Using emptyDir Volume to Share Data Between Containers¶

Let's see how we can use emptyDir volume to share data between containers.

Here is the Docker Image used in this tutorial: reyanshkharga/nginx

Step 1: Create a Deployment With emptyDir Volume¶

Let's create a deployment as follows:

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apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: writer
        image: reyanshkharga/nginx:v1
        command: ["/bin/sh"]
        args: ["-c", "while true; do echo $(date -u) >> /writer-data/my-data.txt; sleep 5; done"]
        volumeMounts:
        - name: my-volume
          mountPath: /writer-data
      - name: reader
        image: busybox
        command: ["/bin/sh"]
        args: ["-c", "while true; do tail -f /reader-data/my-data.txt; sleep 5; done"]
        volumeMounts:
        - name: my-volume
          mountPath: /reader-data
      volumes:
      - name: my-volume
        emptyDir: {}

Observe the following:

1. We have added an emptyDir volume in the pod template
2. The pod has two containers named writer and reader
3. The emptyDir volume is mounted on /writer-data directory of the writer container
4. The emptyDir volume is mounted on /reader-data directory of the reader container
5. The writer container writes some data in the my-data.txt file every 5 seconds
6. The reader container reads the same data from my-data.txt file every 5 seconds

You might wonder why the contents of the /writer-data/my-data.txt and /reader-data/my-data.txt files are the same.

The reason is that the my-data.txt file is stored in the shared my-volume volume, which is mounted to both containers on different directories. So any changes made to the file in one container are immediately visible in the other container, since they are both accessing the same file in the shared volume.

Apply the manifest to create the deployment:

kubectl apply -f my-deployment.yml

Step 2: Verify Deployment and Pods¶

Let's verify if the emptyDir volume was mounted in both the containers.

1. Start a shell session inside the writer container:

   kubectl exec -it <pod-name> -c writer -- bash
   

2. Verify if /writer-data directory is present in the writer container:

   ls /writer-data
   

3. View the content of /writer-data/my-data.txt file:

   tail -f /writer-data/my-data.txt
   

4. Exit out of the writer container:

   exit
   

5. Start a shell session inside the reader container:

   kubectl exec -it <pod-name> -c reader -- sh
   

6. Verify if /reader-data directory is present in the reader container:

   ls /reader-data
   

7. View the content of /reader-data/my-data.txt file:

   tail -f /reader-data/my-data.txt
   

8. Exit out of the reader container:

   exit
   

9. View reader container logs:

   kubectl logs -f <pod-name> -c reader
   

Observations:

1. The content of my-data.txt is shared between writer and reader containers.
2. Any changes made to the my-data.txt file in the writer container are immediately visible in the reader container.
3. The reader container is able to read the shared data. (Verified by checking reader container logs)

Clean Up¶

Assuming your folder structure looks like the one below:

|-- manifests
│   |-- my-deployment.yml

Let's delete all the resources we created:

kubectl delete -f manifests/