feat: add PodDisruptionBudget to kgateway helm chart

[frauniki]

Description

• Add PodDisruptionBudget to kgateway helm chart
  • Improvements to the kgateway control plane Helm chart #12129

Change Type

/kind new_feature

Changelog

Add PodDisruptionBudget to kgateway helm chart

Additional Notes

[Copilot]

Pull Request Overview

This PR adds PodDisruptionBudget (PDB) support to the kgateway Helm chart to provide high availability guarantees during cluster maintenance operations.

• Add configurable PodDisruptionBudget resource with support for minAvailable, maxUnavailable, and unhealthyPodEvictionPolicy settings
• Update image pullPolicy default from empty string to "IfNotPresent" for consistency
• Include comprehensive JSON schema validation for PDB configuration

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
install/helm/kgateway/values.yaml	Add podDisruptionBudget configuration section and fix pullPolicy default
install/helm/kgateway/values.schema.json	Add complete JSON schema with PDB validation rules
install/helm/kgateway/templates/pdb.yaml	Create PDB template with conditional rendering

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[Copilot]

The condition checks if the podDisruptionBudget key exists, but it should check if it's non-empty. An empty object {} will evaluate to true, creating a PDB with no spec fields. Use {{- if and .Values.podDisruptionBudget (or .Values.podDisruptionBudget.minAvailable .Values.podDisruptionBudget.maxUnavailable) }} instead.

Suggested change

	{{- if .Values.podDisruptionBudget }}
	{{- if and .Values.podDisruptionBudget (or .Values.podDisruptionBudget.minAvailable .Values.podDisruptionBudget.maxUnavailable) }}

[frauniki]

No, that's incorrect.
In Helm's if expression, the empty object {} evaluates to false.

[frauniki]

Hmm, it seems there was a temporary issue with quay.io.

[timflannagan]

@frauniki Thanks for taking a stab at this. I talked with a couple of maintainers offline, and we determined that PDB support needs more thought, discussion, etc as it has implications on the overall 2.x HA story, which is still being ironed out and actively worked on.

At a minimum, we need a tracking issue for this and likely a design doc. Can you create an issue? No worries if not, I'll queue one up sometime this week.

[timflannagan]

Closing as a result of #12173 (comment). I'll create a tracker for the PDB work.