PetSet Instantiation and Scaling

6th chunk of `content/en/blog/_posts/2016-08-00-Stateful-Applications-Using-Kubernetes-Datera.md`

09bc70352cbe9dcbc2566d6e155898ffa41614d8ede86a320000000100000896

        - containerPort: 80

          name: web

        volumeMounts:

        - name: pv-claim

          mountPath: /data

  volumeClaimTemplates:

  - metadata:

      name: pv-claim

      annotations:

        [volume.alpha.kubernetes.io/storage-class:](http://volume.alpha.kubernetes.io/storage-class:) anything

    spec:

      accessModes: ["ReadWriteOnce"]

      resources:

        requests:

          storage: 100Gi
  ```



We have the following PersistentVolume Claims available:



 ```
[root@tlx241 /]# kubectl get pvc

NAME                     STATUS    VOLUME        CAPACITY   ACCESSMODES   AGE

pv-claim-test-petset-0   Bound     pv-datera-0   0                        41m

pv-claim-test-petset-1   Bound     pv-datera-1   0                        41m

pv-claim-test-petset-2   Bound     pv-datera-2   0                        5s

pv-claim-test-petset-3   Bound     pv-datera-3   0                        2s
  ```



When this PetSet is provisioned, two pods get instantiated:



 ```
[root@tlx241 /]# kubectl get pods

NAMESPACE     NAME                        READY     STATUS    RESTARTS   AGE

default       test-petset-0               1/1       Running   0          7s

default       test-petset-1               1/1       Running   0          3s
  ```



Here is how the PetSet test-petset instantiated earlier looks like:




 ```
[root@tlx241 /]# kubectl describe petset test-petset

Name: test-petset

Namespace: default

Image(s): [gcr.io/google\_containers/nginx-slim:0.8](http://gcr.io/google_containers/nginx-slim:0.8)

Selector: app=nginx

Labels: app=nginx

Replicas: 2 current / 2 desired

Annotations: \<none\>

CreationTimestamp: Sun, 14 Aug 2016 19:46:30 -0700

Pods Status: 2 Running / 0 Waiting / 0 Succeeded / 0 Failed

No volumes.

No events.
  ```



Once a PetSet is instantiated, such as test-petset below, upon increasing the number of replicas (i.e. the number of pods started with that PetSet), more pods get instantiated and more PersistentVolume Claims get bound to new pods:



 ```
[root@tlx241 /]# kubectl patch petset test-petset -p'{"spec":{"replicas":"3"}}'

"test-petset” patched


[root@tlx241 /]# kubectl describe petset test-petset

Title: PetSet Instantiation and Scaling

Summary

This section demonstrates the instantiation of a PetSet with two pods, as shown by the `kubectl get pods` command. It then describes the PetSet using `kubectl describe petset`, displaying its configuration details. Finally, it shows how to scale a PetSet by patching it to increase the number of replicas, leading to the creation of additional pods and binding of PersistentVolumeClaims to these new pods.