Config Server

🔍 What Is It?

Spring Cloud Config Server provides server-side and client-side support for externalized configuration.

Architecture:

• →Config Server — a Spring Boot app that serves config from a Git repo
• →Config Client — each microservice fetches its config from the server at startup
• →Git backend — stores config files (application.yml, order-service.yml, etc.)

Config file resolution:

For order-service with profile prod, the server serves (in priority order):

1. order-service-prod.yml
2. order-service.yml
3. application-prod.yml
4. application.yml

Dynamic refresh:

• →@RefreshScope on beans that should reload when config changes
• →POST /actuator/refresh triggers refresh on one instance
• →Spring Cloud Bus (Kafka/RabbitMQ) broadcasts refresh to all instances

🎯 Why Do We Need It?

In a microservices architecture with 20 services across dev/staging/prod, managing configuration is complex:

• →20 services × 3 environments = 60 config files to maintain
• →Changing a shared property requires updating all services
• →No audit trail for config changes

Config Server centralizes this: one Git repo, all services pull from it, Git history tracks all changes.

🏗️ What Happens in Real Projects?

Enterprise config management:

• →Database URLs per environment in Git
• →Feature flags managed centrally
• →Secrets via Spring Cloud Vault (not in Git)
• →Config changes without redeployment via @RefreshScope

⚙️ How It Works

Config Server clones the Git repo and serves config files via REST API. Clients call the server at startup (before the ApplicationContext is fully initialized) via bootstrap.yml or spring.config.import. The fetched properties are merged with local properties (local takes priority).

💻 Example

Config Server Setup — Server setup, client configuration, and dynamic refresh.

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

// application.yml for Config Server:
// server:
//   port: 8888
// spring:
//   cloud:
//     config:
//       server:
//         git:
//           uri: https://github.com/company/microservices-config
//           default-label: main
//           search-paths: '{application}'  # per-service subdirectory
//           username: ${GIT_USERNAME}
//           password: ${GIT_TOKEN}

🤔 Common Confusions

🚨 Common Production Issues

✅ Best Practices

🏛️ Architect's Note

💬 Frequently Asked Questions

🎯 Key Takeaways

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