Optional - Storage Classes, StatefulSets

Question 1

What is Static Provisioning?

Answer 1

• when creating PVs/PVCs etc you define what volume (azure, aws) should be used
• before it can be used, it first must be manually provisioned, using the same name

Question 2

What are Storage Classes used for?

Answer 2

• used for dynamic provisioning underlying volume storage
• allows to define provisioners (like google storage) to dynamically provision storage on google cloud and attach that to pods when a claim is made

Question 3

How do you define a Storage Class?

Answer 3

sc-definition.yaml
~~~
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
name: google-storage
provisioner: kubernetes.io/gce-pd
~~~

Question 4

How are Storage Class yamls used?

Answer 4

• instead of PV.yaml
• in PVC.yaml:
  ~~~
  spec:
  accessModes:
  - ReadWriteOnce
  storageClassName: google-storage
  resources:
  requests:
  storage: 500 Mi
  ~~~

Question 5

How does dynamic provisioning work?

Answer 5

• when a new claim is created
• it uses the defined provisioner to provision a new disk with the required size
• then creates a persistent volume and then binds the pvc to that volume

Question 6

Why do we need Stateful Sets? Why are deployments not enough?

Answer 6

• are similiar to deployments sets
• create pods based on a template
• scale up/down
• perform updates and rollbacks

BUT:
- pods are created in a sequential order
- first pod must be running, before the next one is deployed
- assign unique ordinal index to each pod
- maintain a sticky identity for pods
- name schema: set-name + pod nr (1-x)
- pods perform a clone from the previous nr, (2 from 1, etc)

Question 7

How do you define a Stateful Set?

Answer 7

Like a Deployment but kind=StatefulSet und spec.serviceName (for the name of a headless service)

Question 8

Take a set of database pods, why can you not use a regular service to read and write?

Answer 8

• because the default Loadbalancer would split the writes and reads among all db-instances
• but we want writes to happen only on the db-master instance

Question 9

What is a headless Service? What does it do?

Answer 9

• created like a regular service
• but has no IP of its own
• does not perform any load balancing
• Creates DNS entries for each pod using the pod-name and a sub-domain

podname.headless-servicename.namespace.svc.cluster-domain.example

Question 10

How do we create a headless service?

Answer 10

apiVersion: v1
kind: Service
metadata: 
  name: mysql-h
spec:
  ports:
	 - port: 3306
	selector:
	  app: mysql
	clusterIP: None

clusterIP: None is new

Question 11

How do you point from a headless service to a pod?

Answer 11

• Pod definition yaml spec.subdomain needs to be the same as the name of the service

Question 12

How do you create a DNS record for a service to point to specific pods?

Answer 12

in Pod-yaml, beside spec.subdomain, add:
- hostname:

Question 13

What are Security Primitives?