Configure the QEMU task driver

Name: qemu

The qemu driver provides a generic virtual machine runner. QEMU can utilize the KVM kernel module to utilize hardware virtualization features and provide great performance. Currently the qemu driver can map a set of ports from the host machine to the guest virtual machine, and provides configuration for resource allocation.

The qemu driver can execute any regular qemu image (e.g. qcow, img, iso), and is currently invoked with qemu-system-x86_64.

The driver requires the image to be accessible from the Nomad client via the artifact downloader.

Capabilities

The qemu driver implements the following capabilities.

Feature	Implementation
`nomad alloc signal`	false
`nomad alloc exec`	false
filesystem isolation	image
network isolation	none
volume mounting	none

Client Requirements

The qemu driver requires QEMU to be installed and in your system's $PATH. The task must also specify at least one artifact to download, as this is the only way to retrieve the image being run.

Client Attributes

The qemu driver will set the following client attributes:

driver.qemu - Set to 1 if QEMU is found on the host node. Nomad determines this by executing qemu-system-x86_64 -version on the host and parsing the output
driver.qemu.version - Version of qemu-system-x86_64, ex: 2.4.0

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

job "docs" {
  # Only run this job where the qemu version is higher than 1.2.3.
  constraint {
    attribute = "${driver.qemu.version}"
    operator  = ">"
    value     = "1.2.3"
  }
}

Plugin Options

plugin "qemu" {
  config {
    image_paths    = ["/mnt/image/paths"]
    args_allowlist = ["-drive", "-usbdevice"]
  }
}

image_paths ([]string: []) - Specifies the host paths the QEMU driver is allowed to load images from.
args_allowlist ([]string: []) - Specifies the command line flags that the args option is permitted to pass to QEMU. If unset, a job submitter can pass any command line flag into QEMU, including flags that provide the VM with access to host devices such as USB drives. Refer to the QEMU documentation for the available flags.

Resource Isolation

Nomad uses QEMU to provide full software virtualization for virtual machine workloads. Nomad can use QEMU KVM's hardware-assisted virtualization to deliver better performance.

Virtualization provides the highest level of isolation for workloads that require additional security, and resource use is constrained by the QEMU hypervisor rather than the host kernel. VM network traffic still flows through the host's interface(s).

Note that the strong isolation provided by virtualization only applies to the workload once the VM is started. Operators should use the args_allowlist option to prevent job submitters from accessing devices and resources they are not allowed to access.

Next steps

Use the Java task driver in a job.