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