Kubernetes - Storage

Prerequisites

• Kubernetes
• kubectl

Assignment

• Create an ubuntu pod yaml with sleep infinity as a command:

kubectl run --image=ubuntu ubuntu -o yaml --dry-run=client --command sleep infinity | tee ubuntu_emptydir.yaml

• Update this specification so that it includes a volumeMount and an emptyDir volume:

cat <<EOF > ubuntu_emptydir.yaml
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: ubuntu
  name: ubuntu
spec:
  containers:
  - command:
    - sleep
    - infinity
    image: ubuntu
    name: ubuntu
    resources: {}
    volumeMounts:
    - mountPath: /cache
      name: cache-volume
  dnsPolicy: ClusterFirst
  restartPolicy: Always
  volumes:
  - name: cache-volume
    emptyDir: {
      medium: Memory,
    }
status: {}
EOF
```sh

```sh
kubectl apply -f ubuntu_emptydir.yaml

• Review the pods status and exce into it:

kubectl get pods -o wide

kubectl exec -it ubuntu -- bash

• Check the filesystem used by the cache directory - tmpfs:

cd cache; df -h .

• Check the performance of the memory based filesystem using dd:

dd if=/dev/zero of=output oflag=sync bs=1024k count=1000

exit

• When we get rid of this container it will also remove the emptyDir volume -

kubectl delete pod/ubuntu --now

Persistent Storage

• Review the storageclasses specification available in our cluster and claim policies:

kubectl get storageclass

kubectl explain storageclass | more

• Create a persistent volume using the k3s storageClass of local-path:

cat <<EOF > manual_pv.yaml
apiVersion: v1
kind: PersistentVolume
metadata:
  name: manual-pv001
spec:
  storageClassName: local-path
  capacity:
    storage: 10Gi
  accessModes:
    - ReadWriteOnce
  hostPath:
    path: "/var/lib/rancher/k3s/storage/manual-pv001"
    type: DirectoryOrCreate
EOF

kubectl apply -f manual_pv.yaml

• Check the available persistent volumes and note that the reclaim policy is set to Retain:

kubectl get pv

• Let’s now create a manual persistent volume claim against this persistent volume:

cat <<EOF > manual_pvc.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: manual-claim
spec:
  accessModes:
    - ReadWriteOnce
  volumeMode: Filesystem
  resources:
    requests:
      storage: 10Gi
  storageClassName: local-path
  volumeName: manual-pv001
EOF
```sh

```sh
kubectl apply -f manual_pvc.yaml

• Check the persistent volume claim:

kubectl get persistentvolumeclaim

kubectl get pvc

Dynamic PVC

• Create a dynamic version of our Persistent Volume Claim:

cat <<EOF > dynamic_pvc.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: dynamic-claim
spec:
  accessModes:
    - ReadWriteOnce
  volumeMode: Filesystem
  resources:
    requests:
      storage: 10Gi
  storageClassName: local-path
EOF

kubectl apply -f dynamic_pvc.yaml

• Check the status of the pvc:

kubectl get pvc

kubectl describe pvc/dynamic-claim

• Check the pv and to understand to check if a pv is available for the recently created pvc:

kubectl get pv

• Create a new pod:

kubectl run --image=ubuntu ubuntu -o yaml --dry-run=client --command sleep infinity | tee ubuntu_with_volumes.yaml

• Modify this to include volumeMounts and volumes for both our manual and dynamic pvc’s:

cat <<EOF > ubuntu_with_volumes.yaml
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: ubuntu
  name: ubuntu
spec:
  containers:
  - command:
    - sleep
    - infinity
    image: ubuntu
    name: ubuntu
    resources: {}
    volumeMounts:
    - mountPath: /manual
      name: manual-volume
    - mountPath: /dynamic
      name: dynamic-volume
  dnsPolicy: ClusterFirst
  restartPolicy: Always
  volumes:
    - name: manual-volume
      persistentVolumeClaim:
        claimName: manual-claim
    - name: dynamic-volume
      persistentVolumeClaim:
        claimName: dynamic-claim
status: {}
EOF

• As the k3s storageclass provisioner is very basic, we should use a nodeSelector to guide this pod to a specific node, check the labels for node/worker-1:

kubectl describe node/worker-1 | more

• And update the yaml to include a nodeSelector field:

cat <<EOF > ubuntu_with_volumes.yaml
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: ubuntu
  name: ubuntu
spec:
  nodeSelector:
    kubernetes.io/hostname: worker-1
  containers:
  - command:
    - sleep
    - infinity
    image: ubuntu
    name: ubuntu
    resources: {}
    volumeMounts:
    - mountPath: /manual
      name: manual-volume
    - mountPath: /dynamic
      name: dynamic-volume
  dnsPolicy: ClusterFirst
  restartPolicy: Always
  volumes:
    - name: manual-volume
      persistentVolumeClaim:
        claimName: manual-claim
    - name: dynamic-volume
      persistentVolumeClaim:
        claimName: dynamic-claim
status: {}
EOF

kubectl apply -f ubuntu_with_volumes.yaml

• Check that the pod is running:

kubectl get pod

• Check pv’s, A dynamic pv will have been created, notice the reclaim policies for both:

kubectl get pv

• Check pvc’s, they should now both be bound:

kubectl get pvc

• And let’s write data to our volumes, access the pod with an interactive shell:

kubectl exec -it ubuntu -- bash

• And if we check both of these, they are mounted volumes -

cd /manual; df -h .; cd /dynamic; df -h .

• Let’s write a text file to each of these and we’ll exit -

echo hello > /manual/test.txt; echo hello > /dynamic/test.txt; exit

• As these are persistent volumes, if we delete the pod and recreate it:

kubectl delete pod/ubuntu --now && kubectl apply -f ubuntu_with_volumes.yaml

• And again access this pod:

kubectl exec -it ubuntu -- bash

• We can see that our files will still exist as our volumes are persistent:

cat /manual/test.txt; cat /dynamic/test.txt

exit

• Before we go, let’s see what happens when we delete the pod and pvc’s:

kubectl delete pod/ubuntu pvc/dynamic-claim pvc/manual-claim --now

• If we check our pv’s, the manual one still exists as the Reclaim policy is set to Retain

kubectl get pv

• Finally we’ll clean this up and remove our files:

kubectl delete pv/manual-pv001 --now; rm -rf dynamic_pvc.yaml manual_pv* ubuntu_emptydir.yaml ubuntu_with_volumes.yaml