If you have ever worked with Containers such as Dockers, you know how efficient and fast they are.

Kubernetes is a container-orchestrator that automated the deployments and shutdown instances to make them highly available and elastic to respond to the demand flotation.

Everything starts with a Cluster. It is the “pool” that contains N “resources”, called Nodes.

The first node is the “master” and manager the workload on the other nodes, called “workers”.

The Pods (that contain the containers with the application) are distributed among the nodes for better performance.

Kubernetes can scale up and down the number of nodes based on the parameters set such as CPU or RAM usage, which would indicate the physical resources are not sufficient or they are idle.

Installing Kubernetes

curl -LO https://storage.googleapis.com/kubernetes-release/release/$(curl -s https://storage.googleapis.com/kubernetes-release/release/stable.txt)/bin/linux/amd64/kubectl
chmod +x ./kubectl
sudo mv ./kubectl /usr/local/bin/kubectl

Download the configuration file from your Kubernetes server and define a variable to it (place it in a safe place and appropriate permissions):

export KUBECONFIG=kube1-kubeconfig.yaml

Commands list that can be used to manage the cluster:

kubectl --help
kubectl get nodes
kubectl cluster-info

Example of a simple manual deployment of a container:

kubectl run nginx-api --image=nginx --port=80
kubectl get pods
kubectl describe pods
kubectl delete pods nginx-api

Getting a Shell into the Container

kubectl exec --stdin --tty nginx-api-***********-**** -- bash

OR

kubectl exec -it nginx-api-***********-**** -- bash

Automating Deployments

Create the deployments.yaml using the template (indentation must be respected):

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx-instance
spec:
  replicas: 6
  selector:
    matchLabels:
      app: nginx-instance
  template:
    metadata:
      labels:
        app: nginx-instance
    spec:
      containers:
      - name: nginx-instance
        image: nginx
        imagePullPolicy: Always
        ports:
        - containerPort: 80
kubectl apply -f nginx-deployment.yaml

Editing the deployment configuration:

kubectl edit deployment nginx-deployment
kubectl get pods -o wide

Load Balancer

Create a file called loadbalancer.yaml like the example:

apiVersion: v1
kind: Service
metadata:
  name: nginx-loadbalancer
  annotations:
    service.beta.kubernetes.io/linode-loadbalancer-throttle: "5"
  labels:
    app: nginx-loadbalancer
spec:
  type: LoadBalancer
  selector:
    app: nginx-instance
  ports:
    - name: http
      protocol: TCP
      port: 80
      targetPort: 80
  sessionAffinity: None
kubectl apply -f loadbalancer.yaml
kubectl get services
kubectl describe service nginx-loadbalancer

Port-Forwarding

kubectl port-forward app-********-***** 8080:80
kubectl port-forward pods/app-********-***** 8080:80
kubectl port-forward deployment/app 8080:80
kubectl port-forward replicaset/app-******** 8080:80
kubectl port-forward service/app 8080:80

Now NGINX is accessible externally through the load balancer service!

Other useful commands:

kubectl get pods -w
kubectl get all
kubectl scale deploy/nginx --replicas=3
kubectl rollout status deploy/nginx
kubectl rollout undo deploy/nginx
kubectl deploy nginx --image=nginx:1.17-alpine -o yaml --dry-run=client
kubectl explain services

SEE ALSO

Kubernetes Persistent Volumes [Link].

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