kubernetes pdb ALLOWED DISRUPTIONS is 0

Question

I am trying to deploy a PodDisruptionBudget for my deployment, but when I deploy this example

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

with this deployment

apiVersion: apps/v1
kind: Deployment
metadata:
  name: example-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      app: example-deployment-app
  template:
    metadata:
      labels:
        app: example-deployment-app
    spec:
        ...

I get the response

$ kubectl get pdb
NAME          MIN AVAILABLE   MAX UNAVAILABLE   ALLOWED DISRUPTIONS   AGE
example-pdb   1               N/A               0                     7s

What does it mean for "ALLOWED DISRUPTIONS" to be 0?

user_11560878 · Answer

As mentioned by Specifying a PodDisruptionBudget:

A PodDisruptionBudget has three fields:

A label selector .spec.selector to specify the set of pods to which it applies. This field is required.

.spec.minAvailable which is a description of the number of pods from that set that must still be available after the eviction, even in the absence of the evicted pod. minAvailable can be either an absolute number or a percentage.

.spec.maxUnavailable (available in Kubernetes 1.7 and higher) which is a description of the number of pods from that set that can be unavailable after the eviction. It can be either an absolute number or a percentage.

In your case the .spec.minAvailable is set to 1, so 1 Pod must always be available, even during a disruption.

Now looking at your Deployment's .spec.replicas is set to 1 which in combination of .spec.minAvailable: 1 means that there are no disruptions allowed for that config.

Take a look at the official example:

Use kubectl to check that your PDB is created.

Assuming you don't actually have pods matching app: zookeeper in your namespace, then you'll see something like this:
kubectl get poddisruptionbudgets
NAME     MIN AVAILABLE   MAX UNAVAILABLE   ALLOWED DISRUPTIONS   AGE
zk-pdb   2               N/A               0                     7s
If there are matching pods (say, 3), then you would see something like this:
kubectl get poddisruptionbudgets
NAME     MIN AVAILABLE   MAX UNAVAILABLE   ALLOWED DISRUPTIONS   AGE
zk-pdb   2               N/A               1                     7s
The non-zero value for ALLOWED DISRUPTIONS means that the disruption controller has seen the pods, counted the matching pods, and updated the status of the PDB.

You can get more information about the status of a PDB with this command:
kubectl get poddisruptionbudgets zk-pdb -o yaml

apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
  annotations:
…
  creationTimestamp: "2020-03-04T04:22:56Z"
  generation: 1
  name: zk-pdb
…
status:
  currentHealthy: 3
  desiredHealthy: 2
  disruptionsAllowed: 1
  expectedPods: 3
  observedGeneration: 1

You can see that if the .spec.minAvailable is set to 2 and there are 3 running Pods than the disruptionsAllowed is actually 1. You can check the same with your use case.

kubernetes pdb ALLOWED DISRUPTIONS is 0

1 Answers