Fault‑Tolerant Microservice Playground

Welcome to my hands‑on microservices lab a place where Spring Boot services roam free, Resilience4j keeps them safe, Eureka shows them the way home, and Docker + Kubernetes do the heavy lifting. This repo captures everything I’ve been tinkering with while learning to build, containerise, and harden cloud‑native apps.

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📚 What you’ll find

Layer	Tech	Why it’s here
Service	Spring Boot 3	Fast, opinionated Java foundation
Resilience	Resilience4j (Circuit Breaker, Retry, Rate Limiter, Bulkhead)	Protect each service from failure and overload
Discovery	Eureka Server + OpenFeign	Dynamic service lookup & type‑safe REST clients
Gateway	Spring Cloud Gateway	Single entry point, path routing, filters & rate limits
Config	Spring Cloud Config Server	Centralised, version‑controlled configuration
Docs	Springdoc‑OpenAPI (Swagger UI)	Live API documentation per service
Containers	Docker & Docker Compose	Repeatable local runs
Orchestration	Kubernetes manifests	Production‑ready deployment

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🏗️ Architecture at a glance

┌──────────────┐     ┌──────────────┐
│  React App   │──▶ │  Gateway      │──┐
└──────────────┘     └──────────────┘  │  (routes, rate‑limits)
                                        │
                                        ▼
     ┌───────────┬─────────────────────────────────────┐
     │ Eureka    │  Accounts │ Loans │ Cards │ …       │
     │ Registry  │<──────────┴─────────────────────────┘
     └───────────┘

Clients hit the Gateway, which discovers downstream services through Eureka. Each service carries Resilience4j guards that trip before trouble spreads.

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🚀 Quick start (Docker Compose)

# build all jars
./mvnw clean package -DskipTests

# spin everything up in detached mode
docker compose up -d --build

# tear everything down
docker compose down

Services become available at:

Service	URL
Gateway	http://localhost:8080
Eureka UI	http://localhost:8761
Config Server	http://localhost:8071/actuator/health
Swagger UI (Accounts)	http://localhost:9000/swagger-ui.html

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🔄 Resilience patterns implemented

Pattern	Where	Deep‑dive article
Circuit Breaker	@CircuitBreaker(name="accountsCB")	[Medium] Circuit Breaker in Spring Boot → https://medium.com/@araviku04/circuit-breaker-pattern-in-spring-boot-with-resilience4j-and-spring-cloud-gateway-5b4a0d2c161f
Rate Limiter	@RateLimiter(name="gatewayRL")	[Medium] Rate Limiter in Spring Cloud Gateway → https://medium.com/@araviku04/rate-limiter-pattern-in-microservices-using-spring-cloud-gateway-and-resilience4j-478373e68d44
Retry	@Retry(name="loansRetry")	[Medium] Retry Pattern → https://medium.com/@araviku04/retry-pattern-in-microservices-with-spring-boot-and-resilience4j-bbb9fbd47438
Bulkhead	@Bulkhead(name="cardsBH", type=THREADPOOL)	[Medium] Bulkhead Pattern → https://medium.com/@araviku04/bulkhead-pattern-in-microservices-with-spring-boot-resilience4j-7285e6e88a6f

Each pattern is wired with Spring Boot actuator metrics; hit /actuator/metrics/resilience4j.* to watch them in real time.

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🛰️ Service discovery & Feign clients

@FeignClient(name = "loans")
public interface LoansClient {
  @GetMapping("/loans/{customerId}")
  List<LoanDTO> fetchLoans(@PathVariable String customerId);
}

The name attribute matches the service‑ID registered in Eureka, giving us load‑balanced calls with zero hard‑coded URLs.

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⚙️ Centralised configuration

• Spring Cloud Config Server backed by a Git repo (config-repo/) holds properties per environment.
• Services bootstrap with spring.config.import=configserver: so new values can be hot‑reloaded via /actuator/refresh.

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📖 OpenAPI docs

Each service ships with springdoc‑openapi:

GET /v3/api-docs       # raw JSON
GET /swagger-ui.html   # interactive UI

Combine this with the Gateway’s aggregation to expose a single consolidated API portal.

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🐳 Docker cheat‑sheet

Need a quick reminder? Here are the commands I reach for most (IDs are trimmed for brevity):

#	Command	What it does
1	docker container logs -f <cid>	Tail container logs live
2	docker rm <cid>	Delete one or more stopped containers
3	docker container prune	Remove all stopped containers
4	docker image push <registry>/<user>:tag	Push image to registry
5	docker image pull <registry>/<user>:tag	Pull image from registry
6	docker image prune	Delete dangling/unused images
7	docker container stats	Live CPU/RAM/IO per container
8	docker system prune	Nuke stopped containers, networks, images & cache
9	docker rmi <img-id>	Remove one or more images
10	docker login -u <user>	Log in to Docker Hub
11	docker logout	Log out of Docker Hub
12	docker history <img>	Show image layer history
13	docker exec -it <cid> sh	Open interactive shell inside running container
14	docker compose up	Create & start services from compose file
15	docker compose down	Stop & remove services defined in compose