Decomposing Monolithic to Microservices: Best practices
Decomposing a monolith into microservices — or designing microservices from scratch — requires careful planning to ensure scalability, maintainability, and team autonomy. Below are the best practices for decomposing microservices:
✅ 1. Decompose by Business Capability (Bounded Context)
- Use Domain-Driven Design (DDD) to identify bounded contexts.
- Each microservice should represent a single business function, e.g.:
-
UserService,OrderService,PaymentService
-
🎯 If your business team can “own” a domain, it's likely a good candidate for a microservice.
✅ 2. Don’t Share Databases
- Each microservice should own its data — no shared database.
- Enforce boundaries through separate schemas or databases.
- Use API or event-based communication to share data.
✅ 3. Keep Microservices Loosely Coupled, Strongly Cohesive
- Design services to operate independently.
- Group related functionality inside the service to avoid frequent cross-service calls.
✅ 4. Use API Gateways
- Centralize external access to internal services.
- Route, throttle, authenticate, and log API traffic.
Tools: Kong, Spring Cloud Gateway, NGINX
✅ 5. Use Asynchronous Communication Where Appropriate
- Use event-driven architecture (Kafka, RabbitMQ) for decoupling.
- Ideal for non-blocking operations like audit logging, notifications, analytics.
✅ 6. Decouple with Events or Queues
- Instead of calling service B from A synchronously, publish an event like
OrderPlaced. - Other services can subscribe and react.
✅ 7. Decide on Granularity Carefully
- Don’t make services too small too soon.
- Over-decomposition = complexity in communication, deployment, and testing.
Rule of thumb: If you're introducing more inter-service calls than internal logic — consider merging.
✅ 8. Autonomous Teams
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Align services with teams so they can build, deploy, and manage them independently.
“You build it, you run it” — Amazon Rule.
✅ 9. Handle Data Consistency
- Avoid distributed transactions (they are complex and error-prone).
- Use eventual consistency with patterns like:
- Saga
- Outbox Pattern
✅ 10. Centralize Cross-Cutting Concerns
| Concern | Solution |
|---|---|
| Logging | Use centralized logging (ELK, Loki) |
| Tracing | Use tools like Zipkin, Jaeger |
| Security | Use OAuth2/JWT with API Gateway |
| Config Management | Use Spring Cloud Config or Consul |
🧠 Bonus: Use the Strangler Fig Pattern for Migration
- Gradually replace parts of the monolith with microservices.
- Route new functionality to microservices, keep old in monolith.
✅ Summary Visual (Decomposition Checklist)
Aligned with business domain
Owns its data
Communicates via well-defined API
Deployable independently
Testable and observable
No tight coupling to other services