Nomad Systemd-Nspawn driver

This is a task driver for Hashicorp Nomad to run containers with systemd-nspawn.

Containers started via this driver will have private networking enabled by default and their machine ID will be set to the allocation ID of the started Nomad task.

Client requirements

• Nomad 1.4.0+ running as root
• Go 1.20
• Linux
• systemd-nspawn installed

Building the driver from source

Checkout this repository and simply run make.

$ git clone https://github.com/JanMa/nomad-driver-nspawn.git
$ cd nomad-driver-nspawn
$ make

Testing the driver

To execute the built-in test suite run

$ make test

Using the driver

To test the driver, run the Nomad agent in development mode with the following command

$ sudo nomad agent -dev -plugin-dir=$(pwd) -config=example/config.hcl

Minimal job example

    task "debian" {
      driver = "nspawn"
      config {
        image = "example/Debian/image"
        resolv_conf = "copy-host"
      }
    }

Argument reference

The driver supports the following subset of possible arguments from systemd-nspawn, which should cover a broad range of use cases:

• boot - (Optional) true (default) or false. Search for an init program and invoke it as PID 1. Arguments specified in command will be used as arguments for the init program.

• ephemeral - (Optional) true or false (default). Make an ephemeral copy of the image before staring the container.

• process_two - (Optional) true or false (default). Start the command specified with command as PID 2, using a minimal stub init as PID 1.

• read_only - (Optional) true or false (default). Mount the used image as read only.

• user_namespacing - (Optional) true (default) or false. Enable user namespacing features inside the container.

• private_users - (Optional). Controls how user namespacing is enabled. For this option to take effect, user_namespacing needs to be set to true.

• private_users_ownership - (Optional). Controls how to adjust the container image's UIDs and GIDs to match the UID/GID range chosen with private_users. For this option to take effect, user_namespacing needs to be set to true.

• command - (Optional) A list of strings to pass as the used command to the container.

  config {
    command = [ "/bin/bash", "-c", "dhclient && nginx && tail -f /var/log/nginx/access.log" ]
  }

• console - (Optional) Configures how to set up standard input, output and error output for the container.

• image - The image to be used in the container. This can either be the path to a directory, the path to a file system image or block device or the name of an image registered with systemd-machined. A path can be specified as a relative path from the configured Nomad plugin directory. This option is mandatory.

• image_download - (Optional) Download the used image according to the settings defined in this block. Structure is documented below.

• pivot_root - (Optional) Pivot the specified directory to be the containers root directory.

• resolv_conf - (Optional) Configure how /etc/resolv.conf is handled inside the container.

• user - (Optional) Change to the specified user in the container's user database.

• volatile - (Optional) Boot the container in volatile mode.

• working_directory - (Optional) Set the working directory inside the container.

• bind - (Optional) Files or directories to bind mount inside the container.

  config {
    bind {
      "/var/lib/postgresql" = "/postgres"
    }
  }

• bind_read_only - (Optional) Files or directories to bind mount read only inside the container.

  config {
    bind_read_only {
      "/etc/passwd" = "/etc/passwd"
    }
  }
  

• environment - (Optional) Environment variables to pass to the init process in the container.

  config {
    environment = {
      FOO = "bar"
    }
  }

• port_map - (Optional) DEPRECATED A key-value map of port labels. Works the same way as in the docker driver. Note: systemd-nspawn will not expose ports to the loopback interface of your host.

  config {
    port_map {
      http = 80
    }
  }

• ports - (Optional) A list of port labels. Works the same way as in the docker driver. Note: systemd-nspawn will not expose ports to the loopback interface of your host.

  config {
    ports = ["http"]
  }

• capability - (Optional) List of additional capabilities to grant the container.

  config {
    capability = ["CAP_NET_ADMIN"]
  }

• network_veth - (Optional) true (default) or false. Create a virtual ethernet link between the host and the container.

• network_bridge - (Optional) Attach the virtual container interface to a host side bridge that must already exist.

• network_zone - (Optional) Start the container in the given network zone. Each container may only be part of one zone, but each zone may contain any number of containers.

The image_download block supports the following arguments:

• url - The URL of the image to download. The URL must be of type http://, https:// or a valid docker image reference. This option is mandatory.
• verify - (Optional) no (default), signature or checksum. Whether to verify the image before making it available. This option has no effect when downloading docker images.
• force - (Optional) true or false (default) If a local copy already exists, delete it first and replace it by the newly downloaded image.
• type - (Optional) tar (default), raw or docker. The type of image to download.

Networking

The nspawn driver has support for host networking and also bridge mode networking. It can therefore be used with Consul service mesh.

Plugin Options

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

• volumes - Enable support for Volumes in the driver (defaults to true).

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

plugin "nspawn" {
  config {
    enabled = true
    volumes = true
  }
}

Client Attributes

The nspawn driver will set the following client attributes:

• driver.nspawn - Set to true if systemd-nspawn is found and enabled on the host node and Nomad is running with root privileges.

• driver.nspawn.version - Version of systemd-nspawn e.g.: 244.