Pregunta 13 - Múltiples Containers y Volumen Compartido

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.

---

Vamos a crear un yaml a partir de una plantilla y configurarlo. Es bueno estar familiarizado con emptydir y environments de nodos pods. Primero se crean los pods, después se levantan los containers. Algunas variables pueden ser referenciadas del propio container.

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                                                                      # cambiar
    resources: {}
    env:                                                                          # agregar
    - name: MY_NODE_NAME                                                          # agregar
      valueFrom:                                                                  # agregar
        fieldRef:                                                                 # agregar
          fieldPath: spec.nodeName                                                # agregar
    volumeMounts:                                                                 # agregar
    - name: vol                                                                   # agregar
      mountPath: /vol                                                             # agregar
  - image: busybox:1.31.1                                                         # agregar
    name: c2                                                                      # agregar
    command: ["sh", "-c", "while true; do date >> /vol/date.log; sleep 1; done"]  # agregar
    volumeMounts:                                                                 # agregar
    - name: vol                                                                   # agregar
      mountPath: /vol                                                             # agregar
  - image: busybox:1.31.1                                                         # agregar
    name: c3                                                                      # agregar
    command: ["sh", "-c", "tail -f /vol/date.log"]                                # agregar
    volumeMounts:                                                                 # agregar
    - name: vol                                                                   # agregar
      mountPath: /vol                                                             # agregar
  dnsPolicy: ClusterFirst
  restartPolicy: Always
  volumes:                                                                        # agregar
    - name: vol                                                                   # agregar
      emptyDir: {}                                                                # agregar

Vamos a aplicar

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

# Vamos a verificar dentro de los pods algunas cosas
# Si la variable de entorno está correcta en el container1
k exec multi-container-playground -c c1 -- env | grep MY_NODE_NAME
MY_NODE_NAME=cluster1-node2

# El container3 c3 está ejecutando el comando tail que envía a la salida en consola, vamos a verificar el log
k logs multi-container-playground -c c3