Using out-of-tree volume plugins with FlexVolume

FlexVolume became generally available in Kubernetes 1.8. It allows you to consume out-of-tree storage through a uniform API. Storage providers write a driver that you install on all nodes. The FlexVolume plugin can dynamically discover existing drivers. Here is an example of using a FlexVolume to bind to an external NFS volume:

apiVersion: v1
kind: Pod
metadata:
  name: nginx-nfs
  namespace: default
spec:
  containers:
  - name: nginx-nfs
    image: nginx
    volumeMounts:
    - name: test
      mountPath: /data
    ports:
    - containerPort: 80
  volumes:
  - name: test
    flexVolume:
      driver: "k8s/nfs"
      fsType: "nfs"
      options:
        server: "172.16.0.25"
        share: "dws\_nas\_scratch"

However, at this point I highly recommend you avoid using the FlexVolume plugin and utilize CSI plugins instead.