Effect of pod disruption budget on a single replica deployment

Question

We have a deployment with a single replica. I have also set a pod disruption budget with minimumAvailability = 1

apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
  name: app
spec:
  minAvailable: 1
  selector:
    matchLabels:
      app: app-selector

I have seen behaviour where clusterAutoscaler doesn't wait for the minimumAvailability to be healthy, and kills the pod.

My question is, does having a pod disruption budget works with replica number = 1 & minimum availability = 1?

Answer 1

Don't mix up PDB and maxUnavailable or MaxSurge : there are not the same..

• PDB prevents you from scaling down your app against volontary disruptions only, like cluster upgrades where you drain a node for exemple
• minAvailable define how many pods should remain up on rollout.
• maxSurge define how many pods should be added on rollout

Why do we need PodDisruptionBudget on AKS?

https://kubernetes.io/docs/tasks/run-application/configure-pdb/ https://kubernetes.io/docs/concepts/workloads/controllers/deployment/#rolling-update-deployment