What is the purpose of a PodDisruptionBudget (PDB) in Kubernetes?

A PodDisruptionBudget limits how many pods of a deployment can be unavailable simultaneously during voluntary disruptions like node drains, cluster upgrades, or scaling down.

apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
  name: api-pdb
spec:
  minAvailable: 2
  selector:
    matchLabels:
      app: api

Without a PDB, a cluster upgrade could drain multiple nodes simultaneously and take down your entire service. With minAvailable: 2, Kubernetes ensures at least 2 pods are always running.