PDB

Introduction

When users deploy highly available jobs or applications on Volcano, they often need to limit the number of pod replicas that can be evicted or destroyed simultaneously to avoid downtime. This constraint is managed via Kubernetes PodDisruptionBudget (PDB) resources.

The PDB Plugin ensures that Volcano respects user-defined PDB constraints during the scheduling process, specifically during eviction actions like reclaim, preempt, and shuffle.

Prerequisites

• Your Kubernetes version must be 1.21 or later.
• You must have created valid PodDisruptionBudget resources for your workloads.

Mechanism

The PDB Plugin registers several functions (ReclaimableFn, PreemptableFn, and VictimTasksFn) under the reclaim, preempt, and shuffle actions. It maintains a cache of PDBs using v1.PodDisruptionBudgetLister.

During eviction scenarios, the plugin filters out tasks whose eviction would violate the configured PDB constraints. It calculates the DisruptedPods (pods whose eviction was processed but not yet observed by the PDB controller) and ensures the remaining available replicas satisfy the budget.

Configuration

To enable the PDB Plugin, update the volcano-scheduler-configmap to include the pdb plugin in your configuration tiers.

actions: "reclaim, preempt, shuffle"
tiers:
- plugins:
  - name: pdb    # Enable the PDB plugin
  - name: priority
  - name: gang
  - name: conformance
- plugins:
  - name: overcommit
  - name: drf
  - name: predicates
  - name: proportion
  - name: nodeorder
  - name: binpack

Note: The PDB plugin will be actively invoked when actions like reclaim, preempt, or shuffle are executed in the scheduler workflow.