/Kubernetes-Notes

Kubernetes

What is Kubernetes

Kubernetes is an open-source container management also known as container orchestration tool for automating software deployment, scaling, and management.

What is Container Orchestration

Orchestration enables developers to easily build containerized applications and services, as well as scale, schedule and monitor those containers.

Nodes

Nodes are physical or virtual machine in which kubernetes is installed.

Cluster

Cluster is group of nodes, if one node fails we have our application accessible from other nodes.

Master

Master is other node in which kubernetes is installed and it manages other nodes

Components

  • API Server
  • etcd
  • kubelet
  • Container Runtime
  • Controller
  • Scheduler

Master V/S Worker node

Master has kube-apiserver installed and nodes have kubelet installed (Kubelet is an agent which make sure nodes are healthy) which provides information to master which stores information in etcd (key value storage)

Minikube

Minikube is a lightweight Kubernetes implementation that creates a VM on your local machine and deploys a simple cluster containing only one node.

  • Download kubectl and minikube to start using minikube

PODS

A Pod is a group of one or more containers, with shared storage and network resources, and a specification for how to run the containers.

Replication Controllers

Replication Controller used for high availability, it ensures that a specified number of pod replicas are running at any one time. It also helps load balancing and scaling when demand increases.

ReplicaSets replaced replication controllers. A ReplicaSet's purpose is to maintain a stable set of replica Pods running at any given time.

Deployments and Updates

Create Deloyment

kubectl create -f deployment.yml

Get Deloyment

kubectl get deployments

Update Deloyment

kubectl set image deployment/fitness-app mysql=mysql:8.0

Status of Deloyment

kubectl rollout status deployment/fitness-app

kubectl rollout history deployment/fitness-app

Rollback Deloyment

kubectl rollout undo deployment/fitness-app

Kubernetes Commands

kubectl

Kubectl is a Command line tool for communicating with a Kubernetes cluster.

Kubernetes version running on nodes

kubectl version

Number of nodes

kubectl get nodes

Command to create a pod and deploy docker container in PODs

kubectl run mysql --image mysql

List of PODS in Cluster

kubectl get pods

Get information about POD

kubectl describe pod mysql

Additional Information about POD

kubectl get pods -o wide

Create POD using pod-definition.yml file

kubectl create -f pod-definition.yml

Delete Pod

kubectl delete pod pod-name

Edit Pod

kubectl edit pod pod-name

pod-definition.yml

Kubernetes uses yml file as an input to create pods, replicas, deployments, services and so on,

The yml files contain four top level fields-

  • apiVersion: Depending on what we need to create use apiVersion, for creating pods use version v1
  • kind: Type of object we want to create such as Pod
  • metadata: Data about the object like name, labels and app.
  • spec: Specification

Create replica sets

kubectl create -f replicaset.yml

Get replica sets

kubectl get replicaset

Delete replica sets

kubectl delete replicaset replicaset-name

Replace replica sets

kubectl replace -f replicaset.yml

Scale replica sets

kubectl scale -replicas=6 -f replicaset.yml