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

---
layout: "docs"
page_title: "Drivers: Qemu"
sidebar_current: "docs-drivers-qemu"
description: |-
  The Qemu task driver is used to run virtual machines using Qemu/KVM.
---

# Qemu 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`.

## Task Configuration

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

* `artifact_source` - **(Required)** The hosted location of the source Qemu image. Must be accessible
  from the Nomad client, via HTTP.
* `checksum` - **(Optional)** The checksum type and value for the `artifact_source` image.
  The format is `type:value`, where type is any of `md5`, `sha1`, `sha256`, or `sha512`,
  and the value is the computed checksum. If a checksum is supplied and does not
  match the downloaded artifact, the driver will fail to start
* `accelerator` - (Optional) The type of accelerator to use in the invocation.
  If the host machine has `Qemu` installed with KVM support, users can specify
  `kvm` for the `accelerator`. Default is `tcg`
* `port_map` - **(Optional)** A `map[string]int` that maps port labels to ports
  on the guest. This forwards the host port to the guest vm. For example,
  `port_map { db = 6539 }` would forward the host port with label `db` to the
  guest vm's port 6539.

## Client Requirements

The `Qemu` driver requires Qemu to be installed and in your system's `$PATH`.
The `artifact_source` 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 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`

## 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).