Nginx index.html is override With Shared Volume

Question

I have a Pod with an emptyDir volume mounted in two containers:

• nginx at /usr/share/nginx/html/
• busybox at /var/html/

If i create a file with html extension inside busybox container at /var/html this file is copied to nginx container in /usr/share/nginx/html and i cant figure out why this happens.

The same behavior happens in this documentation example: https://kubernetes.io/docs/tasks/access-application-cluster/communicate-containers-same-pod-shared-volume/

Pod Manifest:

apiVersion: v1
kind: Pod
metadata:
  name: web-server
  labels:
    book: kubernetes-in-action
    section: 6-2-1-Using-an-emptyDir-volume
spec:
  containers:
    - image: nginx
      name: web-server
      volumeMounts:
        - name: html-vol
          mountPath: /usr/share/nginx/html
    - image: busybox
      name: content-agent
      command: ["/bin/sh", "-c"]
      args: ["\
              echo \"$(date) | creating html file at var/html\"; \
              echo \"<h1> $(date) </h1>\" > var/html/front.html; \
              sleep 15; \
              while true; do \
                echo \"$(date) | append to html file at var/html\"; \
                echo \"<h1> $(date) </h1>\" >> var/html/front.html; \
                sleep 15; \
              done; \
            "]
      volumeMounts:
        - name: html-vol
          mountPath: /var/html
  volumes:
    - name: html-vol
      emptyDir: {}
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