Configurable Deployment labels in Kubernetes integration

Problem to solve

Setting-up Kubernetes integration with existing cluster results in ugly/complex environment names, because GitLab requires an app label. While this label is generally present, it is often not suitable for an environment name.

Further details

Example use case: we are deploying with Helm and the app labels are quite long as they include release name, stage and chart name. I would rather use a different label, such as gitlab-filter.

Proposal

• While keeping the app label as default selector, allow configuring custom Deployment filters (and also Pod filters, unless they are simplified as suggested in #6389 (closed))
• Very generic filters could be implemented with the kubectl --selector syntax [1]
  • such a filter could default to CI_ENVIRONMENT_POD_FILTER=app=$CI_ENVIRONMENT_SLUG
  • more complex example: CI_ENVIRONMENT_POD_FILTER=gitlab-filter=$CI_ENVIRONMENT_SLUG,stage=beta

What does success look like, and how can we measure that?

GitLab integration no longer requires an app label, but can be configured with different pod filter.

Links / references

[1]

Selector (label query) to filter on, supports '=', '==', and '!='.(e.g. -l key1=value1,key2=value2)