CKA Reloading

Question 1

What are the components of a control plane?

Answer 1

MASTER:
ETCD (Key-Value store)
kube-scheduler (identify the right node to place the pod on), controllers (node-controller, replication-controller, controller-manager)
kube-apiserver (primary management component - orchestrates all operations within the cluster)

WORKER:
container run-time engine (e.g. docker, rkt, containerd)
kubelet (captain - runs on each node, listens for instructions from kube-apiserver, creates the pod on the node)
kubeproxy (communication between worker nodes are enabled by this service)

Question 2

How does kubernetes support other container run times e.g. rkt, containerd?

Answer 2

CRI (Container Runtime Interface) and should follow OCI standards (Open Container Initiative) - imagespec, runtimespec

dockershim (to still support docker) - REMOVED as containerd (deamon) supports CRI

Question 3

How is the information stored in a key-value store

Answer 3

In form of documents/pages. Each individual entry gets a document. Changes to one file does not affect the others. Dataformats: json or yaml

Question 4

What information is stored in etcd

Answer 4

Nodes
PODS
Configs
Secrets
Accounts
Roles
Bindings
Others

Question 5

How does kubeadm deploy a kubernetes cluster control plane components?

Answer 5

As pods in kube-system namespace. you can check using

kubectl get pods -n kube-system

Question 6

What happens when I type kubectl get nodes. Explain the workflow.

Answer 6

The kube-apiserver authenticates the request and validates it
The data is then retrieved from etcd cluster and responds back

Question 7

Explain the workflow for a pod creation

Answer 7

The kube-apiserver updates the information in etcd cluster
updates user that a pod is created
kube-scheduler continuously monitors the apiserver and realizes there is a pod with no node assigned
scheduler identifies the right node to put the pod on and communicates back to the kube-apiserver
kube-apiserver then updates the information in etcd cluster
apiserver then passes the information to kubelet in the appropriate worker node
kubelet then creates the pod and instructs the container-engine to deploy the application image
Once done, kubelet updates the status back to the apiserver which in turn updates the data back in etcd cluster

kube-apiserver is the only component that interacts directly with the etcd data store

1. Authenticate User
2. Validate Request
3. Retrieve data
4. Update ETCD
5. Scheduler
6. Kubelet

Question 8

What does kube-controller manager do?

Answer 8

Watch status e.g. every 5 secs for nodes
Remediate Situation

e.g. Node controller, replication controller (ensures desired no. of pods are present)

Question 9

Which folder has all the config files for control plane components deployed using kubeadm

Answer 9

cat /etc/kubernetes/manifests/kube-controller-manager.yaml

cat /etc/kubernetes/manifests/kube-scheduler.yaml

Question 10

What does kubelet do?

Answer 10

Registers the node with the kubernetes cluster
Create PODs
Requests container-engine to deploy the application in the POD
Monitor Mode & PODs and reports to kube-apiserver

KUBEADM does not deploy kubelet.. It should be manually installed

Question 11

When is a service created?

Answer 11

To expose an application to other PODs. The other PODs can access the application using the name of the service. The service also gets an IP.

Service does not join the POD network.

Enable loose coupling between microservices application

Question 12

What does kubeproxy do?

Answer 12

Runs on each node in the kubernetes cluster. It looks for new services and creates appropriate rules on each node to forward traffic to the POD using iptables rules

Single POD is always deployed on each node in the cluster (deployed as deamonset - e.g. logging)

Question 13

What is a POD?

Answer 13

A single instance of an application. Containers are encapsulated in PODs

Question 14

How to deploy a POD using kubectl?

Answer 14

kubectl run pod_name –image image_name

This command deploys a docker container by creating a POD

Question 15

How to see a list of pods available?

Answer 15

kubectl get pods

Question 16

How to create a POD using POD definition file?

Answer 16

apiVersion: v1
kind: Pod
metadata:
name: mypod
labels:
type: front_end
spec:
containers:
- name: mycontainer
image: nginx

kubectl create -f 1.yaml or kubectl apply -f 1.yaml

create and apply works the same way if you are creating a new object

Question 17

What is the apiVersion for POD, Service, ReplicaSet & Deployment?

Answer 17

POD: v1
Service: v1
ReplicaSet: apps/v1
Deployment: apps/v1

Question 18

How to see detailed information of the POD

Answer 18

kubectl describe pod pod_name

Question 19

How to create a replicaset using pod definition file

Answer 19

apiVersion: apps/v1
kind: ReplicaSet
metadata:
name: myreplicaset
labels:
type: front_end
spec:
replicas: 2
selector:
matchLabels:
type: front_end
template:
metadata:
labels:
type: front_end
spec:
containers:
- name: mycontainer
image: nginx

Question 20

What is the purpose of selector in replicaset?

Answer 20

It helps identify what pods fall under it. Replicaset can also manage pods that are not created as part of replicaset creation.

selector:
matchLabels:
type: front_end

Question 21

How to scale a replicaset?

Answer 21

Option 1: Update the definition file and then run k replace -f replicaset-definition.yaml

Option 2: k scale –replicas=6 -f replicaset-definition.yaml (DOES NOT CHANGE THE FILE)

OR

k scale –replicas=6 replicaset replicaset_name

Question 22

If you have an object and want to extract the pod definition file of that object how to do that?

Answer 22

e.g. k get replicaset replica_set_name -o yaml > definition_file.yaml

If the object does not pre-exist
kubectl create replicaset <replicaset-name> --image=<image-name> --dry-run=client -o yaml > replicaset-definition.yaml</image-name></replicaset-name>

Question 23

What is the purpose of deployments?

Answer 23

For managing updates to the infrastructure e..g rollingupdates, or rollback

Question 24

How to create a deployment?

Answer 24

apiVersion: apps/v1
kind: Deployment
metadata:
name: mydeployment
labels:
type: front_end
spec:
replicas: 2
selector:
matchLabels:
type: front_end
template:
metadata:
labels:
type: front_end
spec:
containers:
- name: mycontainer
image: nginx

Question 25

Types of deployment strategies

Answer 25

RollingUpdate (default)
Recreate

Question 26

How to see the status of rollout for a deployment?

Answer 26

k rollout status deployment/deployment_name

Question 27

How to see the revisions of rollout for a deployment?

Answer 27

k rollout history deployment/deployment_name

Question 28

How to apply any definition file changes?

Answer 28

k apply -f deployment-definition.yaml

If you are changing image then you can do it by using set image command

k set image deployment/deployment_name container_name=image_name (FILE NOT CHANGED)

Question 29

How to undo a rollout?

Answer 29

k rollout undo deployment/deployment_name

Question 30

How to record the cause of change in a deployment

Answer 30

k create -f deployment_file.yaml –record

Question 31

What does k edit command do

Answer 31

It will open the definition file and you can make edits to it. Once changes are done, the updates will take place

Question 32

What are the types of services

Answer 32

NodePort (external access) - maps a port on the node to a port on the pod
ClusterIP (within the cluster)
LoadBalancer

Question 33

What are the different ports in nodePort

Answer 33

TargetPort (pod)
Port (service) - mandatory
nodePort (node’s port) - 30000 - 32767

Question 34

How to create a service?

Answer 34

apiVersion: v1
kind: Service
metadata:
name: myservice
labels:
type: front_end
spec:
ports:
- port: 80
targetPort: 80
nodePort: 30008
selector:
type: front_end (selects all pods that match this label as endpoints to forward the traffic)
type: NodePort

Question 35

What are the 3 namespaces created by default in kubernetes

Answer 35

Default
kube-system
kube-public