QEMU for Docker

QEMU in a docker container using KVM acceleration.

Features

• Multi-platform
• KVM acceleration

Usage

Via docker-compose.yml

version: "3"
services:
    qemu:
        container_name: qemu
        image: qemux/qemu-docker:latest
        environment:
            DISK_SIZE: "16G"
            BOOT: "https://dl-cdn.alpinelinux.org/alpine/v3.18/releases/x86_64/alpine-standard-3.18.2-x86_64.iso"
        devices:
            - /dev/kvm
        cap_add:
            - NET_ADMIN                       
        ports:
            - 22:22
        restart: on-failure

Via docker run

docker run -it --rm -e "BOOT=http://www.example.com/image.iso" --device=/dev/kvm --cap-add NET_ADMIN qemux/qemu-docker:latest

FAQ

• How do I specify the boot disk?

  You can modify the BOOT environment variable to specify the URL of an ISO image:

  environment:
      BOOT: "https://dl-cdn.alpinelinux.org/alpine/v3.18/releases/x86_64/alpine-standard-3.18.2-x86_64.iso"

  It will be downloaded only once, during the initial run of the container.

• How do I change the size of the data disk?

  To expand the default size of 16 GB, locate the DISK_SIZE setting in your compose file and modify it to your preferred capacity:

  environment:
      DISK_SIZE: "256G"

  This can also be used to resize the existing disk to a larger capacity without data loss.

• How do I change the location of the data disk?

  To change the data disk's location from the default Docker volume, include the following bind mount in your compose file:

  volumes:
      - /home/user/data:/storage

  Replace the example path /home/user/data with the desired storage folder.

• How do I increase the amount of CPU or RAM?

  By default, a single core and 512 MB of RAM are allocated to the container. To increase this, add the following environment variables:

  environment:
      CPU_CORES: "4"
      RAM_SIZE: "2048M"

• How do I verify if my system supports KVM?

  To verify if your system supports KVM, run the following commands:

  sudo apt install cpu-checker
  sudo kvm-ok

  If you receive an error from kvm-ok indicating that KVM acceleration can't be used, check your BIOS settings.

• How do I provide extra arguments to QEMU?

  You can create the ARGUMENTS environment variable to provide additional arguments to QEMU at runtime:

  environment:
      ARGUMENTS: "-drive file=/seed.iso,format=raw,if=virtio"

• How do I assign an individual IP address to the container?

  By default, the container uses bridge networking, which shares the IP address with the host.

  If you want to assign an individual IP address to the container, you can create a macvlan network as follows:

  docker network create -d macvlan \
      --subnet=192.168.0.0/24 \
      --gateway=192.168.0.1 \
      --ip-range=192.168.0.100/28 \
      -o parent=eth0 vlan

  Be sure to modify these values to match your local subnet.

  Once you have created the network, change your compose file to look as follows:

  services:
      qemu:
          container_name: qemu
          ..<snip>..
          networks:
              vlan:             
                  ipv4_address: 192.168.0.100
  
  networks:
      vlan:
          external: true

  An added benefit of this approach is that you won't have to perform any port mapping anymore since all ports will be exposed by default.

  Please note that this IP address won't be accessible from the Docker host due to the design of macvlan, which doesn't permit communication between the two. If this is a concern, you need to create a second macvlan as a workaround.

• How can the container acquire an IP address from my router?

  After configuring the container for macvlan (see above), it is possible for the VM to become part of your home network by requesting an IP from your router, just like your other devices.

  To enable this feature, add the following lines to your compose file:

  environment:
      DHCP: "Y"
  devices:
      - /dev/vhost-net
  device_cgroup_rules:
      - 'c *:* rwm'

  Please note that even if you don't need DHCP, it's still recommended to enable this feature as it prevents NAT issues and increases performance by using a macvtap interface.