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Kubernetes introduction and architecture

  • Kubernetes is container orchestrator making many servers act like one.
  • Kubernetes usually run's on top of docker but can use other container runtimes like containerd or crio
  • Kubernetes provides API/CLI to manage containers across servers
  • Similar to linux distributions there are kubernetes distributions as well

Advantages of Docker Swarm

  • Comes with docker, single vendor container platform
  • Easiest to deploy & manage
  • Can run anywhere docker does Eg: local, cloud, datacenter, ARM, windows 32-bit, 64-bit
  • Secure by default (mutual tls authentication in swarm, encrypted control plane & database secrets)
  • Easier to troubleshoot

Advantages of Kubernetes

  • Cloud/Infrastructure vendors will deploy/manage kubernetes
  • Wide adoption in the community
  • Flexible: cover a wide range of use cases

Kubernetes Terminology

Cluster - A deployment of kubernetes. It provides management, orchestration, healing & service access.

Node - Resources; Compute to run pods which are placed inside nodes

Pod - One or more containers; Smallest unit in kubernetes; often 1 container runs in 1 pod.

  • Kubernetes does not run containers directly, it runs pods (Containers encapsulated in pods)
  • Pod is the smallest unit of deployment in kubernetes
  • Pod is a single instance of an application
  • A single pod can have multiple containers but they are usually not multiple containers of the same application Eg: Healthcheck container, Helper container. However, this is a rare use case
  • Containers in a pod share the same IP address and port space (Can communicate with each other using localhost)

kubectl run nginx --image nginx
Service - Abstraction of pods. Service runs in one or more pods and provides access to containerized application.

Job - Ad-Hoc task. One or more pods are created for the job until completion.

Ingress - Exposes a external component to the service

Ingress Controller - Used to provide ingress (Eg: AWS LB Ingress Controller uses ALB/NLB)

Persistent Storage/Persistent Volumes - Volume whose lifecycle lives beyond any 1 pod using it.


  • Components in the Kubernetes system that monitor and manage the state of the resources running in a Kubernetes cluster.

Types of controllers

Replication Controller

  • Run multiple instances of a pod across the cluster providing fault tolerance and high availability
  • Even in a single node cluster, replication controller can be used to restart a pod if it fails


Replication controller is deprecated in favor of ReplicaSet


  • ReplicaSet is a controller that manages a set of pods
  • ReplicaSet ensures that a specified number of pod replicas are running at any given time
  • ReplicaSet is the next generation Replication Controller
  • ReplicaSet is the recommended way to manage pods