[root@master coredns]# k explain pv.spec
KIND:     PersistentVolume
VERSION:  v1
RESOURCE: spec <Object>
DESCRIPTION:
     Spec defines a specification of a persistent volume owned by the cluster.
     Provisioned by an administrator. More info:
     https://kubernetes.io/docs/concepts/storage/persistent-volumes#persistent-volumes
     PersistentVolumeSpec is the specification of a persistent volume.
FIELDS:
   accessModes  <[]string>
     AccessModes contains all ways the volume can be mounted. More info:
     https://kubernetes.io/docs/concepts/storage/persistent-volumes#access-modes
   awsElasticBlockStore <Object>
     AWSElasticBlockStore represents an AWS Disk resource that is attached to a
     kubelet's host machine and then exposed to the pod. More info:
     https://kubernetes.io/docs/concepts/storage/volumes#awselasticblockstore
   azureDisk  <Object>
     AzureDisk represents an Azure Data Disk mount on the host and bind mount to
     the pod.
   azureFile  <Object>
     AzureFile represents an Azure File Service mount on the host and bind mount
     to the pod.
   capacity <map[string]string>
     A description of the persistent volume's resources and capacity. More info:
     https://kubernetes.io/docs/concepts/storage/persistent-volumes#capacity
   cephfs <Object>
     CephFS represents a Ceph FS mount on the host that shares a pod's lifetime
   cinder <Object>
     Cinder represents a cinder volume attached and mounted on kubelets host
     machine. More info: https://examples.k8s.io/mysql-cinder-pd/README.md
   claimRef <Object>
     ClaimRef is part of a bi-directional binding between PersistentVolume and
     PersistentVolumeClaim. Expected to be non-nil when bound. claim.VolumeName
     is the authoritative bind between PV and PVC. More info:
     https://kubernetes.io/docs/concepts/storage/persistent-volumes#binding
   csi  <Object>
     CSI represents storage that is handled by an external CSI driver (Beta
     feature).
   fc <Object>
     FC represents a Fibre Channel resource that is attached to a kubelet's host
     machine and then exposed to the pod.
   flexVolume <Object>
     FlexVolume represents a generic volume resource that is
     provisioned/attached using an exec based plugin.
   flocker  <Object>
     Flocker represents a Flocker volume attached to a kubelet's host machine
     and exposed to the pod for its usage. This depends on the Flocker control
     service being running
   gcePersistentDisk  <Object>
     GCEPersistentDisk represents a GCE Disk resource that is attached to a
     kubelet's host machine and then exposed to the pod. Provisioned by an
     admin. More info:
     https://kubernetes.io/docs/concepts/storage/volumes#gcepersistentdisk
   glusterfs  <Object>
     Glusterfs represents a Glusterfs volume that is attached to a host and
     exposed to the pod. Provisioned by an admin. More info:
     https://examples.k8s.io/volumes/glusterfs/README.md
   hostPath <Object>
     HostPath represents a directory on the host. Provisioned by a developer or
     tester. This is useful for single-node development and testing only!
     On-host storage is not supported in any way and WILL NOT WORK in a
     multi-node cluster. More info:
     https://kubernetes.io/docs/concepts/storage/volumes#hostpath
   iscsi  <Object>
     ISCSI represents an ISCSI Disk resource that is attached to a kubelet's
     host machine and then exposed to the pod. Provisioned by an admin.
   local  <Object>
     Local represents directly-attached storage with node affinity
   mountOptions <[]string>
     A list of mount options, e.g. ["ro", "soft"]. Not validated - mount will
     simply fail if one is invalid. More info:
     https://kubernetes.io/docs/concepts/storage/persistent-volumes/#mount-options
   nfs  <Object>
     NFS represents an NFS mount on the host. Provisioned by an admin. More
     info: https://kubernetes.io/docs/concepts/storage/volumes#nfs
   nodeAffinity <Object>
     NodeAffinity defines constraints that limit what nodes this volume can be
     accessed from. This field influences the scheduling of pods that use this
     volume.
   persistentVolumeReclaimPolicy  <string>
     What happens to a persistent volume when released from its claim. Valid
     options are Retain (default for manually created PersistentVolumes), Delete
     (default for dynamically provisioned PersistentVolumes), and Recycle
     (deprecated). Recycle must be supported by the volume plugin underlying
     this PersistentVolume. More info:
     https://kubernetes.io/docs/concepts/storage/persistent-volumes#reclaiming
   photonPersistentDisk <Object>
     PhotonPersistentDisk represents a PhotonController persistent disk attached
     and mounted on kubelets host machine
   portworxVolume <Object>
     PortworxVolume represents a portworx volume attached and mounted on
     kubelets host machine
   quobyte  <Object>
     Quobyte represents a Quobyte mount on the host that shares a pod's lifetime
   rbd  <Object>
     RBD represents a Rados Block Device mount on the host that shares a pod's
     lifetime. More info: https://examples.k8s.io/volumes/rbd/README.md
   scaleIO  <Object>
     ScaleIO represents a ScaleIO persistent volume attached and mounted on
     Kubernetes nodes.
   storageClassName <string>
     Name of StorageClass to which this persistent volume belongs. Empty value
     means that this volume does not belong to any StorageClass.
   storageos  <Object>
     StorageOS represents a StorageOS volume that is attached to the kubelet's
     host machine and mounted into the pod More info:
     https://examples.k8s.io/volumes/storageos/README.md
   volumeMode <string>
     volumeMode defines if a volume is intended to be used with a formatted
     filesystem or to remain in raw block state. Value of Filesystem is implied
     when not included in spec.
   vsphereVolume  <Object>
     VsphereVolume represents a vSphere volume attached and mounted on kubelets
     host machine

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: nginx
  name: nginx
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  strategy: {}
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - image: nginx
        name: nginx
        resources: {}
        volumeMounts:
        - name: cache-volume
          mountPath: /cache
      volumes:
      - name: cache-volume
        emptyDir:
          medium:
          sizeLimit: 128Mi

[root@master ~]# k exec -it  nginx-f9df8c74f-gf9vz -- /bin/bash
root@nginx-f9df8c74f-gf9vz:/# cd cache/
root@nginx-f9df8c74f-gf9vz:/cache# echo "hello world " >test.fiel
root@nginx-f9df8c74f-gf9vz:/cache# 
exit

[root@slave1 ~]# find / -name test.fiel
/var/lib/kubelet/pods/db7976ed-4c86-4dae-ba2a-92d4dbc7b1e0/volumes/kubernetes.io~empty-dir/cache-volume/test.fiel
[root@slave1 ~]# cat /var/lib/kubelet/pods/db7976ed-4c86-4dae-ba2a-92d4dbc7b1e0/volumes/kubernetes.io~empty-dir/cache-volume/test.fiel
hello world 

[root@master ~]# k explain deploy.spec.template.spec.volumes.hostPath
KIND:     Deployment
VERSION:  apps/v1
RESOURCE: hostPath <Object>
DESCRIPTION:
     HostPath represents a pre-existing file or directory on the host machine
     that is directly exposed to the container. This is generally used for
     system agents or other privileged things that are allowed to see the host
     machine. Most containers will NOT need this. More info:
     https://kubernetes.io/docs/concepts/storage/volumes#hostpath
     Represents a host path mapped into a pod. Host path volumes do not support
     ownership management or SELinux relabeling.
FIELDS:
   path <string> -required-
     Path of the directory on the host. If the path is a symlink, it will follow
     the link to the real path. More info:
     https://kubernetes.io/docs/concepts/storage/volumes#hostpath
   type <string>
     Type for HostPath Volume Defaults to "" More info:
     https://kubernetes.io/docs/concepts/storage/volumes#hostpath