Sun Sep 17

In Kubernetes it is possible to maintain persistent data

• The core concepts are:

  1. volume classes (vc)
  2. persistent volumes (pv) based on vc
  3. persistent volume claims(pvc) based onpvc.podspecs that specify volumes based onpvc`
  4. containerspecs (within pod specs) that specifyvolumeMountsbased onpodvolumes``

• So each of these is based upon the former until vc hits the raw layer of whatever the kubernetes is hosted upon.

• Since Kubernetes 1.6 it has been possible to create pvcs directly without needing to first create pvs. This is referred to as dynamic provisioning. link

• More about the concept can be read on the storage docs. The third sub-section just links to a blog post, so incomplete?

• A blog post going over the topic in an end-to-end example can be found here

• Another example is [one section on the k8s task-oriented docs

• Example:

  ❯ kc get pv
  NAME CAPACITY ACCESSMODES RECLAIMPOLICY STATUS CLAIM STORAGECLASS REASON AGE
  pvc-46c2c0df-9c19-11e7-a0d1-0800271d32bc 1Gi RWO Delete Bound default/mypvc standard 47m
  
  ❯ kc get pvc
  NAME STATUS VOLUME CAPACITY ACCESSMODES STORAGECLASS AGE
  mypvc Bound pvc-46c2c0df-9c19-11e7-a0d1-0800271d32bc 1Gi RWO standard 47m
  
  ❯ cat ./deployment.yaml
  apiVersion: apps/v1beta1
  kind: Deployment
  metadata:
  name: dgraph
  labels:
  app: dgraph
  spec: # ReplicaSet
  replicas: 1
  template: # Pod
  metadata:
  labels:
  app: dgraph
  spec:
  volumes: - name: dgraph
  persistentVolumeClaim:
  claimName: mypvc
  containers: - name: dgraph
  image: dgraph/dgraph:latest
  ports: - name: ui
  containerPort: 8080 - name: client
  containerPort: 9080
  command: - dgraph
  args: - -bindall=true - -memory_mb=2048
  volumeMounts: - name: dgraph
  mountPath: /dgraph