Service Discovery

What is Service Discovery?

Service Discovery is the mechanism by which services locate each other in a distributed system. In dynamic environments where services scale up/down and IP addresses change, hardcoding addresses is impractical.

The Problem

What if Service B scales or moves?

Service Discovery Types

Client-Side Discovery

Client queries registry and chooses which instance to call:

Examples: Netflix Eureka, Consul (client mode)

Server-Side Discovery

Load balancer queries registry and routes request:

Examples: AWS ALB, Kubernetes Services

Service Registry

Central database of service instances:

Registration Patterns

Self-Registration

Service registers itself on startup:

Third-Party Registration

Separate registrar watches and registers services:

Health Checking

Ensure only healthy instances receive traffic:

Popular Solutions

Kubernetes Service Discovery

# Service definition
apiVersion: v1
kind: Service
metadata:
  name: user-service
spec:
  selector:
    app: user
  ports:
    - port: 80
      targetPort: 8080

Access via DNS: user-service.namespace.svc.cluster.local

Interview Tips

• Explain client-side vs server-side discovery
• Describe service registry and health checks
• Know tools: Consul, etcd, Kubernetes DNS
• Discuss registration patterns (self vs third-party)
• Mention challenges: consistency, availability of registry