# Spring Boot Microservices

> 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. (triggers: **/*Client.java, **/*Consumer.java, feign-client, spring-cloud-stream, rabbitmq, resilience4j)

- Skill: `comeonoliver/spring-boot-microservices` (Agent Skill)
- Install (CLI): `npx skillmds@latest add comeonoliver/spring-boot-microservices`
- Raw SKILL.md: https://api.skillmd.com/api/skills/comeonoliver/spring-boot-microservices/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: DevOps & Infra
- Author: ComeOnOliver (https://skillmd.com/u/comeonoliver)
- Updated: 2026-09-08
- Page: https://skillmd.com/skills/comeonoliver/spring-boot-microservices

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# Spring Boot Microservices Standards

## **Priority: P0**

## 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`**. Use fallback methods to return cached or default data on failure. Configure timeout values on all Feign clients.
- **Contracts**: Share **`DTO Records`** via a **`Maven BOM`** or **`API Contract`** module.
- **Tracing**: Ensure **`Micrometers`** propagation for **Distributed Tracing**.

### 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.

### 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](references/implementation.md)