kubernetes pdb ALLOWED DISRUPTIONS is 0 - kubernetes

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?

Answer 1

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.