emptyDir

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In Kubernetes, emptyDir is a type of ephemeral storage that provides a temporary directory shared between all containers in a Pod. This directory is created when the Pod is scheduled to a Node and is deleted when the Pod is removed. The emptyDir volume is often used for tasks that require temporary storage, such as caching intermediate files or sharing data between containers in the same Pod.

Key Aspects

Lifecycle: The emptyDirvolume is created as soon as the Pod is assigned to a Node and is destroyed when the Pod is deleted. If a container crashes and restarts within the same Pod, the data in the emptyDir persists across container restarts.
Storage Medium: By default, emptyDir uses the disk of the Node where the Pod is running. You can also specify that the emptyDirshould be memory-backed by setting the medium field to "Memory", which causes the data to be stored in RAM. This can provide faster access but at the cost of using up Node memory.
Usage Scenarios:
1. Scratch Space: Temporary files that do not need to persist beyond the Pod's lifetime.
2. Data Sharing: Sharing files between containers in the same Pod.
3. Caching: Storing intermediate data that can be safely discarded once the Pod is terminated.

Declaratively

Empty dir of single pod

ofl-empty-dir-volume-mount.yml
apiVersion: v1
kind: Pod
metadata:
    name: ofl-empty-dir-pod
spec:
    containers:
    - name: ofl-empty-dir-pod
      image: busybox
      command: ['sh', '-c', 'while true; do echo Success! >> /output/output.txt; sleep 10; done']
      volumeMounts:
      - name: output-vol
        mountPath: /output
    volumes:
    - name: output-vol
      hostPath:
        path: /var/datas

Run the following command to create ofl-empty-dir-pod
```
kubectl apply -f ofl-empty-dir-volume-mount.yml
```
- Inspect empty dir
  - Run the following command to list the pod
```
kubectl get pod 
```
  - Run the following command to describe the pod ofl-empty-dir-pod
```
kubectl describe pod ofl-empty-dir-pod
```
  - Run the following command to deep dig inside the pod analyses the volume behavior
```
kubectl exec -i -t ofl-empty-dir-pod -- /bin/sh
```

Empty dir multi container pod

ofl-empty-dir-shared-volume-multi-mount.yml
apiVersion: v1
kind: Pod
metadata:
  name: ofl-empty-dir-shared-volume
spec:
  containers:
  - name: myvolumes-container-1
    image: alpine
    command: ['sh', '-c', 'while true; do echo Success! >> output1.txt; sleep 3600; done']

    volumeMounts:
    - mountPath: /demo1
      name: demo-volume

  - name: myvolumes-container-2
    image: alpine
    command: ['sh', '-c', 'while true; do echo Success! >> output2.txt; sleep 3600; done']

    volumeMounts:
    - mountPath: /demo2
      name: demo-volume

  - name: myvolumes-container-3
    image: alpine 
    command: ['sh', '-c', 'while true; do echo Success! >> output3.txt; sleep 3600; done']

    volumeMounts:
    - mountPath: /demo3
      name: demo-volume

  volumes:
  - name: demo-volume
    emptyDir: {}

Run the following command to create ofl-empty-dir-shared-volume

kubectl apply -f ofl-empty-dir-shared-volume-multi-mount.yml

Inspect empty dir

Run the following command to list the pod

kubectl get pod

Run the following command to describe the pod ofl-empty-dir-pod

kubectl describe pod ofl-empty-dir-shared-volume

Run the following command to deep dig inside the pod analyses the volume behavior

kubectl exec -i -t ofl-empty-dir-shared-volume -c myvolumes-container-1 -- /bin/sh

kubectl exec -i -t ofl-empty-dir-shared-volume -c myvolumes-container-2 -- /bin/sh

kubectl exec -i -t ofl-empty-dir-shared-volume -c myvolumes-container-3 -- /bin/sh

Note: All containers in a Pod have read/write access to the same emptyDir - if they requested a mount point for it. Containers can access the emptyDir using the same or different mount points.

Clean up

Run the following command to clear all deployment in cluster
```
kubectl delete all --all
```