CKAD field manual

Kubernetes PDB YAML example

A PDB limits voluntary eviction. Set minAvailable or maxUnavailable, and a selector on the Pod labels. drain respects it.

Two fighters stay inside a glowing ring while crew roll a third one off the pad. Two fighters stay inside a glowing ring while crew roll a third one off the pad.
Create 
kubectl create pdb web-pdb --selector=app=web --min-available=2
minAvailable 
apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
  name: web-pdb
spec:
  minAvailable: 2
  selector:
    matchLabels:
      app: web
  unhealthyPodEvictionPolicy: IfHealthyBudget
maxUnavailable 
apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
  name: web-pdb
spec:
  maxUnavailable: 1
  selector:
    matchLabels:
      app: web
Inspect 
kubectl get pdb
kubectl describe pdb web-pdb

Fields

minAvailable
Pods that must stay Ready. An integer, or a percent string such as "50%". A percent rounds up.
maxUnavailable
Pods that may be unavailable. It still fits when the replica count changes. A percent rounds up, so more Pods can be down than the percentage you wrote. This or minAvailable, not both. Every selected Pod must share one controller.
selector
Required. Match the Pod template labels. An empty selector matches every Pod in the namespace.
matchLabels
The Pod labels, not the Deployment metadata. A miss leaves ALLOWED DISRUPTIONS at 0.
unhealthyPodEvictionPolicy
IfHealthyBudget is the default. A Running Pod that is not Ready can leave only while currentHealthy is still at least desiredHealthy. AlwaysAllow evicts it even when the budget is already broken.
kubectl create pdb
Short name of poddisruptionbudget. --min-available or --max-unavailable, plus --selector. Add -n when the task names a namespace.
kubectl get
ALLOWED DISRUPTIONS is status.disruptionsAllowed. 0 means drain waits.
kubectl describe
Shows the selector, the budget, and currentHealthy against desiredHealthy.

Watch

  • Set minAvailable or maxUnavailable, never both. The API rejects the object. maxUnavailable still fits when the replica count changes, and only when every selected Pod belongs to the same controller. A bare Pod uses an integer minAvailable. minAvailable: 2 on a Deployment of 2 leaves disruptionsAllowed at 0.
  • selector must match the Pod template labels. An empty selector matches every Pod in the namespace. A selector that matches nothing reports ALLOWED DISRUPTIONS 0.
  • kubectl drain uses the Eviction API and waits while disruptionsAllowed is 0. kubectl delete pod does not check the PDB. A rolling update is not limited by it, and a node crash is not blocked by it. Raise replicas so one Pod can leave. Do not delete the PDB to finish the drain.
  • Healthy means Ready=True. IfHealthyBudget, the default, will not evict a Running Pod that is not Ready while the budget is already broken, so a CrashLoop can stall drain. AlwaysAllow evicts those Pods. Pending, Succeeded, and Failed Pods can always be evicted.

Official docs Specifying a Disruption Budget Disruptions

Practice these objects on a live cluster →