM
[plugin]: /docs/configuration/plugin
[plugin_dir]: /docs/configuration#plugin_dir
[plugin-options]: #plugin-options
[client_options]: /docs/configuration/client#options