Introduction to Kubernetes (K8S)

Supported Container Runtimes

Pod is the smallest unit of kubernetes world. Just like in docker, we have smallest unit : container.
A pod contains multiple containers, shared volumes, shared IP address.
One container per pod is the most common use case.
A pod will be in one single server not distributed in multiple server.

A kubernetes cluster consists of one or more nodes. A node is basically a server.
Nodes can be kepts at different data centers, availablity zones but usually they are kept close to each other for better performance.
A node contains multiple pods. A pod contains multiple containers.
In kubernetes cluster, there are two types of nodes: master node and worker node. The master node manages all the worker nodes.
A master node is also called control plane.

There are some common services that runs on worker/master nodes. They are kubelet, kube-proxy, container-runtime (Docker / CRI-O/ Containerd).
In the master node, there is one service running named "API Server" that communicates with kubelet. This API Server is the main point of communication between multiple nodes.
Kube-proxy is responsible for network communication inside the node and between multiple nodes.
There are also some other services running in the master node.
- Scheduler : It manages and distributes loads accross multiple nodes.
- Kube Control Manager : It controls what happens in each node of the cluster.
- Cloud Control Manager : For running kubenetes in cloud (AWS, Azure, GCP).
- etcd : It stores logs of entire kubenetes cluster. Such logs are stored in key-value pais.
- DNS : For domain name resolution in the kubenetes cluster.

Cluster management is done by kubectl.
Kubectl is a command line tool that allows you to connect to remote kubernetes cluster and manage it locally.
It establishes HTTPS connection with API Server of master node so that we can manage the cluster.

minikube start --driver=docker

minikube ssh