=============
Kubernetes
==============

=> Open source orchestration platform

=> K8S is used to manage our containers

=> K8S provided a framework to handle containers related tasks
	(deployment, scaling, load balancing etc....)

=> K8S developed by Google and donated to CNCF

===============
K8S Advantages
===============

1) Container Orchestration

2) Auto Scaling

3) Self Healing

4) Load Balancing

==================
K8S Architecture
==================

=> K8S will follow cluster architecture (group of servers)

		=> Master Node / Control Plane
		=> Woker Nodes

=> K8S control plane will contain below components

	1) API Server
	2) Schedular
	3) Controller Manager
	4) ETCD

=> K8S worker node will container below components

	1) POD
	2) Containers
	3) Docker Engine
	4) Kublet
	5) Kube Proxy

=> To communicate with K8S control plane we have 2 options

	1) UI (Web Dashboard)

	2) Kubectl (CLI)


==============================
K8S Architecture Components
==============================

=> API Server will recieve incoming requests and it will store into ETCD.

=> ETCD is k8s cluster database

=> Schedular will check pending tasks in ETCD and it will schedule those task in worker nodes.

=> Schedular will get available workers nodes information by using kubelet.

=> Kubelet is called as Worker node agent.

=> Kube-Proxy provides network for cluster communication

=> POD is a smallet building block that we run in kubernetes cluster. POD represents runtime instance of our application.

Note: In k8s, our project  will be excuted as a POD. Inside POD containers will be created.

=> Controller-Manager will monitor all k8s resources functionality.



### EKS Cluster Setup DOC : https://github.com/ashokitschool/DevOps-Documents/blob/main/EKS-Setup.md

===================================
Kubernete Cluster Core Components
===================================

1) Control Plane

	1.1) API Server
	1.2) Schedular
	1.3) Controller - Manager
	1.4) ETCD

2) Worker Node

	2.1) Kubelet
	2.2) Kube-Proxy
	2.3) Docker Engine
	2.4) Container
	2.5) POD


============
What is POD
============

=> POD is a smallest building block that we can deploy in k8s cluster

=> Our application will be deployed in k8s cluster as a POD only

=> For one application we can create multiple POD replicas for high availability

=> For every POD one IP address will be generated.

=> If POD got damaged/crashed then K8S will replace it (Self-healing)

=> To create PODS we will use MANIFEST YML files

Note: By default PODS are accessible only with in the cluster (we can't access outside)

=> To expose PODS for outside access we need to use K8S services concept.

==========================
What is Service in K8S ?
==========================

=> K8S service is used to expose PODS

=> We have 3 types of services

1) Cluster IP (To access PODS with in the cluster)

2) Node Port (To access PODS using NODE Public IP)

3) Load Balancer (To distribute the traffic to pod replicas)

=========================
K8S Manifest YML syntax
=========================
---
apiVersion: apps/v1
kind: Deployment
metadata:
 name: javawebappdeployment
spec:
 replicas: 2
 strategy:
 	type: RollingUpdate
 selector:
 	matchLabels:
 	 app: javawebap
 template:
  metadata:
   name: javawebapppod
   labels:
    app: javawebapp
  spec:
   containers:
   - name: javawebappcontainer
     image: ashokit/javawebapp
     ports:
      - containerPort: 8080
---
apiVersion: v1
kind: Service
metadata:
 name: javawebappsvc
spec:
 type: LoadBalancer
 selector:
  app: javawebapp
 ports:
 - port: 80
   containerPort: 8080
...


# check pods running
$ kubectl get pods

# check pods running in which worker node
$ kubectl get pods -o wide

# check services created
$ kubectl get svc

# check deployments created
$ kubectl get deployment

# Execute k8s manifest yml
$ kubectl apply -f <yml>

# Check pod logs
$ kubectl logs <pod-name>

# Delete pod
$ kubectl delete pod <pod-name>

# delete resources we have created
$ kubectl delete all --all


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Docker Playlist : https://www.youtube.com/watch?v=8dccz7ca4FM&list=PLpLBSl8eY8jQ0lp6FeOtObvkfOddJW6YM

EFK Stack Setup in K8S : https://www.youtube.com/watch?v=8MLcbbfEL1U

HPA in K8S : https://www.youtube.com/watch?v=c-tsJrcB50I

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