K
Q

Bind different Persistent Volume for each replica in a Kubernetes Deployment

1/1/2019

I am using a PVC with ReadWriteOnce access mode, which is used by a logstash Deployment which will run a stateful application and use this PVC.Each pod in the deployment will try to bind to the same persistent volume claim. In case of replicas > 1, it will fail (as it supports ReadWriteOnce, only the first one will be able to bind successfully). How do I specify that each pod is to be bound to a separate PV.

I don't want to define 3 separate yamls for each logstash replica / instance

apiVersion: apps/v1
kind: Deployment
metadata:
  name: logstash
spec:
  replicas: 3
  template:
    metadata:
      labels:
        app: logstash
    spec:
      containers:
        image: "logstash-image"
        imagePullPolicy: IfNotPresent
        name: logstash
        volumeMounts:
        - mountPath: /data
          name: logstash-data
      restartPolicy: Always
      volumes:
      - name: logstash-data
        persistentVolumeClaim:
          claimName: logstash-vol

Need a way to do volume mount of different PVs to different pod replicas.

-- Abhishek Jaisingh
kubernetes
persistent-volume-claims
persistent-volumes

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1 Answer

1/1/2019

With Deployments you cannot do this properly. You should use StatefulSet with PVC template to achieve your target. The part of your StatefulSet YAML code snippet could look like this:

...
volumeClaimTemplates:
- metadata:
    name: pv-data
  spec:
    accessModes: 
      - ReadWriteOnce
    resources:
      requests:
        storage: 5G

assuming you have 3 replicas, you will see the pods are created one by one sequentially, and the PVC is requested during the pod creation.

The PVC is named as volumeClaimTemplate name + pod-name + ordinal number and as result, you will have the list of newly created PVCs:

pv-data-<pod_name>-0
pv-data-<pod_name>-1
pv-data-<pod_name>-N

StatefulSet makes the names (not only names in fact) of your pods static and increments them depending on replica count, thats why every Pod will match its own PVC and PV respectively

Note: this is called dynamic provisioning. You should be familiar with configuring kubernetes control plane components (like controller-manager) to achieve this, because you will need configured persistent storage (one of them) providers and understand the retain policy of your data, but this is completely another question...

-- Konstantin Vustin
Source: StackOverflow