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f.storage.md

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Storage (7%)

Curriculum

  • Understand PersistentVolumeClaims for storage. en
  • Understand persistent volumes and know how to create them. en
  • Understand access modes for volumes. en
  • Understand persistent volume claims primitive. en
  • Understand Kubernetes storage objects. en
  • Know how to configure applications with persistent storage. en es

Exercise

  1. Create a configmap called config-volume from a literal value. Add the ConfigMap name under the volumes section of the Pod specification (/cm-vol).

    show 

    kubectl create cm cm-volume --from-literal=file=example-config-volumen

vim cm-pod.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: cm-volume-pod
spec:
  containers:
    - name: test-container
      image: k8s.gcr.io/busybox
      command: [ "/bin/sh", "-c", "ls /cm-vol ; cat /cm-vol/file" ]
      volumeMounts:
      - name: config-volume
        mountPath: /cm-vol
  volumes:
    - name: config-volume
      configMap:
        # Provide the name of the ConfigMap containing the file
        name: cm-volume
  restartPolicy: Never

kubectl create -f cm-pod.yaml 

kubectl logs cm-volume-pod

  2. Create a pod with a emptyDir volume in path /etc/empty using the nginx image.

    show 

    vim emptydir-pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: emptydir-pod
spec:
  containers:
  - image: nginx
    name: test-container
    volumeMounts:
    - mountPath: /etc/empty
      name: empty-volume
  volumes:
  - name: empty-volume
    emptyDir: {}

kubectl create -f emptydir-pod.yaml

kubectl exec emptydir-pod -- ls /etc | grep empty
kubectl exec emptydir-pod -- ls /etc/empty

  3. Mounts a directory (/tmp/host-test) from the host node’s filesystem into your Pod (/mnt/host-path). The host directory does not exist.

    show 

    vim host-pod.yaml
apiVersion: v1
kind: Pod
metadata:
  name: host-pod
spec:
  containers:
  - image: nginx
    name: test-container
    volumeMounts:
    - mountPath: /mnt/host-path
      name: host-volume
  volumes:
  - name: host-volume
    hostPath:
      # directory location on host
      path: /tmp/host-test
      type: DirectoryOrCreate  

kubectl create -f host-pod.yaml

# Check that the volume is empty
kubectl exec host-pod -- ls /mnt/host-path

  4. Check in which node the previous pod is running. Go to the node and create a file in the /tmp/host-test directory. Check the file in the pod.

    show 

    kubectl get pods -o wide
NAME            READY   STATUS      RESTARTS   AGE   IP          NODE     NOMINATED NODE   READINESS GATES
host-pod        1/1     Running     0          9s    10.40.0.2   node01   <none>           <none>

ssh node01 'echo "HELLO WORLD" > /tmp/host-test/hello-world'

kubectl exec host-pod -- ls /mnt/host-path
kubectl exec host-pod -- cat /mnt/host-path/hello-world

  5. Mounts a directory (/tmp/host-created) from the host node’s filesystem using type Directory into your Pod (/mnt/host-path-2).

    show 

    vim host-pod-2.yaml
apiVersion: v1
kind: Pod
metadata:
  name: host-pod-2
spec:
  containers:
  - image: nginx
    name: test-container
    volumeMounts:
    - mountPath: /mnt/host-path-2
      name: host-volume
  volumes:
  - name: host-volume
    hostPath:
      # directory location on host
      path: /tmp/host-created
      type: Directory  

kubectl create -f host-pod-2.yaml

kubectl describe pods host-pod-2
The pod status is ContainerCreating because the host-volume volume can not mount the /tmp/host-created host directory.

  6. Resolve the previous problem. Do not change the type.

    show 

    ssh nodeX
mkdir /tmp/host-created

  7. Create a secret called secret-vol from a literal value (user=john,password=pass123). Add the secret name under the volume section of the Pod specification (/tmp/passwords).

    show 

    kubectl create secret generic secret-vol --from-literal=user=john --from-literal=password=pass123

vim secret-pod.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: secret-volume-pod
spec:
  containers:
    - name: test-container
      image: nginx
      volumeMounts:
      - name: secret-volume
        mountPath: /tmp/passwords
  volumes:
    - name: secret-volume
      secret:
        # Provide the name of the secret containing the files
        secretName: secret-vol
  restartPolicy: Never

kubectl create -f secret-pod.yaml

kubectl exec secret-volume-pod -- sh -c 'ls /tmp/passwords ; cat /tmp/passwords/user'

  8. Change the user field of the previous secret and check that the new data has been transferred to the pod.

    New user: eve

    echo -n 'eve' | base64 
ZXZl
    show 

    kubectl edit secrets secret-vol
apiVersion: v1
data:
  password: cGFzczEyMw==
  user: ZXZl # change the user
kind: Secret
metadata:
  creationTimestamp: "2019-09-25T05:28:54Z"
  name: secret-vol
  namespace: default
  resourceVersion: "1105"
  selfLink: /api/v1/namespaces/default/secrets/secret-vol
  uid: 5d3c5256-df55-11e9-895a-0242ac11000d
type: Opaque

# wait for aprox. 1 min
kubectl exec secret-volume-pod -- sh -c 'cat /tmp/passwords/user'  
eve

  9. Use the secret created in the previous step and mount the user key in "/tmp/users" and the password key in "/tmp/passwords" as files.

    show 

    kubectl create secret generic secret-vol --from-literal=user=eve --from-literal=password=pass123 
vim secret-pod-2.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: secret-volume-pod-2
spec:
  containers:
    - name: test-container
      image: nginx
      volumeMounts:
      - name: secret-user-volume
        mountPath: /tmp/users
      - name: secret-pass-volume
        mountPath: /tmp/passwords          
  volumes:
    - name: secret-user-volume
      secret:
        # Provide the name of the secret containing the files
        secretName: secret-vol
        items:
        -  key: user 
           path: user-1
    - name: secret-pass-volume
      secret:
        # Provide the name of the secret containing the files
        secretName: secret-vol
        items:
        -  key: password
           path: pass-1
  restartPolicy: Never