State Persistence - Volumes

Question 1

How can we specify a volume with Directory for data to be saved by a pod?

Answer 1

... 
kind: Pod
...
spec:
 containers:
 - image: ...
   volumeMounts:
	 - mountPath: /opt
	   name: data-volume
 volumes:
 - name: data-volume
   hostPath: 
	   path: /data
	  	type: Directoy

-> data volume is mounted on the path /opt on the container
-> therefore /opt is on the /data volume/Directory on the host

Question 2

What options do exist for volume types?

Answer 2

• data-volume: only useful with one node
• different third party solutions, like aws elastic block storage

Question 3

What is the downside of regular volumes in large environment?

Answer 3

• every pod definition file defines its volume
• changes would need to be made to all pods
• a more centralized approach can be preffered

Question 4

What is a persistent Volume?

Answer 4

• cluster-wide pool of storage volumes
• configured by an administrator
• to be used by users deploying applications on the cluster (via PVC)

Question 5

How do you define a persistent Volume?

Answer 5

apiVersion: v1
kind: PersistentVolume
metadata: 
  name: pv-voll
spec:
  accessModes:
	  - ReadWriteOnce (// ReadOnlyMany//ReadWriteMany)
	  capacity:
		  storage: 1Gi
		hostPath: (not to be used in production, replaced by third party solution)
		  path: /tmp/data
	persistentVolumeReclaimPolicy: Retain / Delete / Recycle

Question 6

What are Persistent Volumes and Persistent Volume claims?

Answer 6

• separate objects in Kubernetes namespace
• admin creates set of persistent volumes
• user creates persistent volume claims to use the storage
• once pvcs are created, Kubernetes binds them to PVs based on the request and properties set on the volume

Question 7

To how many PVs is a PVC bound?

Answer 7

• to only one

Question 8

What request characteristics define whether a PVC and a PV are bound together?

Answer 8

• sufficient capacity
• Access Modes
• Volume Modes
• Storage Class

Question 9

How can you select a specific type of PV, if all other characters match?

Answer 9

Using Selector and Labels

Question 10

What happens if only larger then the PVC PVs are available

Answer 10

• both are bound together
• the remaining capacity of the PV is not used
• 1 to 1 relationship between PV and PVC

Question 11

What happens if no fitting PV is available to a PVC

Answer 11

PVC remains in a pending state

Question 12

How do you define a persistent volume claim?

Answer 12

apiVersion:
kind: PersistentVolumeClaim
metadata:
  name: myclaim
spec:
  accessModes:
	  - ReadWriteOnce
	 resources:
	   requests:
		   storage: 500Mi

Question 13

What happens to a PersistentVolume once a Claim gets deleted?

Answer 13

• configurable by Reclaim policy
• by default: Retain -> will remain till manually deleted by the admin, not available for reuse by any other claims
• Delete: deletes the PVs automatically
• Recycle: data in Data volume will be scrubbed before making it available to other claims

Question 14

How can we use PVCs in pods?

Answer 14

pod.yaml
~~~
spec:
containers:
- name: myfrontend
image: nginx
volumeMounts:
- mountPath: “/var/www/html”
name: mypd
volumes:
- name: mypd
persistentVolumeClaim:
claimName: myclaim
~~~

Question 15

What volume Type is used to store data in a Pod only as long as that Pod is running on that node?

Answer 15

• emptyDir

Question 16

What happens when you delete a PVC that is used by a pod?

Answer 16

• it is stuck in Status Terminating