13. Volumes

Volume types are described at https://kubernetes.io/docs/concepts/storage/volumes/

An ephemeral volume is linked to a pod and has the same lifespan as the pod, but is preserved across container restarts. One example of this is the empty volume type.
The hostPath volume type shares a directory between the host and the pod, similar to a bind mount in Docker.
A config map is a section of a YAML file that is mounted into the pod.

Note that many of the volume types listed in the link above are deprecated in favor of the Container Storage Interface (CSI).

13.1. HostPath Example

First, since Minikube is running in a Docker container, we need to mount our own filesystem into the Docker container:

$ minikube mount $HOME:/hosthome
📁  Mounting host path /home/yinchi into VM as /hosthome ...
    ▪ Mount type:   9p
    ▪ User ID:      docker
    ▪ Group ID:     docker
    ▪ Version:      9p2000.L
    ▪ Message Size: 262144
    ▪ Options:      map[]
    ▪ Bind Address: 192.168.49.1:36877
🚀  Userspace file server: ufs starting
✅  Successfully mounted /home/yinchi to /hosthome

📌  NOTE: This process must stay alive for the mount to be accessible ...

Next, we define the paths for mounting from Minikube into our deployment’s pod:

mydocs.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  creationTimestamp: null
  labels:
    app: mydocs
  name: mydocs
spec:
  replicas: 1
  selector:
    matchLabels:
      app: mydocs
  strategy: {}
  template:
    metadata:
      creationTimestamp: null
      labels:
        app: mydocs
    spec:
      volumes:
      - name: vol
        hostPath:
          path: /hosthome/k8s-docs/build/html
          type: Directory
      containers:
      - image: nginx
        name: nginx
        ports:
        - containerPort: 80
        volumeMounts:
        - mountPath: /usr/share/nginx/html
          name: vol

Finally, in a new terminal, apply the deployment, expose it as a service, and forward the appropiate port:

$ kubectl create -f mydocs.yaml
deployment.apps/mydocs created
$ kubectl expose deploy mydocs --type=NodePort
service/mydocs exposed
$ kubectl port-forward --address 0.0.0.0,:: svc/mydocs 8000:80
Forwarding from 0.0.0.0:8000 -> 80
Forwarding from [::]:8000 -> 80

To verify that changes in the host filesystem are reflected in the pod, we can delete our files:

(.venv)$ make clean
Removing everything under 'build'...

Reloading the site now should result in an error.