Kubernetes Architecture

What is Kubernetes?

• Kubernetes is a portable, extensible, opensource platform for managing containerized workloads and services

Architecture:

• Components of kubernetes (k8s) cluster
  
• Control Plane Components
  • The control plane components make decissions about the cluster
  • Control plane can be run on any machine in the cluster
  • We can create a highly available cluster by using multiple machines for control plane components
  • The components are:
    • kube-apiserver
    • etcd
    • kube-scheduler
    • kube-controller-manager
    • kube-cloud-controller-manager
• Node Components:
• Thy run on every node, maintianing running pods and providing k8s runtime environment.
• Our applications will be running on nodes
• The Node Components are
  • kubelet
  • kube-proxy
  • Container runtime
• kube-apiserver:
  • The API server is a component of k8s control plane that exposes k8s API (Front-end of k8s)
  • All the communication between control plane and nodes is also handled by api server
  • To make k8s HA (highly Available), we can horizontal scale api-server
  • As a user of k8s cluster we can interact with kube-api server using API with json or a tool called a kubectl which is a command line tool
• etcd: Refer Here
  • This is distribute key-value store.
  • k8s uses etc to store all the cluster data
• kube-scheduler:
  • Control plane component that creates Pods on the nodes by selecting them
• kube-controller-manager:
  • Control plane component runs controller proceses. Each controller is a seperate process, but to reduce complexity they run in single process
  • Some major types of controller are
    • Node Controller: Responsible for noticing and responding when node goes down
    • Job Controller
    • Endpoints controller
• Cloud-controller-manager:
  • This component embeds cloud-specific logic
• Kubelet:
  • This is an agent that runs on each node in the cluster.
  • Kubelet recieves requests/orders to create new Pods
• kube-proxy:
  • This is a network proxy that runs on each node in k8s
  • This maintains network rules on the nodes
• Container runtime:
  • Kubernetes suppors container run times such as containerd, CRI-O and any implementation of Kubernetes CRI (Container Runtime instance)
• Basic Workflow
  
• Note: JSON and YAML Tutorial Refer Here