ETCD, Controller, API Server & Scheduler Deep Dive (In Practical Way)

 

Imagine you execute: kubectl run nginx --image=nginx

Flow:

Step 1

kubectl sends request.

kubectl --> API Server

Step 2

API Server validates request.

Create nginx Pod

Step 3

API Server stores desired state in ETCD.

ETCD --> nginx Pod Required

Step 4

Scheduler checks unscheduled pod.

Pod Needs Node

Finds best worker node.

Step 5

Scheduler updates ETCD.

Run Pod on Node-2

Step 6

Kubelet on Node-2 creates pod.

containerd pulls image

nginx starts

Step 7

Controller continuously checks:

Desired = 1 pod

Actual  = 1 pod

Healthy.