open-nomad/website/source/docs/drivers/rkt.html.md

---
layout: "docs"
page_title: "Drivers: Rkt"
sidebar_current: "docs-drivers-rkt"
description: |-
  The rkt task driver is used to run application containers using rkt.
---

# Rkt Driver

Name: `rkt`

The `rkt` driver provides an interface for using CoreOS rkt for running
application containers.

## Task Configuration

```hcl
task "webservice" {
  driver = "rkt"

  config {
    image = "redis:3.2"
  }
}
```

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

* `image` - The image to run. May be specified by name, hash, ACI address
  or docker registry.

    ```hcl
    config {
      image = "https://hub.docker.internal/redis:3.2"
    }
    ```

* `command` - (Optional) A command to execute on the ACI.

    ```hcl
    config {
      command = "my-command"
    }
    ```

* `args` - (Optional) A list of arguments to the optional `command`. References
  to environment variables or any [interpretable Nomad
  variables](/docs/runtime/interpolation.html) will be interpreted before
  launching the task.

    ```hcl
    config {
      args = [
        "-bind", "${NOMAD_PORT_http}",
        "${nomad.datacenter}",
        "${MY_ENV}",
        "${meta.foo}",
      ]
    }
    ```

* `trust_prefix` - (Optional) The trust prefix to be passed to rkt. Must be
  reachable from the box running the nomad agent. If not specified, the image is
  run without verifying the image signature.

* `dns_servers` - (Optional) A list of DNS servers to be used in the container.
  Alternatively a list containing just `host` or `none`. `host` uses the host's
  `resolv.conf` while `none` forces use of the image's name resolution configuration.

* `dns_search_domains` - (Optional) A list of DNS search domains to be used in
   the containers.

* `net` - (Optional) A list of networks to be used by the containers

* `port_map` - (Optional) A key/value map of ports used by the container. The
   value is the port name specified in the image manifest file.  When running
   Docker images with rkt the port names will be of the form `${PORT}-tcp`. See
   [networking](#networking) below for more details.

   ```hcl
    port_map {
            # If running a Docker image that exposes port 8080
            app = "8080-tcp"
    }
   ```
   

* `debug` - (Optional) Enable rkt command debug option.

* `no_overlay` - (Optional) When enabled, will use --no-overlay=true flag for 'rkt run'.
  Useful when running jobs on older systems affected by https://github.com/rkt/rkt/issues/1922

* `volumes` - (Optional) A list of `host_path:container_path` strings to bind
  host paths to container paths.

    ```hcl
    config {
      volumes = ["/path/on/host:/path/in/container"]
    }
    ```

## Networking

The `rkt` can specify `--net` and `--port` for the rkt client. Hence, there are two ways to use host ports by
using `--net=host` or `--port=PORT` with your network.

Example:

```
task "redis" {
	# Use rkt to run the task.
	driver = "rkt"

	config {
		# Use docker image with port defined
		image = "docker://redis:latest"
		port_map {
			app = "6379-tcp"
		}
	}

	service {
		port = "app"
	}

	resources {
		network {
			mbits = 10
			port "app" {
			    static = 12345
			}
		}
	}
}
```

### Allocating Ports

You can allocate ports to your task using the port syntax described on the
[networking page](/docs/job-specification/network.html).

When you use port allocation, the image manifest needs to declare public ports and host has configured network.
For more information, please refer to [rkt Networking](https://coreos.com/rkt/docs/latest/networking/overview.html).

## Client Requirements

The `rkt` driver requires rkt to be installed and in your system's `$PATH`.
The `trust_prefix` must be accessible by the node running Nomad. This can be an
internal source, private to your cluster, but it must be reachable by the client
over HTTP.

## Client Configuration

The `rkt` driver has the following [client configuration
options](/docs/agent/configuration/client.html#options):

* `rkt.volumes.enabled`: Defaults to `true`. Allows tasks to bind host paths
  (`volumes`) inside their container. Binding relative paths is always allowed
  and will be resolved relative to the allocation's directory.


## Client Attributes

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

* `driver.rkt` - Set to `1` if rkt is found on the host node. Nomad determines
  this by executing `rkt version` on the host and parsing the output
* `driver.rkt.version` - Version of `rkt` eg: `1.1.0`. Note that the minimum required
  version is `1.0.0`
* `driver.rkt.appc.version` - Version of `appc` that `rkt` is using eg: `1.1.0`

Here is an example of using these properties in a job file:

```hcl
job "docs" {
  # Only run this job where the rkt version is higher than 0.8.
  constraint {
    attribute = "${driver.rkt.version}"
    operator  = ">"
    value     = "1.2"
  }
}
```

## Resource Isolation

This driver supports CPU and memory isolation by delegating to `rkt`. Network
isolation is not supported as of now.