Change a PV's accessmode from ReadWriteOnce to ReadWriteMany or vice versa for a workload deployment

Products

• VMware Tanzu Kubernetes Grid Integrated Edition
• VMware Tanzu Kubernetes Grid Integrated (TKGi)
• VMware Tanzu Kubernetes Grid Integrated Edition (Core)
• VMware Tanzu Kubernetes Grid Integrated Edition 1.x
• VMware Tanzu Kubernetes Grid Integrated EditionStarter Pack (Core)

Issue/Introduction

The aim of this article is to change a PV's accessmode from either:

 - ReadWriteOnce to ReadWriteMany

   OR

 - ReadWriteOnce to ReadWriteMany

Environment

TKGi - 1.18.3

Cause

Application requirements change and you either require PV to be access by:

 - Single Pod or Node

 - Multiple Pods or Nodes

 - High Availability requirement

 - Data Consistency

 - Cost Management

Resolution

Note below:

PV - Persistent Volume
PVC - Persistent Volume Claim
RWO - ReadWriteOnce
RWX - ReadWriteMany

Steps:

1. Backup existing yaml resources ie PV, PVC, Deployment

   kubectl get pvc <your-pvc> -n <your-pvc-namespace> -o yaml > <your-pvc-backup>.yaml

2. Backup the existing PV you wish to change RWO to RWX for also (this could be done using Velero)
   
   
3. Change spec.persistentVolumeReclaimPolicy to Retain - if not set already.

   kubectl patch pv <your-pv> -n <your-pv-namespace> -p '{"spec":{"persistentVolumeReclaimPolicy":"Retain"}}'

4. Scale down deployment pods to zero for all pods that use the PV. In my test I had a single pod so deleted it.

   kubectl scale --replicas=0 -n <your-deployment-namespace> deployment <your-deployment-name>

5. As per step 1 backup the associating PVC yaml before deleting the PVC.
   
   
6. Delete the PVC to free up the PV ie status = Released.

   kubectl delete pvc <your-pvc> -n <your-pvc-namespace>

7. Free PV status to become Available

   kubectl patch pv <your-pv> -n <your-pv-namespace> -p '{"spec":{"claimRef":{"uid":""}}}'

8. Change the PV access mode to RWX

   kubectl patch pv <your-pv> -n <your-pv-namespace> -p '{"spec":{"accessModes":["ReadWriteMany"]}}'

9. Recreate the PVC with RWX
   
   To do this edit your PVC backup yaml's spec.accessModes from below:

   ...
   
   spec:
     accessModes:
       - ReadWriteOnce
   
   ...

   to below:

   ...
   
   spec:
     accessModes:
       - ReadWriteMany
   
   ...

   -- or vice versa depending on which you are changing from/to.
   
   
10. Scale up deployment pods to required number for all pods in the deployment to use the PV

    kubectl scale --replicas=1 -n <your-deployment-namespace> deployment <your-deployment-name>

    Now all your workloads should commence to using your PV in RWO/RWX access mode.

    All containers should then be checked to see if they were able to attach the PV(s) as required.

11. Restore the spec.persistentVolumeReclaimPolicy to original setting - which may originally have been Retain.

    kubectl patch pv <your-pv> -n <your-pv-namespace> -p '{"spec":{"persistentVolumeReclaimPolicy":"Delete"}}'