Tuesday, March 30, 2021

Create Spring Boot Application With Centralized Configuration

Create Spring Boot Application With Centralized Configuration

We will see how to create a spring boot application with centralized configuration.

Pre-requisites for below tutorial:

  • JDK 1.8 or later
  • Maven
  • Git

This requires two applications:

  1. a configuration service application (config-server)
  2. a configuration client application (config-client)
1. Create a configuration service application - Config Server

For the service application, visit the Spring Initializr to generate a new project with the required dependency (Config Server).

pom.xml 

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.4.4</version>
		<relativePath /> <!-- lookup parent from repository -->
	</parent>
	<groupId>info.code2learn</groupId>
	<artifactId>config-server</artifactId>
	<name>config-server</name>
	<description>Configuration Server</description>

	<properties>
		<java.version>8</java.version>
		<spring-cloud.version>2020.0.2</spring-cloud.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-configuration-processor</artifactId>
			<optional>true</optional>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-config-server</artifactId>
		</dependency>
	</dependencies>
	<dependencyManagement>
		<dependencies>
			<dependency>
				<groupId>org.springframework.cloud</groupId>
				<artifactId>spring-cloud-dependencies</artifactId>
				<version>${spring-cloud.version}</version>
				<type>pom</type>
				<scope>import</scope>
			</dependency>
		</dependencies>
	</dependencyManagement>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

You first need a Config Server to act as a sort of intermediary between your Spring applications and a version-controlled repository of configuration files. You can use Spring Cloud’s @EnableConfigServer to standup a config server that can communicate with other applications. This is a regular Spring Boot application with one annotation added to enable the config server. 
ConfigServerApplication.java
  
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.config.server.EnableConfigServer;

@EnableConfigServer
@SpringBootApplication
public class ConfigServerApplication {

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

}



The Config Server needs to know which repository to manage. There are several choices here, but start with a Git-based file system repository. You could as easily point the Config Server to a Github or GitLab repository.

On the file system, create a new directory and run git init in it. Then add below files in the directory. 

  • config-client.properties
  • config-client-staging.properties
  • config-client-production.properties
Then run git commit in it.

Later, you will connect to the Config Server with a Spring Boot application whose spring.application.name property identifies it as config-client to the Config Server. This is how the Config Server knows which set of configuration to send to a specific client. It also sends all the values from any file named application.properties or application.yml in the Git repository. Property keys in more specifically named files (such as config-client.properties) override those in application.properties or application.yml.

Add a simple property and value with different message related to specific environment (eg.welcome.message = Welcome to config client) to the newly created config-client-<label>.properties files and then  commit the changes using git commit .

config-client.properties 

    server.port=8080
config-client-staging.properties 

    welcome.message=Welcome To Config Client Application - staging
config-client-production.properties 

    welcome.message=Welcome To Config Client Application - production

Specify the path to the Git repository by specifying the spring.cloud.config.server.git.uri property in configuration-service/src/main/resources/application.properties. You must also specify a different server.port value to avoid port conflicts when you run both this server and another Spring Boot application on the same machine. The following listing (from configuration-service/src/main/resources/application.properties) shows such an application.properties file: 


server.port=8888
spring.cloud.config.server.git.uri=${HOME}/Desktop/config-files
2. Create a configuration client application - Config Client
Now we need to create a client application which loads property files from config server. We need to add the org.springframework.cloud:spring-cloud-starter-config  dependency, to connect to the Config Server. 

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.4.4</version>
		<relativePath /> <!-- lookup parent from repository -->
	</parent>
	<groupId>info.code2learn</groupId>
	<artifactId>config-client</artifactId>
	<name>config-client</name>
	<description>Configuration Client</description>
	
	<properties>
		<java.version>8</java.version>
		<spring-cloud.version>2020.0.2</spring-cloud.version>
	</properties>
	
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-actuator</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-config</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
	</dependencies>

	<dependencyManagement>
		<dependencies>
			<dependency>
				<groupId>org.springframework.cloud</groupId>
				<artifactId>spring-cloud-dependencies</artifactId>
				<version>${spring-cloud.version}</version>
				<type>pom</type>
				<scope>import</scope>
			</dependency>
		</dependencies>
	</dependencyManagement>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>
Specify the client’s  spring.application.nameas  config-clientand the location of the Config Server spring.config.importin config-client/src/main/resources/application.properties. 
config-client/src/main/resources/application.properties
spring.application.name=config-client
spring.config.import=optional:configserver:http://localhost:8888/
management.endpoints.web.exposure.include=*

The client can access any value in the Config Server by using the traditional mechanisms (such as @ConfigurationProperties or @Value("${…​}") or through the Environment abstraction).

Create a rest controller that returns the resolved message property’s value. 

ConfigClientApplication.java

package info.code2learn.configclient;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.context.config.annotation.RefreshScope;

@RefreshScope
@SpringBootApplication
public class ConfigClientApplication {

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

}


ConfigClientController.java

package info.code2learn.configclient.controller;

import org.springframework.beans.factory.annotatioTest the Applicationn.Value;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class ConfigClientController {
	
	@Value("${welcome.message}")
	private String message;
	
	@RequestMapping("/message")
	public ResponseEntity<String> message(String name) {
		return new ResponseEntity<String>(message, HttpStatus.OK);
	}
	
}

Test the application

Start the Config Server first and then, once it is running, start the client using profile 'staging' or 'production' (eg. mvn spring-boot:run -Dspring-boot.run.profiles=staging). Open the client app in the browser using url http://localhost:8080/message . There, you should see Welcome message in the response specific to the profile.






You can also see the configuration details for a particular client application using  http://localhost:8888/config-client/staging


Click here for github link
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