k8s | BSWEN

How to solve ValidationError(Deployment.spec): unknown field volumeClaimTemplates error?

Dec 29, 2024

Problem

When we install application in kubernetes(k8s), sometimes, we get the following error:

root@launch-advisor:~# kubectl apply -f deployment-redis.yaml

error: error validating "deployment-redis.yaml": error validating data: ValidationError(Deployment.spec): unknown field "volumeClaimTemplates" in io.k8s.api.apps.v1.DeploymentSpec; if you choose to ignore these errors, turn validation off with --validate=false

The content of deployment-redis.yaml is:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: redis
  namespace: ns-bswen
  labels:
    app: redis
spec:
  selector:
    matchLabels:
      app: redis
  replicas: 1
  template:
    metadata:
      labels:
        app: redis
    spec:
      containers:
        - name: redis
          image: redis:6.0.9
          ports:
            - containerPort: 6379
          command: ["redis-server", "/etc/redis/redis.conf"]
          volumeMounts:
            - name: "redis-conf"
              mountPath: /etc/redis/redis.conf
              subPath: redis_conf
            - name: "redis-data"
              mountPath: "/var/lib/redis"
      volumes:
        - name: "redis-conf"
          configMap:
            name: "redis"
        - name: "redis-data"
          persistentVolumeClaim:
            claimName: redis-pvc
  volumeClaimTemplates:
    - metadata:
        name: redis-pvc
        annotations:
          volume.beta.kubernetes.io/storage-class: "my-nfs-storage"
      spec:
        accessModes: ["ReadWriteOnce"]
        resources:
          requests:
            storage: 100Mi

Notice that the above yaml is using the kubernetes resource type Deployment.

Environment

Docker: Server Version: 19.03.13

Kubectl version

Client Version: version.Info{Major:"1", Minor:"17", GitVersion:"v1.17.3", GitCommit:"06ad960bfd03b39c8310aaf92d1e7c12ce618213", GitTreeState:"clean", BuildDate:"2020-02-13T18:06:54Z", GoVersion:"go1.13.8", Compiler:"gc", Platform:"darwin/amd64"}

Server Version: version.Info{Major:"1", Minor:"18", GitVersion:"v1.18.6", GitCommit:"dff82dc0de47299ab66c83c626e08b245ab19037", GitTreeState:"clean", BuildDate:"2020-07-15T16:51:04Z", GoVersion:"go1.13.9", Compiler:"gc", Platform:"linux/amd64"}

Reason

In Kubernetes (K8s), volumeClaimTemplates is a resource template used within StatefulSets to dynamically create persistent storage volumes (Persistent Volumes, PVs). VolumeClaimTemplates allow each Pod within a StatefulSet to have its own independent persistent storage, and PVCs (Persistent Volume Claims) corresponding to them can be automatically created through the template.

The role of volumeClaimTemplates:

Automate PVC creation: VolumeClaimTemplates enable you to automatically create PVCs for each Pod in a StatefulSet without manually configuring a PVC for each Pod. This is particularly useful for applications that require each Pod to have its own independent storage.
Ensure persistent storage: StatefulSets are primarily used for stateful applications (such as databases, distributed systems, etc.), which require ensuring that storage is not lost in cases of Pod restarts, migrations, etc. With volumeClaimTemplates, each Pod has its own PVC and mounted PV, ensuring data persistence.
Automatic binding of Persistent Volume (PV): Kubernetes automatically creates PVCs based on volumeClaimTemplates, and these PVCs are automatically bound to a suitable PV. This means that users do not need to manually manage the relationship between PVCs and PVs; Kubernetes automatically selects the appropriate PV based on storage resources and configured StorageClass.
Templated storage configuration: When using volumeClaimTemplates, you can define a template for PVCs (such as storage size, storage class, etc.), and Kubernetes will create corresponding PVCs for each Pod. This ensures that all Pods use the same storage configuration without the need to define storage details for each Pod individually.

But,

StatefulSet is useful for running things in cluster e.g Hadoop cluster, MySQL cluster, where each node has its own storage.

Solution

You can switch from Deployment to StatefulSet as follows:

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: redis
  namespace: ns-bswen
  labels:
    app: redis
spec:
  serviceName: redis
  selector:
    matchLabels:
      app: redis
  replicas: 1
  template:
    metadata:
      labels:
        app: redis
    spec:
      containers:
        - name: redis
          image: redis:6.0.9
          ports:
            - containerPort: 6379
          command: ["redis-server", "/etc/redis/redis.conf"]
          volumeMounts:
            - name: "redis-conf"
              mountPath: /etc/redis/redis.conf
              subPath: redis_conf
            - name: "redis-data"
              mountPath: "/var/lib/redis"
      volumes:
        - name: "redis-conf"
          configMap:
            name: "redis"
        - name: "redis-data"
          persistentVolumeClaim:
            claimName: redis-pvc
  volumeClaimTemplates:
    - metadata:
        name: redis-pvc
        annotations:
          volume.beta.kubernetes.io/storage-class: "my-nfs-storage"
      spec:
        accessModes: ["ReadWriteOnce"]
        resources:
          requests:
            storage: 100Mi