Introduction

Collection of libraries (modules), each solving a specific problem, helps to build, run, and manage microservice systems.

Spring Boot  →  already built few services (different project)
Spring Cloud →  connect MANY services

• You already built multiple Spring Boot services
  • user-service
  • order-service
  • payment-service
• You want:
  • One entry point → API Gateway
  • Services to find each other → Eureka
  • Traffic spread across instances → Load Balancing
  • Shared configuration → Config Server

Architecture

                 Client
                    ↓
          ┌──────────────────┐
          │  API Gateway     │
          └──────────────────┘
                    ↓
     ┌──────────────┼──────────────┐
     │              │              │
User Service   Order Service   Payment Service
     │              │              │
     └─────── registers with Eureka ┘
                    ↑
             Service Registry
                    ↑
             Config Server (Git)
             
# External traffic → Gateway only
# Internal traffic → Service ↔ Service (Eureka)

Spring Cloud infrastructure services

Each are different Spring Boot projects:

1. config-server    (Spring Cloud Config)
2. service-registry (Eureka Server)
3. api-gateway      (Spring Cloud Gateway)

Config Server

1. Create another Spring Boot project, just for config files.

   Git Repo (configs)
    ├── user-service.yml
    ├── order-service.yml
    ├── payment-service.yml
    └── gateway.yml
   

2. Dependency: spring-cloud-starter-config

3. Main class enable config server

   @SpringBootApplication
   @EnableConfigServer
   public class ConfigServerApplication {
       public static void main(String[] args) {
           SpringApplication.run(ConfigServerApplication.class, args);
       }
   }