How to setup Gitlab runner with KVM enabled

To implement the CI pipeline for the Android project, I need to run Gitlab CI, in which KVM is enabled.

TL; TR

1. Enable VTx virtualization technology in your server BIOS
2. Pass /dev/kvm to Gitlab runner

Sample .gitlab-ci.yml

Test - E2E:
  stage: Testing
  image: reactnativecommunity/react-native-android:latest
  before_script:
    - apt update && apt install -y cpu-checker && apt auto-remove
    - kvm-ok
    - npm i -g envinfo detox-cli && envinfo
    # Increase file watcher limit, see more here: https://github.com/guard/listen/wiki/Increasing-the-amount-of-inotify-watchers#the-technical-details
    - echo fs.inotify.max_user_watches=524288 | tee -a /etc/sysctl.conf && sysctl -p
    - mkdir -p /root/.android && touch /root/.android/repositories.cfg
    - echo yes | $ANDROID_HOME/cmdline-tools/latest/bin/sdkmanager --channel=0 --verbose "system-images;android-28;default;x86_64"    
    - echo no | $ANDROID_HOME/cmdline-tools/latest/bin/avdmanager --verbose create avd --force --name "Pixel_API_28" --device "Pixel_API_28_AOSP" -d pixel --package 'system-images;android-28;default;x86_64'

However, the pipeline was failing with the following error.

$ kvm-ok
INFO: /dev/kvm does not exist
HINT:   sudo modprobe kvm_intel
/usr/sbin/kvm-ok: 89: modprobe: not found

Enable VTx virtualization technology

First, I had to configure my server to enable VTx Virtualization Technology. To enable VTx, I followed the below steps.

1. Turn off/on the server
2. Access to BIOS (In my case, F10)
3. Go to Security -> System Security
4. Enable Virtualization technology (VTx)
5. Click F10 to accept the change
6. Save the change and hard power off and power it back on

Once you reboot the server, make sure you run kvm-ok to confirm the KVM virtualization is enabled.

Update Gitlab runner

Now, to allow Gitlab runner to use KVM, I made some changes on my docker-compose.yml for Gitlab runner.

services:
  ... other services ...
  gitlab-runner-1:
    container_name: gitlab-runner-1
    image: gitlab/gitlab-runner:latest
    restart: unless-stopped
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
      - /dev/kvm:/dev/kvm

  gitlab-runner-1-register:
    container_name: gitlab-runner-1-register
    image: gitlab/gitlab-runner:latest
    restart: "no"
    volumes:
      - gitlab_runner_1_config:/etc/gitlab-runner
      - /var/run/docker.sock:/var/run/docker.sock
    depends_on:
      - gitlab-runner-1
    command: >
      register
        ... other parameters ...
        --docker-devices=/dev/kvm
        --docker-volumes=/var/run/docker.sock:/var/run/docker.sock

volumes:
  gitlab_runner_1_config:

Or if you are using config.toml

concurrent = 1
check_interval = 0

[session_server]
  session_timeout = 1800

[[runners]]
  name = "docker-runner-1"
  url = "<url>"
  token = "<token>"
  executor = "docker"
  [runners.docker]
    tls_verify = false
    image = "docker:stable"
    privileged = true
    disable_entrypoint_overwrite = false
    oom_kill_disable = false
    disable_cache = false
    devices = ["/dev/kvm"]
    volumes = ["/var/run/docker.sock","/cache"]
    shm_size = 0

Note that make sure you deregister existing runners from Gitlab before adding new runners with /dev/kvm.

And Voila!

Once you restart the CI pipeline, the kvm-ok will show the result as below:

$ kvm-ok
INFO: /dev/kvm exists
KVM acceleration can be used