--- title: "Kubernetes Persistent volume to store persistent data" description: "This post summarizes how to use the Kubernetes persistent volume in the deployment" canonical_url: "https://www.bigbinary.com/blog/using-kubernetes-persistent-volume-for-persistent-data-storage" markdown_url: "https://www.bigbinary.com/blog/using-kubernetes-persistent-volume-for-persistent-data-storage.md" --- # Kubernetes Persistent volume to store persistent data This post summarizes how to use the Kubernetes persistent volume in the deployment - Author: Rahul Mahale - Published: April 12, 2017 - Categories: Kubernetes In one of our projects we are running Rails application on [Kubernetes](http://kubernetes.io/) cluster. It is proven tool for managing and deploying docker containers in production. In kubernetes containers are managed using [deployments](http://kubernetes.io/docs/user-guide/deployments/) and they are termed as [pods](http://kubernetes.io/docs/user-guide/pods/). `deployment` holds the specification of pods. It is responsible to run the pod with specified resources. When `pod` is restarted or `deployment` is deleted then data is lost on pod. We need to retain data out of pods lifecycle when the `pod` or `deployment` is destroyed. We use docker-compose during development mode. In docker-compose linking between host directory and container directory works out of the box. We wanted similar mechanism with Kubernetes to link volumes. In kubernetes we have various types of [volumes](https://kubernetes.io/docs/user-guide/volumes/#types-of-volumes1) to use. We chose [persistent volume](http://kubernetes.io/docs/user-guide/persistent-volumes/) with [AWS EBS](https://aws.amazon.com/ebs/) storage. We used persistent volume claim as per the need of application. As per the [Persistent Volume's definition](http://kubernetes.io/docs/user-guide/persistent-volumes/) (PV) Cluster administrators must first create storage in order for Kubernetes to mount it. Our Kubernetes cluster is hosted on AWS. We created AWS EBS volumes which can be used to create persistent volume. Let's create a sample volume using aws cli and try to use it in the deployment. ```bash aws ec2 create-volume --availability-zone us-east-1a --size 20 --volume-type gp2 ``` This will create a volume in `us-east-1a` region. We need to note `VolumeId` once the volume is created. ```bash $ aws ec2 create-volume --availability-zone us-east-1a --size 20 --volume-type gp2 { "AvailabilityZone": "us-east-1a", "Encrypted": false, "VolumeType": "gp2", "VolumeId": "vol-123456we7890ilk12", "State": "creating", "Iops": 100, "SnapshotId": "", "CreateTime": "2017-01-04T03:53:00.298Z", "Size": 20 } ``` Now let's create a persistent volume template `test-pv` to create volume using this EBS storage. ```yaml kind: PersistentVolume apiVersion: v1 metadata: name: test-pv labels: type: amazonEBS spec: capacity: storage: 10Gi accessModes: - ReadWriteMany awsElasticBlockStore: volumeID: fsType: ext4 ``` Once we had template to create persistent volume, we used [kubectl](http://kubernetes.io/docs/user-guide/kubectl/) to launch it. Kubectl is command line tool to interact with Kubernetes cluster. ```bash $ kubectl create -f test-pv.yml persistentvolume "test-pv" created ``` Once persistent volume is created you can check using following command. ```bash $ kubectl get pv NAME CAPACITY ACCESSMODES RECLAIMPOLICY STATUS CLAIM REASON AGE test-pv 10Gi RWX Retain Available 7s ``` Now that our persistent volume is in available state, we can claim it by creating [persistent volume claim policy](http://kubernetes.io/docs/user-guide/persistent-volumes/#persistentvolumeclaims). We can define persistent volume claim using following template `test-pvc.yml`. ```yaml kind: PersistentVolumeClaim apiVersion: v1 metadata: name: test-pvc labels: type: amazonEBS spec: accessModes: - ReadWriteMany resources: requests: storage: 10Gi ``` Let's create persistent volume claim using above template. ```bash $ kubectl create -f test-pvc.yml persistentvolumeclaim "test-pvc" created ``` After creating the persistent volume claim, our persistent volume will change from `available` state to `bound` state. ```bash $ kubectl get pv NAME CAPACITY ACCESSMODES RECLAIMPOLICY STATUS CLAIM REASON AGE test-pv 10Gi RWX Retain Bound default/test-pvc 2m $kubectl get pvc NAME STATUS VOLUME CAPACITY ACCESSMODES AGE test-pvc Bound test-pv 10Gi RWX 1m ``` Now we have persistent volume claim available on our Kubernetes cluster, Let's use it in deployment. ### Deploying Kubernetes application We will use following deployment template as `test-pv-deployment.yml`. ```yaml apiVersion: extensions/v1beta1 kind: Deployment metadata: name: test-pv labels: app: test-pv spec: replicas: 1 template: metadata: labels: app: test-pv tier: frontend spec: containers: - image: /:latest name: test-pv imagePullPolicy: Always env: - name: APP_ENV value: staging - name: UNICORN_WORKER_PROCESSES value: "2" volumeMounts: - name: test-volume mountPath: "//shared/data" ports: - containerPort: 80 imagePullSecrets: - name: registrypullsecret volumes: - name: test-volume persistentVolumeClaim: claimName: test-pvc ``` Now launch the deployment using following command. ```bash $ kubectl create -f test-pvc.yml deployment "test-pv" created ``` Once the deployment is up and running all the contents on `shared` directory will be stored on persistent volume claim. Further when pod or deployment crashes for any reason our data will be always retained on the persistent volume. We can use it to launch the application deployment. This solved our goal of retaining data across deployments across `pod` restarts. ## Links - [Human page](https://www.bigbinary.com/blog/using-kubernetes-persistent-volume-for-persistent-data-storage)