Pod Disruption Budget (PDB) Plugin

Introduction

When users apply jobs to volcano, they may limit the number of Pod copies that are destroyed at the same time. This restriction is often limited by the PDB resources created by the user. So PDB plugin is provided to meet the PBD constraints set by the user during the Volcano scheduling process.

Usage

1. Firstly, please ensure that your k8s version is at least 1.21 and that you have created the PDB resource.

2. Secondly, user can open PDB Plugin via volcano-scheduler-configmap in following format:

     actions: "reclaim, preempt, shuffle"
     tiers:
     - plugins:
       - name: pdb
   

PDB Plugin can be used in any one action of reclaim, preempt, shuffle

Solution

The plugin register , ReclaimableFn, PreemptableFn and VictimTasksFn in Reclaim, Preempt and Shuffle action to filter out tasks that violate the PDB constraint.

The execution flow chart of filter process of pdb plugin is shown as below:

DisruptedPods contains information about pods whose eviction was processed by the API server eviction subresource handler but has not yet been observed by the PodDisruptionBudget controller.

About the Cache

The PDB plugin first registers informerFactory.Policy().V1().PodDisruptionBudgets() in newSchedulerCache() function.

Then the plugin adds v1.PodDisruptionBudgetLister variable to type definition and inits it with informerFactory.Policy().V1().PodDisruptionBudgets().Lister() in New() function.

Finally the plugin uses this Lister to list the PDBs from the informer cache.

Feature Interaction

1. By now we only need 1 argument sla-waiting-time, so I add it into annotations for simplicity and invocation, but when sla plugin is extended with more arguments, a better way to invoke this plugin may be job plugin like svc and ssh.