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Continuous integration and continuous deployment (CI/CD) pipelines have become a crucial part of modern software development, allowing developers to build, test, and deploy code changes quickly and efficiently. By automating the process of building and deploying applications, CI/CD pipelines can help teams improve code quality, reduce errors, and speed up the time-to-market for new features and applications.

GitLab Runners are the applications that process CI/CD jobs on GitLab.com and self-hosted GitLab instances. GitLab.com provides their own hosted runners that are shared amongst users of the site, but you can also set up dedicated private runners for your projects through several different installation types. For enterprises or individuals that like to manage their own pipeline infrastructure in the cloud, the GitLab Runner Operator, available as a Red Hat Certified Operator in OpenShift, provides a fast and easy cloud-native installation of GitLab Runners.

As a way to showcase the simplicity and functionality of the GitLab Runner Operator, I thought it would be fun to also highlight some exciting developments in Fedora Linux and use the GitLab Runner Operator to build customized base images for Fedora Silverblue.

Fedora Silverblue is a cutting-edge immutable distribution of Fedora Linux. Recently, its hybrid image and package management system rpm-ostree has gained the ability to boot from OCI containers. This allows users or enterprises to build their own customized base images with the familiar workflow of Dockerfiles and Containerfiles.

In the following tutorial, we will set up a fully automated build system for our Fedora Silverblue images using the GitLab Runner Operator.


You will need a few previously configured and installed resources that we will not be covering in the tutorial:

  • An OpenShift cluster
  • An existing Fedora Silverblue installation (if you want to actually use the custom images)
  • A GitLab.com account

Installing and Configuring the GitLab Runner Operator

Open the Operators heading in the sidebar of your OpenShift cluster and click on OperatorHub. Search for the GitLab Runner operator and click the Certified option (the Community version of the operator is also available but this tutorial will stick to the Certified on OpenShift variant). Before clicking Install, note the Prerequisites section of the operator’s description. The GitLab Runner Operator requires you first install cert-manager:

oc apply -f https://github.com/cert-manager/cert-manager/releases/download/v1.7.1/cert-manager.yaml

After doing so, click Install to install the GitLab Runner Operator.

On the next screen you will be prompted to change any of the default installation options. If you need or want to scope to a specific namespace do so now, otherwise continue with the default options. I also suggest leaving Update approval set to Automatic since that's one key benefit of using an operator.

Allow the installation a moment to finish up and then navigate to your Installed Operators and then the GitLab Runner Operator. Here you will see the same info text from earlier, as well as a link under Provided APIs where you can create a Runner instance. In the info text below are instructions for linking your Runners to your GitLab repositories, which we will follow now.

Creating and registering our Runner instance

1. Creating the registration token Secret

First, we must create a Secret with a registration token from GitLab which our new Runner will use to register with our repository. Open GitLab.com or your private GitLab instance and then open the repository you want to register. Navigate to Settings and then CI/CD. Expand the section titled Runners and then look to the section Project runners. This is where we will find our registration token and the URL you will use to register your Runner instance.

Also note the Shared runners section if you're using GitLab.com. These are public runners provided by GitLab.com. Disable shared runners for this project since we will be using our own private runners.

Create your Secret, inserting your repository's registration token into the runner-registration-token field. You can do this in the web console or through the terminal interface. I created a file named gitlab-runner-secret.yml and then added it to my cluster:

apiVersion: v1
kind: Secret
name: gitlab-runner-secret
type: Opaque
runner-registration-token: YOUR_TOKEN_HERE
oc apply -f gitlab-runner-secret.yml

2. Configuring the runner with a ConfigMap

Before we create our runner, we also need to create a ConfigMap with some customization options. GitLab Runners can normally be configured with a config.toml file. In a Kubernetes context we can add those customizations with a ConfigMap that contains our config.toml file.

Since we are running our build containers in the environment of an OpenShift cluster, we need to be sure the build containers run without escalated privileges and as a non-root user (Note: there are ways around this if you really know you need a privileged build environment, but we will be sticking with a non-root setup). Here's a simple config.toml that specifies the runner pod will run as non-root user 1000:

name = "gitlab-runner"
url = "https://gitlab.com"
executor = "kubernetes"
run_as_non_root = true
run_as_user = 1000

To add this to our cluster as a ConfigMap:

oc create configmap my-runner-config --from-file=config.toml

3. Starting the Runner instance

Now we can create our actual Runner instance. Again, you can do this with the web console by clicking Create instance on the GitLab Runner Operator page, or through the terminal. Either way, we want to be sure that our Custom Resource Definition includes the correct GitLab URL, the name of our registration token Secret, the name of our ConfigMap, and that it includes "openshift" in the tags (this last item of the "openshift" tag is required for jobs to be passed to your cluster). Here is a basic CRD named gitlab-runner.yml which fulfills all our criteria:

apiVersion: apps.gitlab.com/v1beta2
kind: Runner
name: gitlab-runner
gitlabUrl: https://gitlab.com
token: gitlab-runner-secret
tags: openshift
config: my-runner-config

To install to our cluster:

oc apply -f gitlab-runner.yml

You can now check the status of your new runner in the web console or through the terminal with oc get runners. We should also check in our GitLab project's CI/CD settings to make sure the runner properly linked to our repository. You should now see a runner under the heading Assigned project runners with the same name as the CRD we created and installed.

Using our Runner to Build Silverblue Images

1. Defining the GitLab CI/CD pipeline jobs

Now that our runner is installed, configured, and linked to our project, we can the write the GitLab CI file that will define our image build. GitLab provides many examples of their gitlab-ci.yml file structure for different project types. We will be writing our own, utilizing buildah to build our Silverblue images.

The gitlab-ci.yml we will use looks as follows:

- build

stage: build
- openshift
image: quay.io/buildah/stable
- export HOME=/tmp
- buildah login --username "$CI_REGISTRY_USER" --password "$CI_REGISTRY_PASSWORD" "$CI_REGISTRY"
- buildah build -t "$CI_REGISTRY_IMAGE:latest" .
- buildah push "$CI_REGISTRY_IMAGE:latest"
- buildah logout "$CI_REGISTRY"

There are several important elements of this file to note.

  • We need to include at least the openshift tag, as previously mentioned, for our jobs to be picked up by the GitLab Runner Operator
  • We are using the official stable Buildah image hosted in Quay.io as our build image.
  • We set the storage driver to vfs due to issues with overlay-on-overlay filesystems. Using vfs is the simplest solution for now.
  • We change $HOME to /tmp to be sure we are able to write, since most container filesystems in OpenShift will be read-only.

The last section, script, is a list of the commands our build job will run. Here we utilize GitLab CI's predefined variables to sign into the GitLab container registry, build and tag our image, and finally push the image to the registry before logging out.

2. Writing the Containerfile for our custom Silverblue image

After adding the gitlab-ci.yml to our repository, we also need to add the Containerfile that we want to build. For our custom Fedora Silverblue image, I relied on the great work being done in the Universal Blue community. They have been working on various versions of Silverblue for different usecases and are an excellent resource if you or your team are interested in creating customized, immutable base images for Fedora Silverblue systems.

I thought it would be helpful to create a base image that includes the most recent releases of all the OpenShift and Operator tooling I use on a daily basis. Since we will be setting this to build daily, not only will my base image be updated with the most recent Fedora packages, but I will also never fall behind on the latest versions of these OpenShift and Operator tools that normally would require manual updates.


FROM quay.io/fedora-ostree-desktops/silverblue:${FEDORA_MAJOR_VERSION}
# Starting with Fedora 39, the new official location for these images is quay.io/fedora/fedora-silverblue
# See https://pagure.io/releng/issue/11047 for more information

# Install Openshift tools -- oc, opm, kubectl, operator-sdk, odo, helm, crc from official OpenShift sources
RUN curl -SL https://mirror.openshift.com/pub/openshift-v4/x86_64/clients/ocp/latest/opm-linux.tar.gz | tar xvzf - -C /usr/bin
RUN curl -SL https://mirror.openshift.com/pub/openshift-v4/x86_64/clients/operator-sdk/latest/operator-sdk-linux-x86_64.tar.gz | tar xvzf - --strip-components 2 -C /usr/bin
RUN curl -SL https://mirror.openshift.com/pub/openshift-v4/clients/oc/latest/linux/oc.tar.gz | tar xvzf - -C /usr/bin
RUN curl -SL https://mirror.openshift.com/pub/openshift-v4/x86_64/clients/helm/latest/helm-linux-amd64 -o /usr/bin/helm && chmod +x /usr/bin/helm
RUN curl -SL https://mirror.openshift.com/pub/openshift-v4/x86_64/clients/odo/latest/odo-linux-amd64 -o /usr/bin/odo && chmod +x /usr/bin/odo
RUN curl -SL https://mirror.openshift.com/pub/openshift-v4/x86_64/clients/crc/latest/crc-linux-amd64.tar.xz | tar xfJ - --strip-components 1 -C /usr/bin

# Install awscli
RUN curl -SL https://awscli.amazonaws.com/awscli-exe-linux-x86_64.zip -o awscliv2.zip && unzip awscliv2.zip && ./aws/install --bin-dir /usr/bin --install-dir /usr/bin

# Install overrides and additions, remove lingering files
RUN rpm-ostree install podman-docker
RUN rm -rf aws && \
rm -f awscliv2.zip && \
rm -f /usr/bin/README.md && \
rm -f /usr/bin/LICENSE

A short breakdown of what's happening in this Containerfile:

  • To start, we specify the version of Fedora we want to build, in this case the current stable version 38
  • Next, we specify the base image to use for our build, which is silverblue:38 after our FEDORA_MAJOR_VERSION substitution (please see the comments in the Containerfile on the location of these images)
  • In the largest section we run several curl commands to download all the OpenShift programs I want to install, making sure to put their binaries into the /usr/bin directory
  • We also install awscli which involves unpacking the .zip file and running the installation script
  • Lastly, we use rpm-ostree to install podman-docker from the Fedora package repositories (this essentially aliases any docker commands to podman for those of us used to running docker), and then delete some lingering files from the awscli extraction

As I mentioned before, for more Silverblue customization inspiration, please check out the community at Universal Blue. I relied heavily on their work in learning this workflow and they're already working on many new exciting applications of the bootable OCI capability in Silverblue.

3. Using and monitoring the pipeline jobs

We should add this Containerfile, or whatever Containerfile or Dockerfile you would rather build, to the root of our project repository since our gitlab-ci.yml specifies that buildah use the current working directory as the Containerfile argument. Depending on how you have commited all of the changes in this repository, you might already have had notifications about failed pipeline jobs, or if you're commiting all of this at once, you will see the first attempt at running the build job start now. You can watch the logs for your build by navigating to the CI/CD heading on your GitLab.com project page and then clicking either Pipelines or Jobs and clicking through until you see the log output for our job named buildah-build.

If we set everything up properly, you should see logs describing each step of the gitlab-ci.yml and Containerfile we wrote, concluding with "Job succeeded" when finished. If our job succeeds, then we should also be able to see our finished container in our project registry. On the left-hand navigation bar click Packages and registries and then Container Registry. You should see a single image named after your project with a single tag "latest." This image will be located at registry.gitlab.com/{YOUR_USERNAME}/{YOUR_REPOSITORY_NAME}.

The job as we wrote it will run with every commit to the main branch, but you can customize this behavior in the gitlab-ci.yml file. If we want to schedule regular builds, we can do so on our repository page in the CI/CD settings under the Schedule section. Click New schedule to configure the timing and frequency of your pipeline. You can learn more about GitLab.com pipeline scheduling here. For a custom Silverblue image you will probably want to build at least daily to match the build cadence of the official images.

Using our Custom Images

To actually use this image as a bootable base for Silverblue, you first need to install Fedora Silverblue from the official images if you don't have an existing installation. After your installation is finished and you've logged in, we can rebase our installation onto our custom image.

Please keep in mind that booting from OCI images is still an experimental feature, so use your own best judgement and discretion if you're using this on personal or production machines. Silverblue is built to be resilient to breakage, though, so if your custom image doesn't work as expected you should be able to rollback to the original base image. To be sure we don't remove that original base, we can run sudo ostree admin pin 0 to pin the current image. This makes sure the reference is not lost on subsequent updates, as Silverblue normally only keeps the current and previous image references. To actually rebase to our custom image, we run:

rpm-ostree rebase ostree-unverified-registry:registry.gitlab.com/{YOUR_USERNAME}/{YOUR_REPOSITORY_NAME}:latest

and then reboot.

After rebooting, we can verify we are running our custom image by looking at the output of rpm-ostree status. Your current deployment, identified by the circle/pip on the left-hand side, should show the ostree-unverified-registry URI of our custom image. You can also try running any of the OpenShift tools we added in a terminal, like oc, operator-sdk, or helm.

You should also see our pinned deployment with the old base reference in the output of rpm-ostree status. If you wish to rollback, just run rpm-ostree rollback and reboot. For more on Fedora Silverblue administration, please see the documentation


Assuming everything went without a hitch, we now have a self-hosted CI/CD pipeline running on our own OpenShift cluster that regularly creates new custom Silverblue images. Our runners should require no manual intervention unless we wish to reconfigure build job tags or create more runners to handle more concurrent jobs. Builds will start at our scheduled intervals and when we commit new code to the main branch, and if we are running our custom image on a Silverblue installation we simply need to run rpm-ostree update to pull in our daily updates.

This tutorial example is a simple illustration of the capabilities of the GitLab Runner Operator and the GitLab CI/CD system. Both are able to manage much more sophisticated CI/CD needs, and by running the Certified GitLab Runner Operator on OpenShift you're able to cut out much of the manual set-up and maintenance of the runners themselves, freeing up your time and effort for the actual contents and configuration of your builds.

I have created a reference repository with all the text files used in this tutorial here. Please also see a list of useful references below.

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