Add an option to skip CRD installation via Helm chart values

[vanchaxy]

What would you like to be added:
I'd like an option to skip CRD installation. This could be done either by providing a toggle in the values.yaml (e.g., crds.enabled, similar to cert-manager), or by extracting the CRDs into a separate Helm chart (like Prometheus does).

Why is this needed:
Currently, it's not possible to skip CRD installation for just one Helm chart dependency. Because of this, when installing a Helm chart with two external-dns dependencies (e.g., for split DNS), the CRD is included twice. This raises a warning in tools like Argo CD.

[ivankatliarchuk]

This is a helm constraint, not something that chart could handle helm/helm#10540

For context, there have been past attempts to add similar features: https://github.com/kubernetes-sigs/external-dns/pulls?q=is%3Apr+helm+disable+crd+is%3Aclosed+

Another option is to remove CRD from the chart.

[ivankatliarchuk]

As a rule of thumb, if this is a production environment, it’s better to maintain your own Helm chart registry. Open-source charts are generally designed for broader, generic use cases.

[ivankatliarchuk]

ArgoCD supports feature to skip CRDs as it looks argoproj/argo-cd#8012. Where or not it fits all the use-cases difficult to predict.

[vanchaxy]

Most charts use ".Values.crds.enabled" or ".Values.installCRDs" to overcome this limitation and install CRD conditionally. Is there anything that prevents it from adding to the external-dns chart? It's quite easy to add and maintain (single boolean in values and single "if" on the top level of the CRD file).

[ivankatliarchuk]

There is definitely some UX value here, but the chances of this being accepted are quite low. This really needs to be addressed by the Helm tool or community itself, rather than introducing workarounds in charts.

The warning message is expected behaviour and is documented here: if the CRD already exists, it will be skipped with a warning.

I would consider this a workaround rather than a proper solution, as it doesn’t follow the recommended Helm approach, and Helm creators do not suggest doing proposed solution:
https://helm.sh/docs/chart_best_practices/custom_resource_definitions/

In fact there is even

This is also the reason behind removing templating support from CRDs.

So the proposed apprach was considered harmful and deprecated by the Helm maintianers.