Add Docker executor support for a Windows version

GitLab supports specific versions of Windows.

To add support for a new Windows version for the Docker executor, you must release a helper image with the same Windows version. Then you can run the helper image on the Windows host OS.

To build the helper image for the version, you need GitLab Runner installed on that Windows version, because Windows requires your host OS and container OS versions to match.

Infrastructure

We must build the helper image for it to be used for the user job.

Create a base image for infrastructure to use

To add support for a new Windows version, you might need to create a new helper image. Windows versions can run older helper images (backward compatibility), or might require a newly built helper image. For compatibility details, see Windows container version compatibility

The GitLab Runner helper image is built from a base image published by the runner-tools/base-images project. The windows target in dockerfiles/runner-helper/docker-bake.hcl defines the build configuration.

To support a new Windows version or architecture, that project must first publish the matching runner-helper:<version>-servercore-ltsc<year>[-<arch>] base image. For example, merge request 88 added the ltsc2025, ltsc2025-arm64, servercore, and nanoserver base images.

The windows-containers repository builds the GCP host VM images for the shared Windows runner fleet. The autoscaler provisions them.

For example, when adding support for Windows Server 2025, backward compatibility allowed reuse of the existing 2022 helper images. However, when adding support to Windows Server 2022, the Windows Server 2019 helper image was not compatible with process isolation, so a new image was required.

Some GCP base images require Docker installation during the build process. To update the CI/CD environment for a new image, update the following files:

  • .gitlab-ci.yml
  • .gitlab/ci/build.gitlab-ci.yml

Test the image generated

We recommend testing the image generated in the dev step. It is likely to be named dev xxx where xxx stands for the windows server version.

To test the image, the following steps can be followed:

  1. Add support for the new windows server version in GitLab Runner project and generate the gitlab-runner-helper.x86_64-windows.exe binary (or gitlab-runner-helper.arm64-windows.exe for ARM64 hosts).
  2. Create a VM using the disk image generated during the dev step. When adding support for windows server ltsc2022, the disk image name was runners-windows-21h1-core-containers-dev-40-mr
  3. Generate the gitlab-runner-helper Docker image from this VM. To do so, you need to download the gitlab-runner-helper.x86_64-windows.exe binary on the VM. As the Invoke-WebRequest PowerShell command might be unavailable, you should use the Start-BitsTransfer command instead.
  4. Create another VM using the new GCP windows server image to support.
  5. Install the gitlab-runner executable generated for the previously update GitLab-Runner project and register it to a project.
  6. Successfully launch a job.

An example of this procedure is summarized in this comment.

Publish the image

After we merge the merge request created from the previous step, we need to run the publish job manually for the image to be published to our production GCP project.

Take note of the image name that is created from the publish job, for example in this job we created an image called runners-windows-2019-core-containers-2020-07-17. This will be used for the install part.

Add two new runner managers

At this point we should have a base image ready in our production environment, so we can use it inside the CI pipeline for the GitLab Runner project. The only thing that is left is to set up the Runner Managers.

Register

Run gitlab-runner register to register the two new runners. These should be project-specific runners, so we need to use the registration token from the project settings. The name of the runner should follow the same naming convention as the existing ones.

For example, for Windows Server Core 2004 we should name the Runner Managers the following:

  1. windows-2004-private-runner-manager-1
  2. windows-2004-private-runner-manager-2

Once registered, make sure you safely store the runner tokens found in the config.toml file since we are going to need these for the installation step.

Finally, we’ll need to assign the new Runner Managers to the security fork project and to the ’liveness’ test support project. So for each of the new Runner Managers:

  1. Go to the Runners section of the Runner project CI/CD settings page;
  2. Unlock the new Runner by editing its properties and unchecking Lock to current projects;
  3. For the security fork project:
    1. Go to the Runners section of the project’s CI/CD settings page;
    2. Scroll down to the Other available runners section and enable the runner for this project;
  4. For the ’liveness’ test support project:
    1. Go to the Runners section of the project’s CI/CD settings page;
    2. Scroll down to the Other available runners section and enable the runner for this project;
  5. Lock the Runner back again in the Runner project CI/CD settings page.

Install

Install a new instance of autoscaler to have a specific config.toml for that Windows version. We need to update our Ansible repository (https://ops.gitlab.net/gitlab-com/gl-infra/ci-infrastructure-windows) to include the new Windows version.

For example, if we want to add support for Windows Server Core 2004 in the 13.7 milestone we can see this merge request: https://ops.gitlab.net/gitlab-com/gl-infra/ci-infrastructure-windows/-/merge_requests/70, where we update the following files:

  1. ansible/roles/runner/tasks/main.yml
  2. ansible/roles/runner/tasks/autoscaler.yml
  3. ansible/group_vars/gcp_role_runner_manager.yml
  4. ansible/host_vars/windows-shared-runners-manager-1.yml
  5. ansible/host_vars/windows-shared-runners-manager-2.yml

When opening a merge request make sure that the maintainer is aware that they need to register 2 new runners and save them inside the CI/CD variables with the keys defined in ansible/host_vars.

Publish registry.gitlab.com/gitlab-org/ci-cd/tests/liveness

The image registry.gitlab.com/gitlab-org/ci-cd/tests/liveness is used as part of the CI process for GitLab Runner. Make sure that an image based on the new Windows version is published.

For example, if we want to add support for Windows Server Core 2004 in the 13.7 milestone we can see the following merge request, where we update the following files:

  1. .gitlab-ci.yml
  2. Makefile

Update GitLab Runner to support specific Windows version

Since we need to provide a helper image for users to be able to use the Docker executor we have specific checks inside the code base, we need to allow the new Windows version.

We should update the following:

  1. Windows version detection: Add the kernel build number and version constant to supportedWindowsBuilds in helpers/container/windows/version.go, and update the surrounding tests.

  2. Version-to-image mapping: Add the version to the ltsc map in helpers/container/helperimage/windows_info.go, and update the surrounding tests. The image tag, prebuilt bundle name, and host architecture are all derived from this mapping.

  3. Helper image build: Add the new servercore:ltsc<year> entry (and, for a new architecture, the -arch variant) to the windows target in dockerfiles/runner-helper/docker-bake.hcl.

  4. Publish mapping: Map the built artifact to its published registry tag in scripts/pusher/helper-images.json.

  5. CI jobs: Add or update the following:

    • Prebuilt helper image job in .gitlab/ci/build.gitlab-ci.yml
    • WINDOWS_VERSION or WINDOWS_PREBUILT variables in .gitlab/ci/_common.gitlab-ci.yml (to run tests on the new version)
    • Test jobs in .gitlab/ci/test.gitlab-ci.yml and .gitlab/ci/coverage.gitlab-ci.yml
    • Quarantine file ci/.test-failures.servercore<version>.txt

  6. Documentation: Update the supported versions and helper image list in docs/executors/docker.md.

Example: Windows Server 2025 (LTSC2025) helper image support, including the arm64 variant, was implemented across several merge requests (parent issue 39182):

  • Merge request 88: Added the ltsc2025 and ltsc2025-arm64 base images (prerequisite in the runner-tools/base-images project).
  • Merge request 6033: Built servercore:ltsc2025 and servercore:ltsc2025-arm64 helper images from dockerfiles/runner-helper/docker-bake.hcl, scripts/pusher/helper-images.json, .gitlab/ci/build.gitlab-ci.yml base images. At this stage, the ARM64 image bundled the AMD64 helper binary under Windows emulation.
  • Merge request 6697: Added a native ARM64 gitlab-runner-helper.exe build target (Makefile.runner_helper.mk, ci/release_dir).
  • Merge request 6716: Bundled the native ARM64 helper binary into the servercore:ltsc2025-arm64 image instead of the emulated AMD64 binary (dockerfiles/runner-helper/docker-bake.hcl, scripts/pusher/helper-images.json).
  • Merge request 6717: Built nanoserver:ltsc2025 and nanoserver:ltsc2025-arm64 helper images.