====================
Kuberetes Software
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=> Docker is a containerization s/w

=> Docker is free & open source

=> Using Docker we will package our "application code + application dependencies" as single unit for execution. That is called as Docker image.

=> Once docker image is created then we can run that image in any machine without bothering about underlying softwares.

Note: Docker will take care of s/w installation which are required to run our application.

=> Docker is used to run our app in any machine

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Kubernetes
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=> It is free and open source s/w

=> K8S developed by google company

Note: Orchestration means management.

=> K8s is called as Orchestration s/w

=> K8S is used to manage docker containers.

Ex : create , stop, start , delete, scale up, scale down...


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K8S Advantages
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1) Orchestration : Manage containers

2) Self Healing : If container damanged then it will create new one.

3) Load Balancing : Distribute requests to all running containers

4) Auto Scaling : Scale up and scale down containers on demand basis.

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K8S Architecture
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1) kubectl
2) Control Plane
3) Worker Nodes


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K8S Cluster Setup
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1) Self Managed Cluster (we are responsible for everything)

	a) MiniKube (single node) --> only for learning/practice

	b) Kubeadm (Multi Node) --> We have to setup

2) Provider Managed Cluster (ready made cluster)

	a) AWS EKS (Elastic K8S Service)

	b) Azure AKS (Azure K8s Service)

	c) GCP GKE	(Google K8S Engine)

Note: Provider Managed clusters are commercial.

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AWS EKS Setup
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@@ Git Repo : https://github.com/ashokitschool/DevOps-Documents/blob/main/05-EKS-Setup.md

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K8S Terminology
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1) PODS
2) Services
3) Namespaces
4) Deployment

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What is POD ?
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=> POD is a smallest building block that will be created in k8s cluster.

=> In k8s, everything will be represented/managed as a POD only.

=> Inside POD, container will be created.

=> POD is accessible only with in the cluster.

=> To access our application which is running inside the POD then we have to expose the PODS.

=> To expose PODS we will use k8s services.

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K8S Services
==============

=> In k8s we have 3 types of services.

		1) ClusterIP
		2) NodePort
		3) LoadBalancer

=> ClusterIP is used to map all pods to single IP to access with in cluster.

=> To expose the pods outside cluster we can use NodePort service.

Note: When we use NodePort service we can access PODS which are running in particular worker node only.

=> If we want to access all the pods running in all worker nodes then we will expose pods using LoadBalancer service.

Note: When we use LoadBalancer, internally EKS will create AWS LBR to access our pods outside of the cluster.

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What is Namespace ?
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=> Namespaces are equal to packages in java.

=> K8s namespaces are used to group k8s resources logically.

		database_pods ====> ashokit_db_ns
		
		backend_app_pods ====> ashokit_backend_ns

		frontend_app_pods ====> ashokit_frontend_ns

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What is Deployment
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=> Deployment is a k8s resource which is used to manage k8s pods lifecycle.

		a) create pods
		b) scale up
		c) scale down
		d) load balancing
		e) auto scaling