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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 architecture

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

  1. Creates a Pod

  2. Deploys nginx docker container inside the pod

Cluster

  • A cluster is a set of nodes grouped together

Controllers

  • 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

Warning

Replication controller is deprecated in favor of ReplicaSet

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