Volumes,Persistent Volumes and PVC

Question 1

What are volumes ?

Answer 1

when a container restarts the state of application is reset. To keep some state we require volume concept .
Also when sharing files between two containers in a POD , we use volumes

ex:- awsElasticBlockStore ; azureDisk ;
configMap (after u create a confiMap object , you can use configMap type in POD to consume the configuration inside a container )

Question 2

what is persistent volume ?

Answer 2

PersistentVolume (PV) is a piece of storage in the cluster that has been provisioned by an administrator or dynamically provisioned using Storage Classes

Question 3

persistent volume claim - volume type

Answer 3

A persistentVolumeClaim volume is used to mount a PersistentVolume into a Pod. PersistentVolumeClaims are a way for users to “claim” durable storage (such as a GCE PersistentDisk or an iSCSI volume) without knowing the details of the particular cloud environment.

Question 4

what is persistent volume claim ?

Answer 4

PersistentVolumeClaim (PVC) is a request for storage by a user

Question 5

secret volume

Answer 5

A secret volume is used to pass sensitive information, such as passwords, to Pods. You can store secrets in the Kubernetes API and mount them as files for use by Pods without coupling to Kubernetes directly. secret volumes are backed by tmpfs (a RAM-backed filesystem) so they are never written to non-volatile storage

Question 6

imperative commands for pv, pvc

Answer 6

$ alias k=kubectl
$ k create -f pv.yaml [if declarative
$ k get pv , pvc

Question 7

declarative

persistent volumes

Answer 7

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv0003
spec:
  capacity:
    storage: 5Gi
  volumeMode: Filesystem
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Recycle
  mountOptions:
    - hard
    - nfsvers=4.1
  nfs:
    path: /tmp
    server: 172.17.0.2

Question 8

persitent volume claims ? write declarative

Answer 8

• every persistentvolumeclaim binds to one persistentvolume
• you can also customize to bind to a particular PersistentVolume by using labels and selectors
  also
• claimRef tag is used on PV to bind to PVC , volumeName can be used to bing PVC to PV

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: myclaim
spec:
 accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 3Gi

…

Question 9

how to check if persistent volume is there on pod or not

Answer 9

$ kubectl describe po pod-name

and check for Volumes: in it

Question 10

check the logs in a container
POD: webapp
log path : /log/app.log

Answer 10

$ kubectl exec -it webapp – cat /log/app.log

Question 11

volumeMount Vs volumes field

Answer 11

volumeMounts:
- mountPath: /var/log

it is the path inside a container where you want to mount a volume

volumes:

• name: vol-log
  hostpath:
  path: /log/app

volumes ( 23+ types )
different types of volumes are present .
for example hostpath is the path from underlying host (node) which can be mounted to a container

Question 12

create PV for hostpath

path: /app/log
storage: 5Gi

Answer 12

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv0003
spec:
  capacity:
    storage: 5Gi
  volumeMode: Filesystem
  accessModes:
    - ReadWriteMany
  hostpath:
    path: /var/log

Question 13

when access modes differ for Persistent volume and Persistent volume claim , does pvc bind to pv

Answer 13

NO

Question 14

when does a PVC get stuck in TERMINATING state

Answer 14

when the PVC is being used by a POD