What is Kubernetes

Kubernetes (K8s) is an open-source platform used to manage, scale, and run containerized applications automatically.

Kubernetes is a container orchestration tool that automates deployment, scaling, networking, and management of containers.

Kubernetes Architecture

Kubernetes Architecture. Ref : https://phoenixnap.com/kb/understanding-kubernetes-architecture-diagrams

When You Work Only With Docker

docker run myapp

What happens?

1. Docker pulls image

2. Creates container

3. Runs on one machine only

4. If it crashes → you restart manually

5. If you want 3 containers → you run command 3 times

6. No automatic load balancing

Kubernetes = Manages containers automatically across machines

In Docker you type:

docker run

In Kubernetes you type:

kubectl apply -f app.yaml

We need to start Kubernetes from Docker like below ,

API Server (Brain of Kubernetes)

Everything goes through API Server.

• Accepts your YAML file

• Stores configuration

• Tells cluster what to do

YAML file

etcd (The Memory)

In Docker:There is no central memory storing desired state.

In Kubernetes

etcd stores everything

Example:

1. You said: "I want 3 replicas"

2. That info is stored in etcd

   
   

Even if master restarts → configuration is safe.

Scheduler (Decision Maker)

Now question:Where should the container run?

If you have:

1. Worker Node 1

2. Worker Node 2

Scheduler decides which node has CPU/RAM available.

Controllers (Auto-Healing System)

Controllers constantly check:

Is actual state matching desired state?

Example:

1. You said 3 pods

2. One pod crashes

3. Controller sees only 2 running

4. Automatically creates 1 new pod

   
   

This is called:

Self Healing

Docker alone cannot do this automatically.

Worker Node

Worker node is where actual containers run.

Each worker node has:

Kubelet (Node Manager)

Think of Kubelet as:

The manager of that machine

It:

Talks to API server

1. Creates pods

2. Ensures containers are running

3. Reports health

Container Runtime (Docker)

Earlier Kubernetes used Docker directly.

Now it uses container runtimes like:

containerd

CRI-O

But concept same.

This actually runs the container.

Pod (Very Important)

In Docker:Container = smallest unit

In Kubernetes:Pod = smallest unit

Pod contains:

1. One or more containers

2. Shared network

3. Shared storage

Normally:1 Pod = 1 container

kube-proxy (Networking)

Handles:

1. Internal communication

2. Load balancing between pods

   
   

If 3 pods running:Traffic is automatically distributed.