At FlowMart, we follow a set of design principles that guide the creation of new microservices. These principles help ensure our services are maintainable, scalable, and aligned with our overall architectural vision.

1. Domain-Driven Design

Each microservice should be aligned with a specific business domain or subdomain. We follow Domain-Driven Design (DDD) principles to identify service boundaries:

Bounded Contexts

• Define clear bounded contexts for each service
• Maintain a separate ubiquitous language within each context
• Document domain models and context maps

Example Domains at FlowMart

Domain	Description	Example Services
Order	Order processing and management	order-service, order-history-service
Inventory	Product inventory management	inventory-service, stock-management-service
Customer	Customer accounts and profiles	customer-service, authentication-service
Payment	Payment processing and refunds	payment-service, refund-service
Shipping	Shipping and logistics	shipping-service, tracking-service
Catalog	Product information management	product-service, search-service

2. Single Responsibility

Each microservice should have a single responsibility and a clear purpose:

• Focus on one business capability: Services should do one thing well
• Right-sized services: Not too large (mini-monolith) or too small (nano-service)
• Cohesive functionality: Related functions should be grouped together

3. Data Ownership

Microservices should own their data and maintain data autonomy:

• Each service has its own database or data store
• No direct data sharing between services
• Data is exposed through well-defined APIs
• Services should be the single source of truth for their domain data

4. API Design

All FlowMart microservices must follow our API Management and Governance Strategy:

RESTful APIs

• Use consistent resource naming conventions
• Follow standard HTTP methods and status codes
• Implement proper error handling and validation
• Design for backward compatibility

Event-Driven Interfaces

• Define clear event schemas using AsyncAPI
• Document event ownership and responsibilities
• Follow event versioning standards
• Implement idempotent event consumers

5. Resilience and Fault Tolerance

Microservices must be designed to handle failures gracefully:

• Implement circuit breakers for downstream dependencies
• Use timeouts and retries with exponential backoff
• Design for graceful degradation of functionality
• Implement health checks and readiness probes

6. Observability

All services must expose monitoring and observability data:

• Structured logging (using our ELK stack)
• Metrics exposure (Prometheus format)
• Distributed tracing support (Jaeger)
• Health check endpoints

7. Security by Design

Security must be integrated into every service:

• Authentication using OAuth 2.0 / OpenID Connect
• Authorization using role-based access control
• TLS encryption for all communications
• Input validation and output encoding
• No sensitive data in logs or traces

8. Testability

Services should be designed with testing in mind:

• High unit test coverage (minimum 80%)
• Integration tests for all critical paths
• Contract tests for API interfaces
• Easy local testing setup
• Simulated dependencies for development

9. Configuration Management

Services should follow our configuration management approach:

• Environment-specific configuration via Kubernetes ConfigMaps
• Secrets management via HashiCorp Vault
• Feature flags for conditional functionality
• No hardcoded configuration values

10. Independence and Deployability

Services should be independently deployable:

• No deployment coupling with other services
• Infrastructure as Code for all resources
• Self-contained CI/CD pipelines
• Blue/green or canary deployment capabilities

Microservice Checklist

Use this checklist when designing a new service:

• Service aligns with a specific business domain
• Clear bounded context defined
• Service owns its data
• APIs follow company standards
• Event schemas are documented
• Resilience patterns implemented
• Observability instrumentation added
• Security controls integrated
• Comprehensive test suite created
• Configuration externalized
• Independent deployment pipeline configured

Next Steps

• Learn how to create a Node.js microservice
• Explore TypeScript service implementation
• Understand our Terraform infrastructure modules