Create a Load Balancer Using Java

Load balancing server [netflix-eureka-naming-server], Server application [micro-service-server], and Client application [micro-service-client].

Vishnu Viswambharan

Updated Jun. 11, 20 · Tutorial

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This Architecture Contains Three Applications

Load balancing server [netflix-eureka-naming-server]
Server application [micro-service-server]
Client application [micro-service-client]

Network Architecture of the System

Eureka naming server

Steps to Run Applications

Install JDK 11 or the latest.
Clone git repository of the project into local.
Github: https://github.com/VishnuViswam/LOAD-BALANCER
Run Netflix-eureka-naming-server application first.
Then run a microservice-server application in two ports.
At last run micro-service-client.

Working and Configurations

1) Load Balancing Server

All client-server communication will be done through this load balancing server.

pom.xml

We are using Netflix-eureka-server library to enable the communication between client and server.

    XML
   
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<properties>
    <java.version>11</java.version>  
    <spring-cloud.version>Hoxton.SR4</spring-cloud.version>
</properties> 
<dependencies>
  <dependency>    
    <groupId>org.springframework.cloud</groupId>    
    <artifactId>spring-cloud-starter-config</artifactId>
  </dependency>  
  <dependency>
    <groupId>org.springframework.cloud</groupId>    
    <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>  </dependency> 
</dependencies>

application.properties

    Properties files
   
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# application unique name
spring.application.name=netflix-eureka-naming-server
# it will be the default port which eureka naming server 
server.port=8761
eureka.client.register-with-eureka=false
eureka.client.fetch-registry=false

NetflixEurekaNamingServerApplication.java

@EnableEurekaServer annotation will allow the eureka server to control this application.

    Java
   
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@SpringBootApplication
@EnableEurekaServer // to enable the communication with Eureka server 
public class NetflixEurekaNamingServerApplication { 
    public static void main(String[] args) {         SpringApplication.run(NetflixEurekaNamingServerApplication.class, args);     
                                           } 
}

After running this application we can access the Eureka server dashboard in the following URL

URL: http://localhost:8761

Eureka Server Dashboard

spring eureka

2) Server Application

To perform load distribution, this application needs to run in two instances.
spring-cloud-starter-Netflix-eureka-client used to enable communication with Eureka naming server

    XML
   
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<dependency>
  <groupId>org.springframework.cloud</groupId>  
  <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
</dependency>

pom. xml

    XML
   
xxxxxxxxxx

<properties>  
  <java.version>11</java.version>  
  <spring-cloud.version>Hoxton.SR4</spring-cloud.version> 
</properties> 
<dependencies>  
  <dependency>    
    <groupId>org.springframework.cloud</groupId>    
    <artifactId>spring-cloud-starter-config</artifactId> 
  </dependency> 
  <dependency>  
    <groupId>org.springframework.cloud</groupId>  
    <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>     </dependency>
</dependencies>

application. properties

    Properties files
   
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# application unique name 
spring.application.name=micro-service-server
# application will be running under this port 
server.port=4000
# end point of load balancing server 
eureka.client.service-url.default-zone=http://localhost:8761/eureka

MicroServiceServerApplication.java

@EnableDiscoveryClient annotation to register the application with the eureka server.

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

ServerController.java

It is an ordinary rest controller class

    Java
   
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@RestController
@RequestMapping("/server")
public class ServerController {
    @Autowired
    private Environment environment;
    @GetMapping("/technologyInfo/{platform}")
    public ResponseModel retrieveTechnologyInfo(@PathVariable("platform") String platform) {
        ResponseModel responseModel = new ResponseModel();
        if (platform.equalsIgnoreCase("Java")) {
            responseModel.setTittle("Technology Stack");
            responseModel.setPlatform("Java");
            responseModel.setUsedFor("Secured Web Services");
        } else if (platform.equalsIgnoreCase("python")) {
            responseModel.setTittle("Technology Stack");
            responseModel.setPlatform("python");
            responseModel.setUsedFor("Machine Learning");
        } else {
            responseModel.setTittle("Technology Stack");
            responseModel.setPlatform(platform);
            responseModel.setUsedFor("Unknown platform");
        }
        responseModel.setServerPort(Short.parseShort(environment.getProperty("local.server.port")));
        return responseModel;
    }
    ;
}

ResponseModel.java

It is a traditional model class.

    Java
   
xxxxxxxxxx

public class ResponseModel {
  private String tittle;
  private String platform;
  private String usedFor;
  private Short serverPort;
  /** constructor with getters and setters **/
}

Run Server Application Instance in Two Ports

First, simply run the application as a java application using the main method. To run one more instance in another port we need to edit the Run/Debug Configurations In the IDE.

In IntelliJ

Click on the Edit Configuration option, it will be available on the right top side of the menu bar.

edit configurations

It will open a window as follows. Then enable Allow parallel run and press apply.

TestWorkSpace

Now change the port in the property file as 4001. Then run once again.

In Eclipse

Right-click on the main class -> click properties -> select main class -> click new button and add -Server. port=4001 in the VM Arguments as shown in the following images.

run/debug

testapplication

Then select the new configuration and run. Now, these two instances of the server will appear in the eureka server dashboard.

3) Client Application

This application will perform as a consumer of APIs which is written in the main server.
It consumes the APIs from both main server instances based on availability through the load balancer.
We also use the Netflix-eureka-client library to communicate with the load balancer application.

OpenFeign

We are using OpenFeign to consume APIs rather than using traditional HTTP libraries.
OpenFeign will act as a proxy in between server and client.

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

Eureka Client and Ribbon

Ribbon will do the automatic switching of servers in the client-side
Eureka will help us to dynamically add main server instances to the load balancer according to traffic.

    XML
   
xxxxxxxxxx

<dependency>  
  <groupId>org.springframework.cloud</groupId>  
  <artifactId>spring-cloud-starter-netflix-ribbon</artifactId>
</dependency>
<dependency> 
  <groupId>org.springframework.cloud</groupId> 
  <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
</dependency>

pom.xml

    XML
   
xxxxxxxxxx

<properties> 
  <java.version>11</java.version> 
  <spring-cloud.version>Hoxton.SR4</spring-cloud.version>
</properties> 
<dependencies> 
  <dependency>  
    <groupId>org.springframework.cloud</groupId>   
    <artifactId>spring-cloud-starter-config</artifactId> 
  </dependency> 
  <dependency> 
    <groupId>org.springframework.cloud</groupId> 
    <artifactId>spring-cloud-starter-openfeign</artifactId> 
  </dependency> 
  <dependency>  
    <groupId>org.springframework.cloud</groupId>  
    <artifactId>spring-cloud-starter-netflix-ribbon</artifactId> 
  </dependency> 
  <dependency>   
    <groupId>org.springframework.cloud</groupId>  
    <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>  </dependency>
</dependencies>

application.properties

    Properties files
   
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# application unique name 
server.servlet.contextPath=/microservice
# application will be running under this port 
spring.application.name=micro-service-client server.port=5000
# end point of load balancing server 
eureka.client.service-url.default-zone=http://localhost:8761/eureka

MicroServiceClientApplication.java

@EnableDiscoveryClient annotation used to register the application with the eureka server in the main class.
@EnableFeignClients annotation used to connect the feign library.

    Java
   
xxxxxxxxxx

@SpringBootApplication
@EnableFeignClients("com.microservices.client") 
@EnableDiscoveryClient
public class MicroServiceClientApplication {  
  public static void main(String[] args) { 
    SpringApplication.run(MicroServiceClientApplication.class, args);  
                                         } 
}

ClientController.java

It is an ordinary rest controller class

    Java
   
xxxxxxxxxx

@RestController
@RequestMapping("/client")
public class ClientController {
  @Autowired
  private ApiProxy apiProxy;
  @GetMapping("/technologyInfo/{platform}")
  public ResponseModel getTechnologyInfo(@PathVariable("platform") String platform) {
    /**API calling using proxy interface and mapping into ResponseModel named Object.**/
    ResponseModel responseModel = apiProxy.retrieveTechnologyInfo(platform);
    return responseModel;
                                                                                    }
}

ApiProxy.java

Act as a proxy class in between API and client.
@FeignClient(name = "micro-service-server") annotation will configure the information of the API exposed application name.
@RibbonClient(name = "micro-service-server") annotation will feed the client application with a load-balanced server name.

    Java
   
xxxxxxxxxx

@FeignClient(name = "micro-service-server")
@RibbonClient(name = "micro-service-server")
public interface ApiProxy {
  @GetMapping("/server/technologyInfo/{platform}")
  ResponseModel retrieveTechnologyInfo(@PathVariable("platform") String platform);
}

ResponseModel.java

It is a traditional model class.

    Java
   
          x
         
public class ResponseModel {
  private String tittle;
  private String platform;
  private String usedFor;
  private Short serverPort;
  /** constructor with getters and setters **/
}

After running client application, an instance of this application also appear in the eureka server dashboard.
Finally, Eureka Server Dashboard will be as follows.

DS Replicas

Result

All client application API to see the load balancing magic.

URI: http://localhost:5000/microservice/client/technologyInfo/java

Response:

    Java
   
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{"tittle":"Technology Stack","platform":"Java","usedFor":"Secured Web Services","serverPort":4000}

To refresh:

    Java
   
xxxxxxxxxx

{"tittle":"Technology Stack","platform":"Java","usedFor":"Secured Web Services","serverPort":4001}

From the result, we can understand that the API response is receiving from different servers by identifying port change.

Load balancing (computing) Java (programming language) application

Published at DZone with permission of Vishnu Viswambharan. See the original article here.

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Create a Load Balancer Using Java

Load balancing server [netflix-eureka-naming-server], Server application [micro-service-server], and Client application [micro-service-client].

This Architecture Contains Three Applications

Network Architecture of the System

Steps to Run Applications

Working and Configurations

1) Load Balancing Server

pom.xml

application.properties

NetflixEurekaNamingServerApplication.java

Eureka Server Dashboard

2) Server Application

pom. xml

application. properties

MicroServiceServerApplication.java

ServerController.java

ResponseModel.java

Run Server Application Instance in Two Ports

In IntelliJ

In Eclipse

3) Client Application

OpenFeign

Eureka Client and Ribbon

pom.xml

application.properties

MicroServiceClientApplication.java

ClientController.java

ApiProxy.java

ResponseModel.java

Result

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