🧩 Kubernetes Services - End-to-End Guide

In Kubernetes, Pods are short-lived and dynamic. When they restart or scale, their IPs change. To maintain consistent communication across services and ensure accessibility, Kubernetes Services act as a stable endpoint and load balancer.

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🚀 What is a Kubernetes Service?

A Kubernetes Service is an abstraction layer that defines a logical set of Pods and a policy by which to access them. Services provide:

• A stable DNS name
• A stable IP address
• Optional load balancing for traffic

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🔍 Why Services Are Needed

• Pods are ephemeral and can die or be recreated with new IPs
• Services allow apps to reliably communicate
• Services offer load balancing across multiple Pods
• You can expose apps inside or outside the cluster

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🧱 Types of Kubernetes Services

Type	Description	Scope	Example Use Case
ClusterIP	Default; exposes the Service on internal IP	Internal Only	Backend to Database communication
NodePort	Exposes Service on a static port on nodes	External Access	Quick dev/test exposure
LoadBalancer	Provisions external cloud load balancer	Public Access	Production frontend API/UI
ExternalName	Maps Service to external DNS	External Redirect	Use RDS or external API from a Pod

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🏗️ Real-World Architecture

Example: A full-stack app

• 🔹 Frontend (React App) – needs to be accessed by users over the internet
  → LoadBalancer
• 🔹 Backend (Node.js/Java Spring) – accessed only by frontend
  → ClusterIP
• 🔹 Database (PostgreSQL/MongoDB) – accessed only by backend
  → No Service or Headless Service (StatefulSet)

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📦 Service YAML Examples

1️⃣ ClusterIP Service (Default)

apiVersion: v1
kind: Service
metadata:
  name: backend-service
spec:
  selector:
    app: backend
  ports:
    - protocol: TCP
      port: 80         # Service port (inside cluster)
      targetPort: 5000 # Container port
  type: ClusterIP

Explanation:

• Selects Pods with label app=backend
• Routes traffic from port 80 to container port 5000
• Only accessible within the cluster

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2️⃣ NodePort Service

apiVersion: v1
kind: Service
metadata:
  name: frontend-service
spec:
  selector:
    app: frontend
  ports:
    - port: 80
      targetPort: 3000
      nodePort: 30080
  type: NodePort

Explanation:

• Exposes app externally via NodeIP:30080
• Great for dev or testing
• nodePort must be between 30000-32767

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3️⃣ LoadBalancer Service (Cloud Only)

apiVersion: v1
kind: Service
metadata:
  name: frontend-loadbalancer
spec:
  selector:
    app: frontend
  ports:
    - protocol: TCP
      port: 80
      targetPort: 3000
  type: LoadBalancer

Explanation:

• Creates a cloud load balancer (AWS/GCP/Azure)
• Auto-assigns a public IP
• Ideal for production/public APIs

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4️⃣ ExternalName Service

apiVersion: v1
kind: Service
metadata:
  name: external-db
spec:
  type: ExternalName
  externalName: database.example.com

Explanation:

• No selector or endpoint created
• Requests to this service DNS redirect to external FQDN

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⚙️ How Services Work Internally

1. kube-proxy runs on each node.
2. It watches for Services and Endpoints.
3. It sets up:
   • iptables or IPVS rules for routing
   • DNS via kube-dns or CoreDNS for name resolution
4. Load balances traffic to matching Pods

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🛰️ Accessing Services

Method	Usage
kubectl port-forward	Local testing
NodePort	Access via IP of any cluster node
LoadBalancer	Get public IP from your cloud provider
Ingress (with controller)	Advanced routing with domains and paths

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📖 Useful Commands

# Create a service from a YAML file
kubectl apply -f service.yaml

# List all services
kubectl get svc

# Get detailed info
kubectl describe svc <service-name>

# Delete a service
kubectl delete svc <service-name>

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✅ Best Practices

• Use ClusterIP for internal microservices communication
• Use NodePort only for local or quick access
• Use LoadBalancer in production environments
• For external APIs (e.g., AWS RDS, Stripe), use ExternalName
• For traffic routing and SSL, consider Ingress + TLS certs

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🧪 Testing Locally

# Port forward backend to localhost
kubectl port-forward svc/backend-service 8080:80

# Now you can access it on http://localhost:8080

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🧩 Summary

Type	Internal	External	Cloud Integration	Use For
ClusterIP	✅	❌	❌	Microservice to microservice
NodePort	✅	✅	❌	Quick dev testing
LoadBalancer	✅	✅	✅	Public APIs, websites
ExternalName	❌	✅	✅ (DNS only)	RDS, external APIs

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