This page shows how to configure a Pod to use a PersistentVolumeClaim for storage. Here is a summary of the process:
A cluster administrator creates a PersistentVolume that is backed by physical storage. The administrator does not associate the volume with any Pod.
A cluster user creates a PersistentVolumeClaim, which gets automatically bound to a suitable PersistentVolume.
The user creates a Pod that uses the PersistentVolumeClaim as storage.
You need to have a Kubernetes cluster that has only one Node, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a single-node cluster, you can create one by using Minikube.
Familiarize yourself with the material in Persistent Volumes.
Open a shell to the Node in your cluster. How you open a shell depends on how
you set up your cluster. For example, if you are using Minikube, you can open a
shell to your Node by entering
In your shell, create a
/mnt/data directory, create an
echo 'Hello from Kubernetes storage' > /mnt/data/index.html
In this exercise, you create a hostPath PersistentVolume. Kubernetes supports hostPath for development and testing on a single-node cluster. A hostPath PersistentVolume uses a file or directory on the Node to emulate network-attached storage.
In a production cluster, you would not use hostPath. Instead a cluster administrator would provision a network resource like a Google Compute Engine persistent disk, an NFS share, or an Amazon Elastic Block Store volume. Cluster administrators can also use StorageClasses to set up dynamic provisioning.
Here is the configuration file for the hostPath PersistentVolume:
The configuration file specifies that the volume is at
/mnt/data on the
cluster’s Node. The configuration also specifies a size of 10 gibibytes and
an access mode of
ReadWriteOnce, which means the volume can be mounted as
read-write by a single Node. It defines the StorageClass name
manual for the PersistentVolume, which will be used to bind
PersistentVolumeClaim requests to this PersistentVolume.
Create the PersistentVolume:
kubectl apply -f https://k8s.io/examples/pods/storage/pv-volume.yaml
View information about the PersistentVolume:
kubectl get pv task-pv-volume
The output shows that the PersistentVolume has a
means it has not yet been bound to a PersistentVolumeClaim.
NAME CAPACITY ACCESSMODES RECLAIMPOLICY STATUS CLAIM STORAGECLASS REASON AGE task-pv-volume 10Gi RWO Retain Available manual 4s
The next step is to create a PersistentVolumeClaim. Pods use PersistentVolumeClaims to request physical storage. In this exercise, you create a PersistentVolumeClaim that requests a volume of at least three gibibytes that can provide read-write access for at least one Node.
Here is the configuration file for the PersistentVolumeClaim:
Create the PersistentVolumeClaim:
kubectl apply -f https://k8s.io/examples/pods/storage/pv-claim.yaml
After you create the PersistentVolumeClaim, the Kubernetes control plane looks for a PersistentVolume that satisfies the claim’s requirements. If the control plane finds a suitable PersistentVolume with the same StorageClass, it binds the claim to the volume.
Look again at the PersistentVolume:
kubectl get pv task-pv-volume
Now the output shows a
NAME CAPACITY ACCESSMODES RECLAIMPOLICY STATUS CLAIM STORAGECLASS REASON AGE task-pv-volume 10Gi RWO Retain Bound default/task-pv-claim manual 2m
Look at the PersistentVolumeClaim:
kubectl get pvc task-pv-claim
The output shows that the PersistentVolumeClaim is bound to your PersistentVolume,
NAME STATUS VOLUME CAPACITY ACCESSMODES STORAGECLASS AGE task-pv-claim Bound task-pv-volume 10Gi RWO manual 30s
The next step is to create a Pod that uses your PersistentVolumeClaim as a volume.
Here is the configuration file for the Pod:
Notice that the Pod’s configuration file specifies a PersistentVolumeClaim, but it does not specify a PersistentVolume. From the Pod’s point of view, the claim is a volume.
Create the Pod:
kubectl apply -f https://k8s.io/examples/pods/storage/pv-pod.yaml
Verify that the Container in the Pod is running;
kubectl get pod task-pv-pod
Get a shell to the Container running in your Pod:
kubectl exec -it task-pv-pod -- /bin/bash
In your shell, verify that nginx is serving the
index.html file from the
root@task-pv-pod:/# apt-get update root@task-pv-pod:/# apt-get install curl root@task-pv-pod:/# curl localhost
The output shows the text that you wrote to the
index.html file on the
Hello from Kubernetes storage
Storage configured with a group ID (GID) allows writing only by Pods using the same GID. Mismatched or missing GIDs cause permission denied errors. To reduce the need for coordination with users, an administrator can annotate a PersistentVolume with a GID. Then the GID is automatically added to any Pod that uses the PersistentVolume.
pv.beta.kubernetes.io/gid annotation as follows:
kind: PersistentVolume apiVersion: v1 metadata: name: pv1 annotations: pv.beta.kubernetes.io/gid: "1234"
When a Pod consumes a PersistentVolume that has a GID annotation, the annotated GID is applied to all Containers in the Pod in the same way that GIDs specified in the Pod’s security context are. Every GID, whether it originates from a PersistentVolume annotation or the Pod’s specification, is applied to the first process run in each Container.
Note: When a Pod consumes a PersistentVolume, the GIDs associated with the PersistentVolume are not present on the Pod resource itself.
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