ADR-001: Microservices Architecture

Status

Accepted - July 2024

Context

BookWorm needs to demonstrate modern cloud-native patterns while maintaining educational value. The system must support:

• Independent development and deployment of different business capabilities
• Scalability for different service workloads
• Technology diversity for educational purposes
• Team autonomy in development practices
• Fault isolation and system resilience

The monolithic approach would be simpler but wouldn't demonstrate the complexities and benefits of distributed systems that are common in enterprise applications.

Decision

Adopt a microservices architecture with domain-driven service boundaries.

Service Boundaries

The system is decomposed into the following services based on business capabilities:

• Catalog Service: Book and author management
• Ordering Service: Purchase transactions and order management
• Basket Service: Shopping cart functionality
• Rating Service: Book reviews and ratings
• Chat Service: AI-powered book recommendations
• Notification Service: User communications
• Finance Service: Payment processing and financial transactions

Design Principles

• Domain-Driven Design: Services align with business domains
• Single Responsibility: Each service has one clear business purpose
• Data Ownership: Each service owns its data and database
• API-First: Well-defined service contracts
• Autonomous Teams: Services can be developed independently

Rationale

Why Microservices?

1. Educational Value: Demonstrates modern enterprise patterns
2. Scalability: Different services have different scaling requirements
3. Technology Diversity: Can showcase different .NET technologies
4. Team Simulation: Models real-world development scenarios
5. Cloud-Native Alignment: Works well with .NET Aspire and Azure

Service Decomposition Strategy

Services were identified using:

• Business capability mapping
• Data ownership boundaries
• Team organization considerations
• Scalability requirements
• Technology demonstration needs

Consequences

Positive Outcomes

• Independent Deployment: Services can be deployed separately
• Technology Diversity: Different services can use different technologies
• Team Autonomy: Teams can work independently on services
• Fault Isolation: Failure in one service doesn't crash the entire system
• Scalability: Services can be scaled independently based on demand
• Educational Value: Demonstrates real-world enterprise patterns

Negative Outcomes

• Operational Complexity: More services to monitor and manage
• Network Latency: Inter-service communication overhead
• Distributed System Challenges:
  • Data consistency across services
  • Distributed transaction management
  • Complex monitoring and debugging
• Testing Complexity: Integration testing becomes more complex
• Development Overhead: More infrastructure and deployment setup

Risk Mitigation

• Service Mesh: Consider implementing for complex routing and observability
• Circuit Breakers: Implement resilience patterns
• Distributed Tracing: Use OpenTelemetry for observability
• API Versioning: Implement versioning strategy early
• Documentation: Maintain clear service contracts and documentation

Alternatives Considered

Modular Monolith

• Pros: Simpler deployment, better performance, easier testing
• Cons: Less scalable, limited technology diversity, single point of failure
• Why Rejected: Doesn't demonstrate cloud-native patterns

Service-Oriented Architecture (SOA)

• Pros: Service reuse, enterprise integration patterns
• Cons: Too heavyweight, complex governance requirements
• Why Rejected: Overkill for the project scope and educational goals

Implementation Notes

• Services communicate via HTTP APIs and events
• Each service has its own database
• API Gateway provides unified entry point
• Service discovery handled by .NET Aspire
• Observability through OpenTelemetry

Related Decisions

• ADR-002: Event-Driven Architecture with CQRS
• ADR-003: .NET Aspire for Cloud-Native Development
• ADR-008: API Gateway Pattern Implementation