Some Back Story

Configuration Management

• This basically means you can maintain all the changes in your infrastructure with the help of a software
• e.g. Ansible etc
• Previously it was mutable ( like you can make the changes to your servers that were running) before virtual machines
• When VMs came they became immutable (You cannot change that is already running )
  • Therefore it offers some reliability as compared to before VMs scenerio
  • It is better in terms of security & stuff

Monolithic Applications

• Lets suppose we have a website which has Frontend, Backend, Chat messages, DB, Networking component
• In This example we have 5 components in a single webapp.
• If You bundle this as a single application
  • Here bundle means Deploying it as one application in the container
  • This is Known as Monolithic application
• Now The problem with monolithic application is that since it is deployed as a one complete bundle so suppose if you wanna make changes in DB you would have to deploy everything entirely , which is not a very good design to have

Present scenario

Micro-services

• We solved the problem of monolithic applications by implementing Microservices. Now basically the idea is that instead of deploying the whole app as a single application all of those components are deployed as individual applications
  • i.e. Frontend, Backend, DB, chat messaging , networking component are deployed separately
• We can use containers and run the microservices inside containers
• Fault isolation: You can make changes in one application without affecting the other applications

Orchestration

• Orchestrations help us in deploying and managing applications dynamically
• Kubernetes does orchestration
• Remember: Kubernetes is much more than a container orchestrator

Difference between Docker and Kubernetes

• Docker is a container tool and Kubernetes acts as an orchestrator

Architecture of Kubernetes

• It basically means that you have your own bunch of Nodes and Control Plane (i.e. Nodes + Control plane)
  • Node : Can be treated as a virtual machine
  • Control plane : Previously known as master node
• 

• It is the Command Line tool
• Kubectl communicates with the control plane
  • Like => hey control plane, I want to start 10 application. Control plane => Okay, let me see which which node is empty and can handle the load, I will redirect your containers over there

• It is a scheduling unit in K8s
• 

Steps for running applications in K8s

• i.e. Containerization

Control Plane

• API Server
  • All the Communication that will take place will happen via API server
• etcd
  • It's a Database, it basically stores information about the cluster
• Controller manager
  • It has 4 functionalities
    • 1) Check the desired state
    • 2) Manage the current state
    • 3) Differneces
    • 4) Make the changes
• Scheduler
  • It is responsible for physically scheduling the objects & stuffs

Inside Worker Node

• Kubelet is very important
• It's on every worker node
• So whenever new worker node is created and attached to the control plane the Kubelet is installed on them
• Its job is to listen to API server

• It is something that is responsible for networking
• If your cluster wants to communicate with outside world, kube-proxy will help in doing that
• Kube-proxy will make sure that every worker node & stuff that you have will get its own unique IP address

K8s DNS