Merge pull request #6010 from jabellard/component-priority-class-name

Proposal: Add Support for Component Priority Class Configuration in Karmada Operator

docs/proposals/karmada-operator/component-priority-class-name/README.md

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+---
+title: Support Priority Class Configuration for Karmada Control Plane Components
+authors:
+- "@jabellard"
+reviewers:
+- "@RainbowMango"
+approvers:
+- "@RainbowMango"
+
+creation-date: 2025-01-01
+
+---
+
+# Support Priority Class Configuration for Karmada Control Plane Components
+
+## Summary
+
+This proposal aims to extend the Karmada operator by introducing support for configuring the priority class name for Karmada control plane components.
+By enabling users to configure a custom priority class name, this feature ensures critical components are scheduled with appropriate priority, enhancing overall system reliability and stability.
+
+## Motivation
+
+Currently, the priority class name for Karmada components is hardcoded to `system-node-critical` for some components, while others do not specify a priority class at all. This limitation can compromise 
+the reliability and stability of the system in environments where scheduling of critical components is essential.
+
+By allowing users to configure the priority class name, this feature ensures:
+
+- Greater control over scheduling of critical Karmada control plane components, enhancing system reliability and stability.
+- Alignment with organizational policies for resource prioritization and workload management.
+- Flexibility to adapt priority classes for specific operational environments and use cases.
+
+### Goals
+- Provide a mechanism for configuring the scheduling priority of all in-cluster Karmada control plane components.
+- Ensure the feature integrates seamlessly with existing deployments while maintaining backward compatibility.
+
+### Non-Goals
+
+- Address scheduling priorities for components outside the Karmada control plane.
+
+## Proposal
+
+Introduce a new optional `priorityClassName` field in the `CommonSettings` struct, which is used across all Karmada components.
+
+### API Changes
+
+```go
+// CommonSettings describes the common settings of all Karmada Components.
+type CommonSettings struct {
+	
+    // PriorityClassName specifies the priority class name for the component.
+    // If not specified, it defaults to "system-node-critical".
+    // +kubebuilder:default="system-node-critical"
+    // +optional
+    PriorityClassName string `json:"priorityClassName,omitempty"`
+    
+    // Other, existing fields omitted for brevity...
+}
+
+```
+### User Stories
+
+#### Story 1
+As an infrastructure engineer, I need to configure the priority class for Karmada control plane components to ensure critical components are reliably scheduled to ensure system stability and reliability.
+
+#### Story 2
+As an infrastructure engineer managing a multi-tenant cluster, I want the ability to override the default  priority class for Karmada control plane components with a custom priority class that aligns with my organization’s policies, ensuring reliable resource allocation and system stability across workloads.
+
+### Risks and Mitigations
+
+1. *Backward Compatibility*: Existing deployments might rely on the current hardcoded `system-node-critical` priority class for some components.
+
+    - *Mitigation*: The `priorityClassName` field defaults to `system-node-critical` when not explicitly specified, preserving the current behavior.
+
+## Design Details
+
+During the reconciliation process, the Karmada operator will:
+
+- Check if `priorityClassName` is specified in the component’s `CommonSettings`.
+- If specified:
+  - Apply the specified priority class to the component’s Pod spec.
+- If not specified:
+  - Default to `system-node-critical` to maintain backward compatibility.