Kubernetes CKA Class First class

#kubernetes-cka

Create a namespaces

To get all namespaces and manage it follow the steps

kubectl  get namespaces
kubectl create namespace  bakulya

Node

To get all nodes and see on yaml versions follow the steps. If you would like to get json version just change yaml to json.

kubectl get nodes
kubectl get nodes fs-secondnode
kubectl get nodes fs-secondnode -o yaml

Run the pods or create a pod.

Pods are groups of containers. We will create a pod and get to inside the pods (container)

kubectl get pods
kubectl run -i -t centos --image=centos

Log in to the pod

In this example we log out from pod and then log in back to pods.

exit
kubectl get pods # to get name of the pod
kubectl attach -i -t centos-7474788896-gt78z

Understanding the ephemeral on pod(containers)

Whenever you log in to pod or container if you create or modified something. It will deleted and reverted back by default version. Example follow the steps

kubectl get pods
kubectl attach -i -t centos-7474788896-gt78z
yum install net-tools -y
ifconfig
exit
# when ever we exit kubernteds will recreate the pod
kubectl attach -i -t centos-7474788896-gt78z
ifconfig # result bash: ifconfig: command not found

Get list of pods and log in to pod then install the net tools. Make sure ifconfig is installed and exited Log in back to the pod and try to run ifconfig

Create pod from yaml file.

We will create a pod call centos from yaml file. Example file looks like this

apiVersion: v1
kind: Pod
metadata:
  labels:
    run: centos
  name: centos-pod
spec:
  containers:
  - image: centos
    name: centos
    stdin: true
    tty: true

Now we can create a pod running command kubectl apply -f centos.yaml

Scheduling the pods per nodes

In this example we will create a pod on one of our nodes. Our pod will run on node fs-node

apiVersion: v1
kind: Pod
metadata:
  labels:
    run: centos
  name: centos-pod
spec:
  nodeSelector:
    kubernetes.io/hostname: fs-node
  containers:
  - image: centos
    name: centos
    stdin: true
    tty: true

We will create test pod from google

We will use kuard image from google. This image created for testing purposes and this image will exposed to the maters external ip. This example file for kuard

apiVersion: v1
kind: Pod
metadata:
  labels:
    app: kuard
  name: kuard
spec:
  containers:
  - image: gcr.io/kuar-demo/kuard-amd64:1
    name: kuard
    ports:
    - containerPort: 8080
      name: http
      protocol: TCP

Create pod kubectl apply -f kuard.yaml

Exapose pods port to Master ip(Cluster-ip) kubectl expose pod kuard --type=ClusterIP --external-ip=165.227.67.15

DemonSet on Kubernetes

Demon Set is one the resource type on the kubernetes. Which will crated exactly copy of the resource each nodes.

Requests resource from kubernetes

On kubernetes you can reserve a resource. Let say I have application which should take more than 128M ram. I can reserve that resource from the cluster. example yaml looks like this.

apiVersion: v1
kind: Pod
metadata:
  labels:
    app: myapp
  name: myapp
spec:
  containers:
  - image: gcr.io/kuar-demo/kuard-amd64:1
    name: kuard
    resources:
      requests:
        cpu: "100m"
        memory: "128Mi"
      limits:
        cpu: "200m"
        memory: "256Mi"
    ports:
    - containerPort: 8080
      name: http
      protocol: TCP