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How Kubernetes volume is used for PVC to Pod Template


Kubernetes Volumes and Designating a PVC

Why we need Volume in Kubernetes?

Persistent volume claim (PVC) can have many benefits. Here, I want to let you know that what a volume is. Also, we will explore why do we actually need a volume with the Postgres, specifically.

Kubernetes Volumes and Designating a PVC

Kubernetes Volumes Internals

In this section, we will explore the uses of volume to persist the data outside of a container. So that the data is persisted across restarts of a given container. Let’s look at the volumes in Kubernetes.

In Kubernetes, Volume is a referred to a specific type of object. A few of the common objects are Deployment, or a Java Software Development service. In Kubernetes, a configuration file can be written, which will create a volume. In Kubernetes, that object is something that allows a container to store some persistent data at the Pod level. In addition to the use of volumes, we also have access to two other types of data storage mechanisms that are “Persistent Volume” and “Persistent Volume claim”.

Note: Volume is very different than a persistent volume and persistent volume claim.

Limitations of Volumes in Kubernetes

But one problem here. The volume is tied to the pod. If the pod crashes, the volume is also damaged. Volume will only survive if the container restarts within the pod. So, now you got to know that in the world of Kubernetes, a volume is not really appropriate for storing data for a database. It definitely can work in the sense that the container can restart but we are still kind of vulnerable to anything goes wrong at the pod level itself.

Volume vs Persistent Volume(PV)

Persistent Volume claim and persistent volume are also objects. They are present in Kubernetes. Here is the image to depict the differences between PVC and PV.

Kubernetes Volumes and Designating a PVC

Persistent Volume(PV) vs Persistent Volume Claim(PVC)

Summary PVC: PVC is basically an advertisement of options. Any of those options can be asked inside of the Pod configuration. Kubernetes will explore the existing stores of PV to provide the volume created beforehand. Or, it may consider creating one dynamically on the fly.

PVC Demo

Persistent Volume Claim Configuration File Overview:

PVC config file will advertise the possible storage options which can be attached to a Pod configuration. A YAML file will be created, which is named as “database-persistent-volume-claim-yaml” file.

database-persistent-volume-claim-yaml file:

Kubernetes Volumes and Designating a PVC


“kubectl describe storageclass”

So, when you execute the above command it gives the below output:

Kubernetes Volumes and Designating a PVC

Designating a PVC in a Pod Template

Now, I am going to create our Postgres deployment file as below:


Kubernetes Volumes and Designating a PVC

Please look at the “template” section of the above fie. This template is used for every pod i.e. created by this deployment. As “replicas” value I have set to 1, so there will always be one pod at a time. Now I am going to update the template section and will inform this pod that when it is created, it needs to request some type of long-term storage this is nothing but a persistent volume that meets all the requirements that are advertised by PVC configured in our database-persistent-volume-claim.yaml file.

Now, inside the “spec” section of our postgres-deployment-yaml file, I am going to add a new key-value pair. In the persistentVolumeClaim section, I will provide the name of our PVC file. I will be adding “volumes” of name “postgres-storage”.

Now our updated postgres-deployment-yaml file will look like as below:

Updated “postgres-deployment-yaml” file with Volumes configured:

Kubernetes Volumes and Designating a PVC


Note: I have given example here very specific to “PostgreSQL” database.

Applying a PVC:

“kubectl delete pvc database-persistent-volume-claim”

“kubectl delete pv your Persistent Volume Name”

Summary: So, here if we write any data to Postgress db and then for some reason kill that pod then ideally it will not wipe out any other data that had been stored inside the database. So, you can test this yourself by saving any data to Postgres.


Here in this article, you learned the internals of Kubernetes persistent volume claim and persistent volume. Also, this blog explained to you about the need for volumes in Kubernetes and demo on how to create and designate the PVC configuration files in Pod template through an example of Postgres deployment.


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