Build Gitaly Docker images in MRs

Context

The Terraform module we created to provision a development GKE cluster uses the GitLab Helm Chart to deploy the GitLa installation.

The chart defines the source repository where the Gitaly Docker image should be pulled from. The image is built as part of the CNG project via some sort of scheduled job. Images are only built when a new version of Gitaly is released via an Update Gitaly version MR in Rails (example).

For development purposes, it would be ideal if we can build ad-hoc Gitaly images against an MR branch (or any commit really) and test them in the GKE cluster.

Proposal

• Investigate a mechanism for building ad-hoc Gitaly images for use in GKE. Ideally the image should be built similarly to that of CNG to mimic a production deployment.
• Create a script, pipeline, triggered job, or something that automates the above. Ideally, a Gitaly developer that creates an MR should have the option of building a container image with a click of a button.
• Modify the Terraform module such that it's easy for developers to override the image repository.