Rkt Driver

Nomad 0.11 converted the rkt driver to an external driver. We will not prioritize features or pull requests that affect the rkt driver. The external driver is available as an open source repository for community ownership.

Name: rkt

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

Task Configuration

task "webservice" {
  driver = "rkt"

  config {
    image = "redis:7"
  }
}

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.

  config {
    image = "https://hub.docker.internal/redis:7"
  }
  

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

  config {
    command = "my-command"
  }
  

• args - (Optional) A list of arguments to the optional command. References to environment variables or any interpretable Nomad variables will be interpreted before launching the task.

  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 with --insecure-options=all.

• insecure_options - (Optional) List of insecure options for rkt. Consult rkt --help for list of supported values. This list overrides the --insecure-options=all default when no trust_prefix is provided in the job config, which can be effectively used to enforce secure runs, using insecure_options = ["none"] option.

  config {
    image = "example.com/image:1.0"
    insecure_options = ["image", "tls", "ondisk"]
  }
  

• 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 below for more details.

  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[:readOnly] strings to bind host paths to container paths. Mount is done read-write by default; an optional third parameter readOnly can be provided to make it read-only.

  config {
    volumes = ["/path/on/host:/path/in/container", "/readonly/path/on/host:/path/in/container:readOnly"]
  }
  

• group - (Optional) Specifies the group that will run the task. Sets the --group flag and overrides the group specified by the image. The user may be specified at the task level.

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 {
            port "app" {
              static = 12345
            }
        }
    }
}

Allocating Ports

You can allocate ports to your task using the port syntax described on the networking page.

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.

Client Requirements

The rkt driver requires the following:

• The Nomad client agent to be running as the root user.
• 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.

Plugin Options

• 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 Configuration

The rkt driver has the following client configuration 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 e.g.: 1.27.0. Note that the minimum required version is 1.27.0
• driver.rkt.appc.version - Version of appc that rkt is using e.g.: 1.1.0

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

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.