Mastering Kubernetes One Task at a Time - Ephemeral Storage Volumes with 'emptyDir'-Memory or RAM-backed emptyDir volume

emptydir-memory.sh

#!/usr/bin/bash

# Purpose: Mastering Kubernetes One Task at a Time - Ephemeral Storage Volumes with 'emptyDir'-Memory or RAM-backed emptyDir volume
# Blog Ref: https://medium.com/the-aws-way/mastering-kubernetes-one-task-at-a-time-ephemeral-storage-volumes-with-emptydir-6cb08546b0ff
# 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 2 - MOUNT A TMPFS (RAM-BACKED FILESYSTEM) TO EMPTYDIR MEDIUM SPECIFICATION
# - Create a pod with an emptyDir volumes type using memory medium
# - Ref - https://kubernetes.io/docs/concepts/storage/volumes/#emptydir
# - Ref: SizeMemoryBackedVolumes feature gate - https://kubernetes.io/docs/reference/command-line-tools-reference/feature-gates/
#

cat <<EOF | tee emptydir-memory.yaml
apiVersion: v1
kind: Pod
metadata:
  name: emptydir-memory
spec:
  containers:
  - name: nginx-container
    image: nginx
    volumeMounts:
    - mountPath: /usr/share/nginx/html
      name: memory-volume
  - name: fedora-container
    image: fedora
    command: ['sh', '-c', 'while true; do echo "$HOSTNAME: `date` : Welcome to Nginx! Hosted on emptyDir Memory Volume!!" >> /html/index.html; sleep 10; done']
    volumeMounts:
    - name: memory-volume
      mountPath: /html
  volumes:
  - name: memory-volume
    emptyDir:
      medium: Memory
EOF

# Create pod
kubectl apply -f emptydir-memory.yaml
{
pod/emptydir-memory created
}

# Get pod status details and obtain POD_IP for next command
kubectl get -f emptydir-memory.yaml -o wide
{
NAME              READY   STATUS    RESTARTS   AGE   IP           NODE                              NOMINATED NODE   READINESS GATES
emptydir-memory   2/2     Running   0          16s   10.244.2.2   basic-multi-node-cluster-worker   <none>           <none>
}

# Access nginx web server via fedora container to make sure it's up and serving
kubectl exec emptydir-memory -c fedora-container -- curl -s 10.244.2.2
{
emptydir-memory: Fri Apr 14 01:37:17 UTC 2023 : Welcome to Nginx! Hosted on emptyDir Memory Volume!!
emptydir-memory: Fri Apr 14 01:37:27 UTC 2023 : Welcome to Nginx! Hosted on emptyDir Memory Volume!!
emptydir-memory: Fri Apr 14 01:37:37 UTC 2023 : Welcome to Nginx! Hosted on emptyDir Memory Volume!!
...
}

# Check the filesystem tmpfs mounted on /html.
# tmpfs memory backed volumes are sized to 50% of the memory on a Linux host unless sizeLimit specified.
# In the 'df' output, used and availale space should change as index.html grows every second.
kubectl exec emptydir-memory -c fedora-container -- df -H /html
{
Filesystem      Size  Used Avail Use% Mounted on
tmpfs           4.1G  4.1k  4.1G   1% /html
}

# Proceed to OBJECTIVE 3