What is a pod disruption budget?

Pod Disruption Budget (PDB) is a mechanism in Kubernetes that ensures a minimum number of application replicas are available during voluntary disruptions (such as node updates) or controlled shutdowns.

A PDB specifies either a minimum number or percentage of available pods (minAvailable), or a maximum number or percentage of unavailable pods (maxUnavailable). The Kubernetes API respects this budget and prevents operations that would violate the set limit. Such operations include:

• Deleting pods by controllers (Deployment, StatefulSet, etc.) during scale-down.
• Manually deleting pods with the kubectl drain command for node maintenance.

It only protects against voluntary disruptions, not forced ones (like node failures).

Example of a PDB for Deployment my-app:

apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
  name: my-app-pdb
spec:
  minAvailable: 80%  # At least 80% of pods must remain available
  selector:
    matchLabels:
      app: my-app  # Selects pods with label app: my-app

In this example, Kubernetes will not allow voluntary disruptions to reduce the number of available pods with the label app: my-app below 80% of their total.