Service Discovery in Microservices

Service discovery lets microservices find and communicate with each other dynamically, without hardcoded IPs.

The Problem

In dynamic environments, service instances:

• Scale up/down
• Restart with new IPs
• Move across hosts

Hardcoded endpoints break this dynamic nature.

Discovery Patterns

Client-Side Discovery

Client queries a service registry and chooses an instance.

Client → Registry → Get all instances of UserService
Client → Choose instance (load balance)
Client → Call UserService:8080

Tool: Netflix Eureka

Server-Side Discovery

Client calls load balancer which queries registry.

Client → Load Balancer → Registry lookup → Route

Tool: AWS ALB, Kubernetes

Service Registry

Tool	Type	Features
Consul	Distributed KV	Health checks, DNS
Eureka	Netflix OSS	Simple HTTP
Zookeeper	Coordination	Strong consistency
k8s DNS	Built-in	CoreDNS-based

Health Checks

Registry regularly polls services:

GET /health → 200 OK (healthy)
GET /health → 500 (removed from registry)

Self-Registration

Services register themselves on startup, deregister on shutdown.

Kubernetes DNS

In K8s, each Service gets a stable DNS name:

user-service.default.svc.cluster.local

Conclusion

Server-side discovery with Kubernetes DNS is the modern default. Use Consul for multi-cloud or VM-based environments.