Storage Solutions in K8s

• Stateful applications store data locally. In Containers the data created locally will be lost once you delete it. So to solve this in docker we have used volumes. Volumes have a lifecycle which has no relation to container lifecycle (refer docker containers, image layers, volumes)
• IN k8s we are running docker containers, k8s is an orchestration solutions.
• Lets see what are options for storage provisioning in k8s Refer Here
• The most widely used storage types
  • Volumes
  • Persistent Volumes
    • Storage Classes
    • Persistent Volume Claims
• Volumes Refer Here

Volumes

• Volumes can be mounted to containers and they have lifetime equivalent to Pods.
• The types of Volumes Refer Here
• The types
  • storage on cloud
    • ebs
    • azure disk
    • efs
    • azure file
    • gcs
  • empty dir
  • hostPath
• Lets create a manifest with mysql-pod with volume

---
apiVersion: v1
kind: Pod
metadata:
  name: mysql-vol
  labels:
    app: mysql
    layer: db
spec:
  containers:
    - name: mysql
      image: mysql:8
      ports:
        - containerPort: 3306
      volumeMounts:
        - name: test-volume
          mountPath: /var/lib/mysql
  volumes:
    - name: test-volume
      emptyDir:
        sizeLimit: 100Mi

Persistent Volumes

• These volumes will have a lifetime different than Pod i.e. they exist even after pod is dead.
• Types of PVC Refer Here
• Persistent Volumes in Azure Refer Here
• Storage classes in Azure Refer Here
• Storage classes in AWS Refer Here

Lets create a mysql-pod with dynamic volume provisioing

• Get storage classes
  
• Lets create a Persistent Volume Claim and a mysql pod claiming pvc
  
• Refer Here for the initial manifests written by us
• Now lets modify the spec to add mysql related environment variables
  
• Refer Here for the mysql env values
• INsert some data into mysql
  
• now delete pod and recreate and check for the data created
  
• For static provisioning of volume Refer Here
• If you want to scale Pods we can use
  • Replica Sets
  • Deployments
    

StatefulSets

• Statefulset is like deployment with replicas. But each pod gets its own volume.
• Stateful Set is for stateful applications
  
• When we create replicas in Stateful Set we get predictable names
• Refer Here for official docs
• We can access individual pod, by creating headless service and by using ...svc.cluster.local
• Lets experiment with stateful sets and create nginx pods
• Refer Here for the manifests
  
• Naming is predictable in stateful sets
  
• Now create a different html page for every pod
  
• Send a curl request from any alpine pod <pod-name>.<headless.svc-name>.<namespace>.svc.cluster.local
  
  

Kuberentes namespace

• Refer Here for official docs