Improve documentation of unsupported helm functions

[rowi1de]

Summary

The Helm section doesn’t clearly list all unsupported functions that would require native helm support https://argo-cd.readthedocs.io/en/stable/user-guide/helm/#random-data

Motivation

#7759 (reply in thread)

Currently it requires debugging to find out which part of a helm chart might not work in ArgoCD.

Proposal

The helm section of ArgoCD should list all helm functions like lookup or random data generation etc. that won’t work as expected.
In addition it could be considered to have a section with charts that have known issues and how the workaround look like.
If the list is in a parseable format, it could even be used to build a UI feature on top #14944

[crenshaw-dev]

There are several things in the FAQ page that could probably be duplicated/linked/moved to the Helm page.

[acelinkio]

I think it would be useful to have a specific page documenting any unsupported resources. Adding a brief description, symptoms, workarounds, comments (suggestions/references/wont fix/feature in progress/etc). Example:

Helm Hook Support

• Description: Helm releases offer simple orchestration using hooks. These hooks are not built into the core Kubernetes api. ArgoCD does offer some compatibility, but unable to differentiate between an install or upgrade. Read more: https://argo-cd.readthedocs.io/en/stable/user-guide/helm/#helm-hooks
• Symptoms: When installing an ArgoCD application leveraging a helm chart pre-upgrade job, the job could be missing required resources to run and hang.
• Workarounds:
  • Depends on what actions the hook is performing. One option is to equivalent command helm template | kubectl apply -f to avoid hooks.
• Comments:
  • Helm hooks should be avoided when possible. Any complex logic is best moved into an operator or controller.
  • No plans to reach parity support + link to architectural decision record
  • Add ability to ArgoCD Application to ignore specific annotations (not sure if there is a feature request)
  • Create GitHub action that other projects can use for validation (not sure if there is a feature request)
  • Links to relevant issues:
    • [IMPROVEMENT] Remove or Change Helm pre-upgrade hook to support ArgoCD longhorn/longhorn#6415

Not sure if this is the most desired format for FAQ, but would help tracking. There are a lot of philosophy missing in the docs. Akuity's white paper reminded me of this https://akuity.io/blog/argo-cd-flux-comparison/