Mastering Kubernetes One Task at a Time - Persistent Storage Volumes with 'hostPath'-Sharing Volumes among Multiple Containers

sharing-volumes-multi-containers.sh

#!/usr/bin/bash

# Purpose: Persistent Storage Volumes with 'hostPath'-Sharing Volumes among Multiple Containers
# Blog Ref: https://medium.com/the-aws-way/mastering-kubernetes-one-task-at-a-time-persistent-storage-volumes-with-hostpath-ad645714bcc7
# GitHub Ref: https://github.com/jdluther2020/jdluther-kubernetes-io-tasks/

# Author's NOTE
#  1. # are comment lines
#  2. Command output wherever helpful is shown inside {}
#  3. Everything is executed on a local dev environment (MacOS)

#
#  OBJECTIVE 3 -SHARING VOLUMES AMONG MULTIPLE CONTAINERS
# - Create a pod with two containers sharing the same volume, one for writing, one for reading
#

# Create the pod manifest with two containers, one writer and another reader
# (to avoid shell variable interpretation, copy the manifest straight instead of cat command)
cat <<EOF | shared-volume-pod.yaml
apiVersion: v1
kind: Pod
metadata:
  name: shared-volume-pod
spec:
  containers:
  - name: main-container
    image: busybox
    command: ['sh', '-c', 'while true; do echo "`date` : $CONTAINER_NAME : Test Message" >> /outdir/log.txt; sleep 5; done']
    env:
    - name: CONTAINER_NAME
      value: "main-container"
    volumeMounts:
    - name: vol-shared
      mountPath: /outdir
  - name: sidecar-container
    image: alpine
    command: ['sh', '-c', 'tail -f /indir/log.txt']
    volumeMounts:
    - name: vol-shared
      mountPath: /indir
  volumes:
  - name: vol-shared
    hostPath:
      path: /usr/share
EOF

# Create pod
kubectl apply -f shared-volume-pod.yaml

# Check pod created successfully and list the hosted node
kubectl get pod shared-volume-pod -o wide
{
NAME                READY   STATUS    RESTARTS   AGE   IP           NODE                               NOMINATED NODE   READINESS GATES
shared-volume-pod   2/2     Running   0          34s   10.244.1.4   basic-multi-node-cluster-worker2   <none>           <none>
}

# Check log to see sidecar container output
kubectl logs shared-volume-pod -c sidecar-container
{
Mon Apr 10 07:11:17 UTC 2023 : main-container : Test Message
...
Mon Apr 10 07:13:12 UTC 2023 : main-container : Test Message
}

# END OF DEMONSTRATION