Spring Cloud Config (Server & Client)

To demonstrate the Spring Cloud Config concept we need 3 applications:

  1. Git Repository.
  2. Spring Cloud Config Server.
  3. Spring Cloud Config Client (the microservice application).

In the below diagram the interest-rates-service is a microservice where we had added the Spring Cloud Config Client dependency. Also there would be other microservices in the vicinity who may be using the same config server :

1. Git Repository:

We will name this application as – interest-rates-repo
(You can use local git repo as well, but in real life environment you will be using a remote git repo).

In the repo you can add below files:

interest-rates.properties
interest-rates-dev.properties
interest-rates-uat.properties

The above 3 files would be for production, development, and UAT respectively.

You can find the GitHub URL for the same here : https://github.com/heapsteep/interest-rates-repo.git

2. Spring Cloud Config Server:

Now we will create a spring boot project from Spring Initializr. We will give it this name- config-server . Add the below dependency and create the config server application:

One can see the below dependency in the pom.xml:

<dependency>
	<groupId>org.springframework.cloud</groupId>
	<artifactId>spring-cloud-config-server</artifactId>
</dependency>

Add below items in application.properties:

server.port=8888
spring.cloud.config.server.git.uri=https://github.com/heapsteep/interest-rates-repo.git
spring.cloud.config.server.git.default-label=master

The last line in the above properties file specifies the branch of the code you are considering. If you don’t specify that, you will get below exception:

org.springframework.cloud.config.server.environment.NoSuchLabelException: No such label: main
.
.
.
Caused by: org.eclipse.jgit.api.errors.RefNotFoundException: Ref main cannot be resolved

In the main class add below line:

@EnableConfigServer

Start the server. You can test the properties by calling below URL:

http://localhost:8888/interest-rates-dev.properties

http://localhost:8888/interest-rates.properties

If you change any of the value in the repo, the value in the config-server will be updated automatically, without any restart of the Config Server.

GitHub location for the above Config Server application is here: https://github.com/heapsteep/config-server.git

3. Spring Cloud Config Client:

Now lets create the Config Client, we will give it the name- interest-rates-service. In real life this would be the microservice application.
Create an spring boot application by importing below dependency:

One can see the below dependency in the pom.xml:

<dependency>
	<groupId>org.springframework.cloud</groupId>
	<artifactId>spring-cloud-starter-config</artifactId>
</dependency>

Create the bean class:

@Data
@AllArgsConstructor
public class InterestRates {
	int home;
	int motor;
}

And the controller:

@RestController
@RefreshScope
public class TestController {
	
	@Value("${interest.home}")
    private String home;
	
	@Value("${interest.motor}")
    private String motor;
		
	
	@GetMapping("/getRates") 
    @ResponseBody
    public InterestRates getRates() {
        return new InterestRates(Integer.parseInt(home),Integer.parseInt(motor));
    }
	
	@GetMapping("/getRate_home") 
    @ResponseBody
    public String getRate_home() {
        try {
            return this.home.toString();
        } catch (Exception e) {
            e.printStackTrace();
            return "Error: " + e.getMessage();
        }
    }

}

In application.properties: 

spring.application.name=interest-rates
server.port=8080
spring.config.import=optional:configserver:http://localhost:8888
spring.profiles.active=dev
management.endpoints.web.exposure.include=*

Just make sure that the value of spring.application.name should match with the the name of .properties file in the repo, i.e., interest-rates.properties file here.

In the above properties file we have set the profile to dev. If you want to make it to prod, just keep it blank.

http://localhost:8080/getRates

GitHub URL of the same Config Client can be found here: https://github.com/heapsteep/interest-rates-service.git

But still there is a problem- If you change some values in the repo, although it will automatically get updated in the config-server application, but it will not get updated automatically in the config-client application. You need to restart the config-client. To avoid the restart, you have to add below 3 changes in the code and do some other activities as mentioned below:

1.In the RestController class add this line: @RefreshScope.
2.Add the actuator dependency to config-client application.
3.Add the below line in bootstrap.properties. This will enable all actuator urls.

management.endpoints.web.exposure.include=*

Now from a REST client like Postman do a POST call (no body) to the below URL:
For Spring Boot 1.x+ call this URL: http://localhost:8080/refresh
For Spring Boot 2.0.0+ call this URL: http://localhost:8080/actuator/refresh

Finally, you will see the updated changes in config-client application.

But in real world, there would be lot of microservices. You can’t give a refresh call to each and every microservices running on different port. For that you have to take help of – Spring Cloud Bus.
But, with Spring Cloud Bus you can refresh all instances of a single microservice, but not for all microservice.