apiVersion: v1
kind: Pod
metadata:
  name: shared-storage-example
spec:
  volumes:
    - name: shared-data
      emptyDir: {}
  containers:
    - name: container-1
      image: nginx
      volumeMounts:
        - name: shared-data
          mountPath: /usr/share/nginx/html
    - name: container-2
      image: debian
      volumeMounts:
        - name: shared-data
          mountPath: /data
      command: ["/bin/sh"]
      args: ["-c", "echo Hello world > /data/index.html"]

This simple configuration doesn't work in Rancher 1. Started 1 deployment with this config 2. Increased the pods in the container to 3 3. The files created in

/data

are NOT shared between the 3 containers I do not want to use persistent volume claims because I don't need them to be persistent, I just need a folder to shared data ONLY between the pods in a deployment and for that data to be destroyed when the deployment is deleted

Nor is it supposed to. An emptyDir is shared between multiple containers in one pod, not between multiple pods in a deployment (which may be scheduled to different nodes).

Any idea how to share between pods in a deployment without Longhorn or NFS?

I mean there are other similar things, but you cannot share storage without.. shared.. storage A hostPath will work if you have exactly one node (or are ok with one set of data per node shared with pods on a given node, but separate from other nodes)