Kubernetes Volumes : EmptyDir

Introduction

Kubernetes volumes are a key feature of the Kubernetes container orchestration platform that enables containers to store and access data.

A volume in Kubernetes provides a way to persist data beyond the lifetime of a single container and enables data sharing and communication between containers within a pod.

Emptydir is a temporary volume that exists only during the lifetime of a pod.

It can be used to share the data between two multi-container pods.

Internal Workflow and EmptyDir Volume Example

In the above example, We create the multi-container pod in which one container will print the current date in a file and another container will use the file as a webpage.

1. Number of nodes

    arun@Aruns-MacBook-Air ~ % kubectl get nodes
    NAME       STATUS     ROLES           AGE   VERSION
    master     Ready      control-plane   58d   v1.26.3
    worker01   Ready      <none>          58d   v1.26.3
    worker02   Ready      <none>          58d   v1.26.3
   

2. Create MultiContainer Pod (Debian and Nginx).

    apiVersion: v1
    kind: Pod
    metadata:
      name: mc1
    spec:
      volumes:
      - name: html
        emptyDir: {}
      containers:
      - name: 1st
        image: nginx
        volumeMounts:
        - name: html
          mountPath: /usr/share/nginx/html
      - name: 2nd
        image: debian
        volumeMounts:
        - name: html
          mountPath: /html
        command: ["/bin/sh", "-c"]
        args:
          - while true; do
              date >> /html/index.html;
              sleep 1;
            done
   

    arun@Aruns-MacBook-Air kubernetes_volumes % ka empty_dir_example.yaml
    pod/mc1 created
    arun@Aruns-MacBook-Air kubernetes_volumes %
   

3. Kubernetes will create the Emptydir volume in the worker node based on the pod scheduled. Here, Pod scheduled in the worker01 node so we logged in using ssh and will verify the Emptydir.

   Let's identify the Pod ID to identify the empty dir.

    arun@Aruns-MacBook-Air ~ % kubectl get po mc1 -o yaml | grep uid
      uid: 903cc457-1f31-4020-bd22-331adf89eda7
    arun@Aruns-MacBook-Air ~ %
   

    root@worker01:~# cd /var/lib/kubelet/pods/903cc457-1f31-4020-bd22-331adf89eda7/volumes/kubernetes.io~empty-dir/
   
    root@worker01:/var/lib/kubelet/pods/903cc457-1f31-4020-bd22-331adf89eda7/volumes/kubernetes.io~empty-dir# ls -lrt
    total 4
    drwxrwxrwx 2 root root 4096 May 28 17:35 html
   

4. In nginx pod, We mounted the volume in the "mountPath: /usr/share/nginx/html". so we can exec and identify the index.html created.

    arun@Aruns-MacBook-Air ~ % kubectl exec -it mc1 -c 1st -- bash
    root@mc1:/# ls -lrt /usr/share/nginx/html
    total 24
    -rw-r--r-- 1 root root 18618 May 28 17:46 index.html
   

5. Once Pod, We deleted emptydir also will be removed in worker node.

    root@worker01:/var/lib/kubelet/pods/903cc457-1f31-4020-bd22-331adf89eda7/volumes#
   

   End. Thanks!

   Please post your valuable comments.