Empty dir: Way to store non volatile store in K8s in zero touch approach

Introduction

Laymen explanation

Consider that you like to share some data to different container in same POD. For example, a container needs to watch performance parameter of another container, then another container can dump this data to this shared space. This document speaks about this.

Technical explanation

An emptyDir volume is first created when a Pod is assigned to a Node, and exists as long as that Pod is running on that node. As the name says, it is initially empty. Containers in the Pod can all read and write the same files in the emptyDir volume, though that volume can be mounted at the same or different paths in each Container. When a Pod is removed from a node for any reason, the data in the emptyDir is deleted forever.

Example POD yaml

apiVersion: v1

kind: Pod

metadata:

name: test-pd

spec:

containers:

- image: k8s.gcr.io/test-webserver

name: test-container

volumeMounts:

- mountPath: /cache

name: cache-volume

volumes:

- name: cache-volume

emptyDir: {}

In memory file sharing

By default, emptyDir volumes are stored on whatever medium is backing the node - that might be disk or SSD or network storage, depending on your environment. However, you can set the emptyDir.medium field to "Memory"to tell Kubernetes to mount a tmpfs (RAM-backed filesystem) for you instead. While tmpfs is very fast, be aware that unlike disks, tmpfs is cleared on node reboot and any files you write will count against your Container’s memory limit.

Reference

https://kubernetes.io/docs/concepts/storage/volumes/#emptydir