Services

A Service provides a stable network endpoint for a dynamic set of Pods whose IPs change over time.

Pods are temporary, Services are permanent.

Why Do We Need Services

Pods are created, destroyed, and rescheduled constantly.

Problem	Without Service	With Service
Pod restart	IP changes	Stable IP
Scaling	Manual routing	Built-in load balancing
Discovery	Hardcoded IP	DNS-based
Pod churn	Broken clients	Transparent

Services abstract network identity from Pod lifecycle.

Service Types

Type	Reachability	Typical Use
ClusterIP	Inside cluster	Internal backends
NodePort	NodeIP:Port	Simple external access
LoadBalancer	External IP	Cloud / LB integration
ExternalName	DNS alias	External dependencies

How Services Find Pods

Services use label selectors to discover Pods and create endpoints.

Endpoints update automatically as Pods scale or restart.

Service Discovery and DNS

Kubernetes runs CoreDNS.

DNS format:

<service>.<namespace>.svc.cluster.local

Clients connect using names, not IPs.

Hands-on Setup: Test Application

Create a Deployment

Input:

kubectl create deployment web --image=nginx

Output:

deployment.apps/web created

This creates Pods with label app=web.

Verify Pods

Input:

kubectl get pods -l app=web

Output:

web-xxxxx   1/1   Running

This confirms backend Pods are running.

ClusterIP Service

Create ClusterIP Service

Input:

kubectl expose deployment web --port=80 --name=web-clusterip

Output:

service/web-clusterip exposed

This exposes the service internally.

Inspect Service

Input:

kubectl get svc web-clusterip

Output:

NAME            TYPE        CLUSTER-IP     PORT(S)
web-clusterip   ClusterIP   10.96.12.45    80/TCP

This IP is reachable only inside the cluster.

NodePort Service

Create NodePort Service

Input:

kubectl expose deployment web --type=NodePort --port=80 --name=web-nodeport

Output:

service/web-nodeport exposed

This opens a port on every node.

Inspect NodePort

Input:

kubectl get svc web-nodeport

Output:

NAME            TYPE       PORT(S)
web-nodeport    NodePort   80:31234/TCP

This exposes the service at NodeIP:31234.

LoadBalancer Service

Create LoadBalancer Service

Input:

kubectl expose deployment web --type=LoadBalancer --port=80 --name=web-lb

Output:

service/web-lb exposed

This requests an external load balancer.

Inspect LoadBalancer

Input:

kubectl get svc web-lb

Output:

NAME     TYPE           EXTERNAL-IP
web-lb   LoadBalancer   <pending>

External IP assignment depends on the environment.

ExternalName Service

Create ExternalName Service

Input:

kubectl apply -f externalname.yaml

Output:

service/external-db created

This creates a DNS alias.

Example externalname.yaml:

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

Service Discovery Test

Create DNS Test Pod

Input:

kubectl run dns-test --image=busybox --restart=Never -- sleep 3600

Output:

pod/dns-test created

This Pod is used for connectivity tests.

Resolve Service Name

Input:

kubectl exec dns-test -- nslookup web-clusterip

Output:

Address: 10.96.12.45

This confirms Service DNS resolution.

Endpoints Verification

View Endpoints

Input:

kubectl get endpoints web-clusterip

Output:

10.244.0.5:80

This shows which Pods receive traffic.

Test Connectivity

Access Service Internally

Input:

kubectl exec dns-test -- wget -qO- web-clusterip

Output:

<!DOCTYPE html>
<html>
<title>Welcome to nginx!</title>

This confirms Service-to-Pod connectivity.

Key Takeaways

Concept	Meaning
Service	Stable access layer
ClusterIP	Internal networking
NodePort	Node-level exposure
LoadBalancer	External access
ExternalName	DNS alias
Endpoints	Pod backends

Services are the network glue that makes Kubernetes applications reliable and scalable.