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name: spring-boot-microservices description: Standards for Feign clients and asynchronous messaging with Spring Cloud Stream. Use when implementing Feign HTTP clients or async event messaging in Spring Boot microservices. metadata: triggers: files: - '/*Client.java' - '/*Consumer.java' keywords: - feign-client - spring-cloud-stream - rabbitmq - resilience4j

Spring Boot Microservices Standards

Priority: P0 (CRITICAL)

Implementation Guidelines

Sync Communication (REST & API Interface)

• Clients: Use Spring Cloud OpenFeign or HTTP Interfaces (Spring 6/Java 21).
• Resilience: Implement Resilience4j with Circuit Breaker, Retry (Exponential Backoff), and RateLimiter.
• Contracts: Share DTO Records via Maven BOM or API Contract module.
• Tracing: Ensure Micrometer propagation for Distributed Tracing.

See implementation examples for Feign client with Circuit Breaker fallback.

Async Communication (Spring Cloud Stream)

• Architecture: Use Message-Driven patterns with Spring Cloud Stream.
• Functions: Define message handlers as java.util.function.Function, Consumer, or Supplier.
• Serialization: Use JSON or Avro for events.
• Reliability: Implement Dead Letter Queues (DLQ) and idempotent consumers.

See implementation examples for Spring Cloud Stream event consumer with idempotency.

Data & Isolation

• DB per Service: NEVER share databases between microservices.
• Shared Libs: Minimize shared logic to shared DTOs/Clients only.
• Discovery: Use Spring Cloud Gateway for routing and auth.

Anti-Patterns

• No Shared DB: Services must communicate via APIs or Events only.
• No Shared Entities: Share DTOs via Maven BOM, never JPA entities.
• No Sync Call Chains: Use async messaging to prevent distributed monolith.

References

• Implementation Examples