---
title: " Scaling Stateful Applications using Kubernetes Pet Sets and FlexVolumes with Datera Elastic Data Fabric "
date: 2016-08-29
slug: stateful-applications-using-kubernetes-datera
url: /blog/2016/08/Stateful-Applications-Using-Kubernetes-Datera
author: >
  Shailesh Mittal (Datera Inc),
  Ashok Rajagopala (Datera Inc)
---

**Introduction**  

Persistent volumes in Kubernetes are foundational as customers move beyond stateless workloads to run stateful applications. While Kubernetes has supported stateful applications such as MySQL, Kafka, Cassandra, and Couchbase for a while, the introduction of Pet Sets has significantly improved this support. In particular, the procedure to sequence the provisioning and startup, the ability to scale and associate durably by [Pet Sets](/docs/user-guide/petset/) has provided the ability to automate to scale the “Pets” (applications that require consistent handling and durable placement).   

Datera, elastic block storage for cloud deployments, has [seamlessly integrated with Kubernetes](http://datera.io/blog-library/8/19/datera-simplifies-stateful-containers-on-kubernetes-13) through the [FlexVolume](/docs/user-guide/volumes/#flexvolume) framework. Based on the first principles of containers, Datera allows application resource provisioning to be decoupled from the underlying physical infrastructure. This brings clean contracts (aka, no dependency or direct knowledge of the underlying physical infrastructure), declarative formats, and eventually portability to stateful applications.  

While Kubernetes allows for great flexibility to define the underlying application infrastructure through yaml configurations, Datera allows for that configuration to be passed to the storage infrastructure to provide persistence. Through the notion of Datera AppTemplates, in a Kubernetes environment, stateful applications can be automated to scale.   





**Deploying Persistent Storage**



Persistent storage is defined using the Kubernetes [PersistentVolume](/docs/user-guide/persistent-volumes/#persistent-volumes) subsystem. PersistentVolumes are volume plugins and define volumes that live independently of the lifecycle of the pod that is using it. They are implemented as NFS, iSCSI, or by cloud provider specific storage system. Datera has developed a volume plugin for PersistentVolumes that can provision iSCSI block storage on the Datera Data Fabric for Kubernetes pods.



The Datera volume plugin gets invoked by kubelets on minion nodes and relays the calls to the Datera Data Fabric over its REST API. Below is a sample deployment of a PersistentVolume with the Datera plugin:



 ```
  apiVersion: v1

  kind: PersistentVolume

  metadata:

    name: pv-datera-0

  spec:

    capacity:

      storage: 100Gi

    accessModes:

      - ReadWriteOnce

    persistentVolumeReclaimPolicy: Retain

    flexVolume:

      driver: "datera/iscsi"

      fsType: "xfs"

      options:

        volumeID: "kube-pv-datera-0"

        size: “100"

        replica: "3"

        backstoreServer: "[tlx170.tlx.daterainc.com](http://tlx170.tlx.daterainc.com/):7717”
  ```



This manifest defines a PersistentVolume of 100 GB to be provisioned in the Datera Data Fabric, should a pod request the persistent storage.




 ```
[root@tlx241 /]# kubectl get pv

NAME          CAPACITY   ACCESSMODES   STATUS      CLAIM     REASON    AGE

pv-datera-0   100Gi        RWO         Available                       8s

pv-datera-1   100Gi        RWO         Available                       2s

pv-datera-2   100Gi        RWO         Available                       7s

pv-datera-3   100Gi        RWO         Available                       4s
  ```



**Configuration**



The Datera PersistenceVolume plugin is installed on all minion nodes. When a pod lands on a minion node with a valid claim bound to the persistent storage provisioned earlier, the Datera plugin forwards the request to create the volume on the Datera Data Fabric. All the options that are specified in the PersistentVolume manifest are sent to the plugin upon the provisioning request.