GitLab/Gitlab Runner

GitLab Runner is an application that works with GitLab CI/CD to run jobs in a pipeline. For more information see the official GitLab Runner documentation.

Current Gitlab Runner setup (T287504)

We're currently relying on WMCS VPSs for shared runner capacity. There is a project named gitlab-runners in which to provision new instances, and a profile to help provision Docker based runners on those instances. Note that a standalone puppetmaster in the same project stores the runner registration token under /etc/puppet/secret, and Puppet autosigning is turned off to protect the token value.

Setting up a new shared runner

To set up a new shared runner, following these steps.

1. Create a new WMCS VPS instance.
   1. Log in to [1] and navigate to the gitlab-runners project.
   2. Launch a new Debian buster instance, following the runner-{nnnn} naming convention.
   3. Add profile::gitlab::runner to the instance's Puppet Classes under the Puppet Configuration tab.
2. Wait until the new instance has fully provisioned and you can successfully ssh to the running instance using your authorized key. (This typically takes a few minutes.)
3. Do the little SSL dance that is required of instances that use a standalone puppetmaster.
   1. On the new runner (runner-{nnnn}.gitlab-runners.eqiad1.wikimedia.cloud).
      1. Run sudo rm -rf /var/lib/puppet/ssl to remove the existing SSL certs used by the default puppetmaster.
      2. Run sudo -i puppet agent --test --verbose to have the puppet client generate a new SSL cert.
   2. On gitlab-runners-puppetmaster-01.gitlab-runners.eqiad1.wikimedia.cloud sign the new instance's SSL cert.
      1. Run sudo -i puppet cert list and find the new instance in the list.
      2. Run sudo -i puppet cert sign runner-{nnnn}.gitlab-runners.eqiad1.wikimedia.cloud to sign the client cert.
4. Run sudo -i puppet agent --test --verbose on the runner to ensure it has fully provisioned the profile::gitlab::runner profile.
5. Verify that the runner has successfully registered with our GitLab instance by viewing the runner list.

Future Gitlab Runner setup (T286958)

This section contains the requirements and plan for a future Gitlab-Runner setup. The goal is to find a secure, scalable and easy to build and maintain setup for the GitLab Runner infrastructure. GitLab Runner support various environments, such as Kubernetes, Docker, OpenShift or just Linux VMs. Furthermore a wide range of compute platforms can be leveraged, such as WMCS, Ganeti, bare metal hosts or public clouds. So this section tries to compare the different options and collect advantages and disadvantages. Privacy considerations can be found in the next section.

GitLab Runner environments

GitLab Runner can be installed:

• in Linux (using official packages)
• in container
• in Kubernetes (as helm chart or agent)
• in OpenShift
• in various other environments

The follow table compares the most important GitLab Runner environments available (see Install GitLab Runner):

Environment	Advantages	Disadvantages	Additional considerations
Linux	Easy to setup low maintenance Similar to current solution	Low elasticity, difficult to scale
Container	Easy to setup low maintenance	difficult to scale auto scaling needsdocker-machine
Kubernetes	High elasticity/auto scaling	Additional Kubernetes needed (for security) Additional cluster needs maintenance More difficult to setup	Could be used to strengthen Kubernetes knowledge Auto scaling needs elastic compute plattform Maybe a general purpose non-production cluster can be build?
OpenShift		not in use in WMF

Compute Plattforms

The following table compares the four main computing options for the GitLab Runner setup: WMCS, Ganeti, Bare Metal or Public Cloud.

Plattform	Advantages	Disadvantages	Additional considerations
WMCS	High elasticity Semi-trusted environment (?) Kubernetes auto scaling can leverage OpenStack	Only in Eqiad	Elasticity is bound to appropriate quotas Kubernetes on OpenStack is new and different from existing Kubernetes solutions
Ganeti	Trusted environment	medium elasticity
Bare metal	Trusted environment Similar environment to existing Kubernetes setups	Low elasticity Machines have to be ordered and racked	Could old/decommissioned machines be used as runners?
Public Cloud (e.g. GCP)	High elasticity Low maintenance Easy Kubernetes setup (e.g. GKE)	untrusted environment (see privacy section) Dependency to cloud provider	Public discussion about public cloud is needed Evaluation of privacy considerations is needed (see below)

Elastic demand

Typically the demand of computing resources for building code and running test is not constant. The usage of CI peaks around African, European and US Timezones and workdays (see Grafana dashboard and dashboard). So the ideal solution would adapt to this usage and scale computing resources up and down. This would maximize the utilization of resources and cover usage peaks. However this elasticity comes with costs. In general a dynamic provisioning of Runners is more complex than a static. Furthermore WMF has additional requirements regarding privacy (see next chapter) and being independent from external parties.

So even if a elastic Runner setup would be the better technical solution we have to ask if we really need high elasticity.

Further reading:

https://docs.gitlab.com/runner/enterprise_guide/#autoscaling-configuration-one-or-more-runner-managers-multiple-workers

https://docs.gitlab.com/runner/executors/kubernetes.html

https://docs.gitlab.com/runner/configuration/autoscale.html

Privacy considerations

Privacy is one core principal of WMF. So if public clouds are used we have to make sure this usage aligns with our privacy policy and doesn't cause any security risks.

We have to think about what data is transmitted to public clouds during builds and tests. Do we include secrets, passwords or private user data when running a job? Do we consider this data leaked/compromised when transmitted to public cloud machines?

We also have to think about how to secure the artifacts and test results of jobs running in public clouds. How do we implement trust? How do we check if artifacts (images, compiled code) or test results weren't compromised?

Monitoring of performance and usage

Gitlab-Runner export Prometheus metrics. This metrics should give insights in performance and usage. See Monitoring Gitlab Runner documentation.

However the Gitlab Runner exporter does not support authorization or https. So depending on where the Runners are hosted, a https proxy with authorization is required.

Open Questions:

Open questions:

• Do we need high elasticity now/in the near future?
• Do we want to open a discussion about public cloud usage and privacy?
• Do we want to be depended on public cloud offerings?
• Do we have the resources to plan, implement and maintain a additional Kubernetes Cluster?
• Is a GitLab Runner Kubernetes cluster the best way to accumulate Kubernetes knowledge?