Kubernetes Core Concepts

🎯 Objective

By the end of this lesson, you will:

• Understand the essential components that make up a Kubernetes system
• Learn how these components work together
• Be able to identify the role of each core object in a typical Kubernetes setup

🧱 Kubernetes Cluster

A Kubernetes Cluster is a set of machines that work together to run containerized applications. It consists of:

• Master Node (Control Plane) – Manages the cluster
• Worker Nodes – Where the actual applications run

🖥️ Node

A Node is a single machine (VM or physical) in the cluster. Each node runs:

• kubelet: Talks to the control plane
• kube-proxy: Handles networking
• Container runtime (e.g., Docker or containerd)

There are two types:

• Master Node: Controls and manages the cluster
• Worker Node: Executes workloads (containers inside Pods)

📦 Pod

A Pod is the smallest deployable unit in Kubernetes. It can hold:

• One or more containers
• Shared storage
• Network resources

Note: If you deploy a single container, it’s still wrapped inside a Pod.

🔁 ReplicaSet

A ReplicaSet ensures a specified number of pod replicas are running at any given time. If a pod fails, it automatically creates a new one to replace it.

🚀 Deployment

A Deployment manages ReplicaSets and allows:

• Easy updates and rollbacks
• Scaling up/down
• Ensuring desired state is met

You define it in a YAML file, and Kubernetes does the rest.

🌐 Service

A Service provides a stable way to access your pods. Since pods have dynamic IPs, services allow consistent communication.

Types:

• ClusterIP – Internal communication
• NodePort – Accessible from outside on a static port
• LoadBalancer – Used in cloud environments for public access

🧭 Ingress

An Ingress is an API object that manages external access to services, typically HTTP/HTTPS. It acts as a smart router for incoming traffic.

📘 Example Scenario

Let’s say you want to run a website:

• You create a Deployment for your app (3 replicas)
• It runs inside Pods
• A ReplicaSet ensures all 3 are always running
• A Service exposes them
• An optional Ingress routes web traffic to the Service