website/v1.1/docs/user-guide/persistent-volumes/index.md

layout	title
docwithnav	How To Use Persistent Volumes

How To Use Persistent Volumes

The purpose of this guide is to help you become familiar with Kubernetes Persistent Volumes. By the end of the guide, we'll have nginx serving content from your persistent volume.

This guide assumes knowledge of Kubernetes fundamentals and that you have a cluster up and running.

See Persistent Storage design document for more information.

Provisioning

A Persistent Volume (PV) in Kubernetes represents a real piece of underlying storage capacity in the infrastructure. Cluster administrators must first create storage (create their Google Compute Engine (GCE) disks, export their NFS shares, etc.) in order for Kubernetes to mount it.

PVs are intended for "network volumes" like GCE Persistent Disks, NFS shares, and AWS ElasticBlockStore volumes. HostPath was included for ease of development and testing. You'll create a local HostPath for this example.

IMPORTANT! For HostPath to work, you will need to run a single node cluster. Kubernetes does not support local storage on the host at this time. There is no guarantee your pod ends up on the correct node where the HostPath resides.

{% highlight console %} {% raw %}

This will be nginx's webroot

$ mkdir /tmp/data01 $ echo 'I love Kubernetes storage!' > /tmp/data01/index.html {% endraw %} {% endhighlight %}

PVs are created by posting them to the API server.

{% highlight console %} {% raw %} $ kubectl create -f docs/user-guide/persistent-volumes/volumes/local-01.yaml NAME LABELS CAPACITY ACCESSMODES STATUS CLAIM REASON pv0001 type=local 10737418240 RWO Available {% endraw %} {% endhighlight %}

Requesting storage

Users of Kubernetes request persistent storage for their pods. They don't know how the underlying cluster is provisioned. They just know they can rely on their claim to storage and can manage its lifecycle independently from the many pods that may use it.

Claims must be created in the same namespace as the pods that use them.

{% highlight console %} {% raw %} $ kubectl create -f docs/user-guide/persistent-volumes/claims/claim-01.yaml

$ kubectl get pvc NAME LABELS STATUS VOLUME myclaim-1 map[]

A background process will attempt to match this claim to a volume.

The eventual state of your claim will look something like this:

$ kubectl get pvc NAME LABELS STATUS VOLUME myclaim-1 map[] Bound pv0001

$ kubectl get pv NAME LABELS CAPACITY ACCESSMODES STATUS CLAIM REASON pv0001 type=local 10737418240 RWO Bound default/myclaim-1 {% endraw %} {% endhighlight %}

Using your claim as a volume

Claims are used as volumes in pods. Kubernetes uses the claim to look up its bound PV. The PV is then exposed to the pod.

{% highlight console %} {% raw %} $ kubectl create -f docs/user-guide/persistent-volumes/simpletest/pod.yaml

$ kubectl get pods NAME READY STATUS RESTARTS AGE mypod 1/1 Running 0 1h

$ kubectl create -f docs/user-guide/persistent-volumes/simpletest/service.json $ kubectl get services NAME CLUSTER_IP EXTERNAL_IP PORT(S) SELECTOR AGE frontendservice 10.0.0.241 3000/TCP name=frontendhttp 1d kubernetes 10.0.0.2 443/TCP 2d {% endraw %} {% endhighlight %}

Next steps

You should be able to query your service endpoint and see what content nginx is serving. A "forbidden" error might mean you need to disable SELinux (setenforce 0).

{% highlight console %} {% raw %} $ curl 10.0.0.241:3000 I love Kubernetes storage! {% endraw %} {% endhighlight %}

Hopefully this simple guide is enough to get you started with PersistentVolumes. If you have any questions, join the team on Slack and ask!

Enjoy!