Kubernetes Deployment with StorageClass

Question

I have a StorageClass with provisioner: kubernetes.io/aws-ebs

And I have a deployment where I need to mount some volumes. So, I need to use this StorageClass

Here's my sc.yaml

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  annotations:
  name: gp2
parameters:
  fsType: ext4
  type: gp2
provisioner: kubernetes.io/aws-ebs
reclaimPolicy: Delete
volumeBindingMode: WaitForFirstConsumer

Here's my deployment.yaml

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: postgres
  namespace: var.namespace
spec:
  replicas: 1
  template:
    metadata:
      labels:
        app: postgres
    spec:
      containers:
        - name: postgres
          image: postgres:10.4
          imagePullPolicy: "IfNotPresent"
          ports:
            - containerPort: 5432
          envFrom:
            - configMapRef:
                name: postgres-config
          volumeMounts:
            - mountPath: /var/lib/postgresql/data
              name: postgredb
      # how can I specify my storage class here?
      volumes:
        - name: postgredb
          persistentVolumeClaim:
            claimName: postgres-pv-claim

I need to specify the storage class in my deployment. Can someone help me?

Answer 1

I need to specify the storage class in my deployment. Can someone help me?

Before we answer, first let's explain how StroageClass, PersistentVolume, Persistent Volume Claim.

Terminology

StroageClass

• We can look at StorageClass as a driver (Software).
• A driver which responsible for the "communication" with the storage hardware.
• Usually but not a must, the StorageClass is supplied by the Storage provider (hardware or virtual)

PersistentVolume

• A PersistentVolume (PV) is a piece of storage in the cluster that has been provisioned by an administrator or dynamically provisioned using Storage Classes.

PersistentVolumeClaim

• A PersistentVolumeClaim (PVC) is a request for storage by a user (Usually Pod)

---

General Diagram (describing K8 Storage objects)

TL;DR; Explanation

• You have physical storage (Disk, SSD, virtual, etc)
• Someone (usually the storage or the cloud provider) supplied you with the StorageClass object. By the way, you don't need to define/declare it most of the time and K8S will supply default storage for you (emptyDir).
• Then you define PersistentVolume (PV) which will "create" storage based upon the type (StorageClass) you require.
• Next step is to define PersistentVolumeClaim (PVC). The PVC is the allocation of the "physical" storage mounted from the (PV) which you defined in the previous step.
• The last step is to "assign" volume to your execution (Pod, Deployment, StatefulSet, etc) which is done using volumes.

** Notes

• As mentioned above most of the time you can simply use volumes without the need to define StorageClass or PV/PVC. Simply use a volume in the required Resources and K8S will take care of that for you.
• There are some exceptions (without getting into too many details here like StaefulSet). If no StorageClass is specified, then the default StorageClass will be used

---

Now let's answer your question

• You have defined a StorageClass

apiVersion: storage.k8s.io/v1
kind: StorageClass
...
provisioner: kubernetes.io/aws-ebs

• In your deployment, you specified volumes (identation left as as)

apiVersion: extensions/v1beta1
kind: Deployment
...
        
        # --> Here you define the actual mount path you need for your pods
        #     The name (PVC) is corresponding to the one you 
        #     defined below under volumes
        volumeMounts:
            - mountPath: /var/lib/postgresql/data
              name: postgredb
      # ->>>> how can I specify my storage class here?
      # You don't need to specify storage class, you need to define PVC,
      # This is the missing piece in your code.
      volumes:
        - name: postgredb
          persistentVolumeClaim:
            claimName: postgres-pv-claim

The missing piece ...

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: postgres-pv-claim ### <<< The name as mentioned above in your Deploymnet
  labels:
    app: postgres
spec:
  # The name of the storage class u defined earlier
  storageClassName: gp2

  # The access modes are:
  #   ReadWriteOnce - The volume can be mounted as read-write by a single node
  #   ReadWriteMany - The volume can be mounted as read-write by a many nodes
  #   ReadOnlyMany  - The volume can be mounted as read-only  by many nodes
  accessModes:
    - ReadWriteMany
  resources:
    requests:
      storage: 1Gi

---

Hope it helped you out.