Question 13 - Multi Containers and Pod Shared Volume

Question 13 | Multi Containers and Pod shared Volume

Use context: kubectl config use-context k8s-c1-H

Create a Pod named multi-container-playground in Namespace default with three containers, named c1, c2 and c3. There should be a volume attached to that Pod and mounted into every container, but the volume shouldn't be persisted or shared with other Pods.

Container c1 should be of image nginx:1.17.6-alpine and have the name of the node where its Pod is running available as environment variable MY_NODE_NAME.

Container c2 should be of image busybox:1.31.1 and write the output of the date command every second in the shared volume into file date.log. You can use while true; do date >> /your/vol/path/date.log; sleep 1; done for this.

Container c3 should be of image busybox:1.31.1 and constantly send the content of file date.log from the shared volume to stdout. You can use tail -f /your/vol/path/date.log for this.

Check the logs of container c3 to confirm correct setup.

---

Let's create a yaml from a template and configure it. It's good to be familiar with emptyDir and environment variables in pods. First pods are created then containers come up. Some variables can be referenced from the container itself.

k run multi-container-playground --image=nginx:1.17.6-alpine --dry-run=client -o yaml > opt/course/13/multi-container.yaml

vim opt/course/13/multi-container.yaml

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: multi-container-playground
  name: multi-container-playground
spec:
  containers:
  - image: nginx:1.17.6-alpine
    name: c1                                                                      # change
    resources: {}
    env:                                                                          # add
    - name: MY_NODE_NAME                                                          # add
      valueFrom:                                                                  # add
        fieldRef:                                                                 # add
          fieldPath: spec.nodeName                                                # add
    volumeMounts:                                                                 # add
    - name: vol                                                                   # add
      mountPath: /vol                                                             # add
  - image: busybox:1.31.1                                                         # add
    name: c2                                                                      # add
    command: ["sh", "-c", "while true; do date >> /vol/date.log; sleep 1; done"]  # add
    volumeMounts:                                                                 # add
    - name: vol                                                                   # add
      mountPath: /vol                                                             # add
  - image: busybox:1.31.1                                                         # add
    name: c3                                                                      # add
    command: ["sh", "-c", "tail -f /vol/date.log"]                                # add
    volumeMounts:                                                                 # add
    - name: vol                                                                   # add
      mountPath: /vol                                                             # add
  dnsPolicy: ClusterFirst
  restartPolicy: Always
  volumes:                                                                        # add
    - name: vol                                                                   # add
      emptyDir: {}                                                                # add

Let's apply

kubectl apply -f opt/course/13/multi-container.yaml
# checking
k get pod multi-container-playground
NAME                         READY   STATUS    RESTARTS   AGE
multi-container-playground   3/3     Running   0          95s

# Let's check some things inside the pods
# If the environment variable is correct in container1
k exec multi-container-playground -c c1 -- env | grep MY_NODE_NAME
MY_NODE_NAME=cluster1-node2

# Container c3 is running the tail command which outputs to console, let's check the log
k logs multi-container-playground -c c3