How to Use Config Server in Spring Cloud: Setup and Example

To use Spring Cloud Config Server, create a Spring Boot application with the @EnableConfigServer annotation and configure it to serve configuration files from a Git or local repository. Then, client applications connect to this server to fetch their configuration properties dynamically at startup or runtime.

Syntax

The basic setup involves creating a Spring Boot application annotated with @EnableConfigServer. You configure the server's source of configuration files in application.yml or application.properties. Clients use spring.cloud.config.uri to point to the config server URL.

• @EnableConfigServer: Activates the config server functionality.
• spring.cloud.config.server.git.uri: URL of the Git repo holding config files.
• spring.cloud.config.uri: Client property to locate the config server.

java/yaml

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.config.server.EnableConfigServer;

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

# application.yml for Config Server
spring:
  cloud:
    config:
      server:
        git:
          uri: https://github.com/your-repo/config-repo
          clone-on-start: true

# application.yml for Config Client
spring:
  application:
    name: demo-client
  cloud:
    config:
      uri: http://localhost:8888

Example

This example shows a simple Spring Cloud Config Server serving configuration from a GitHub repository and a client fetching properties from it.

The server runs on port 8888 and serves config files stored in the Git repo. The client application fetches its configuration from the server at startup.

java/yaml

/* Config Server Application (Java) */
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.config.server.EnableConfigServer;

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

/* application.yml for Config Server */
spring:
  cloud:
    config:
      server:
        git:
          uri: https://github.com/example/config-repo
          clone-on-start: true

server:
  port: 8888

/* Config Client Application (Java) */
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.beans.factory.annotation.Value;

@SpringBootApplication
@RestController
public class ConfigClientApplication {

    @Value("${custom.message:Default message}")
    private String message;

    public static void main(String[] args) {
        SpringApplication.run(ConfigClientApplication.class, args);
    }

    @GetMapping("/message")
    public String getMessage() {
        return message;
    }
}

/* application.yml for Config Client */
spring:
  application:
    name: demo-client
  cloud:
    config:
      uri: http://localhost:8888

server:
  port: 8080

Output

When you run the Config Server and then the Config Client, accessing http://localhost:8080/message returns the value of 'custom.message' from the Git repo config file, e.g., "Hello from Config Server!"

Common Pitfalls

• Incorrect Git URI: The config server won't start or serve configs if the Git repository URL is wrong or inaccessible.
• Missing @EnableConfigServer annotation: Without this, the app won't act as a config server.
• Client not pointing to server: Clients must set spring.cloud.config.uri to the server URL.
• Config file naming: Config files must follow the pattern {application}-{profile}.yml or {application}.yml in the repo.
• Network issues: Clients must be able to reach the config server URL.

yaml

/* Wrong client config (missing URI) */
spring:
  application:
    name: demo-client

/* Correct client config */
spring:
  application:
    name: demo-client
  cloud:
    config:
      uri: http://localhost:8888

Quick Reference

• Config Server: Annotate main class with @EnableConfigServer.
• Config Source: Set spring.cloud.config.server.git.uri to your config repo.
• Client Setup: Use spring.cloud.config.uri to point to the server.
• Config Files: Store files as {application}-{profile}.yml in the repo.
• Run Order: Start config server before clients.

Key Takeaways

Add @EnableConfigServer to your Spring Boot app to create a config server.

Configure the server to read config files from a Git repository or local source.

Clients must set spring.cloud.config.uri to fetch configuration from the server.

Ensure config files follow naming conventions like application-profile.yml in the repo.

Start the config server before client applications to avoid connection errors.