Java Spring Boot Microservices - Client Side Load Balancing with Spring Cloud LoadBalancer

Last Updated : 04 Jan, 2025

Spring Cloud is a collection of projects like load balancing, service discovery, circuit breakers, routing, micro-proxy, etc will be given by Spring Cloud. So spring Cloud basically provides some of the common tools and techniques and projects to quickly develop some common patterns of the microservices.

Basically, there are two ways to load balance the request

Client-Side Load Balancer
Server-Side Load Balancer

If you are keeping the load balancer on the client side and giving the load balancing responsibility to the client, then we called it Client-Side Load Balancing. And Spring Cloud LoadBalancer is one of the most popular client-side load balancers provided by Spring Cloud.

Note: Please refer to this article Spring Cloud - Load Balancer

What is Spring Cloud LoadBalancer and How to Use It?

The Spring Cloud Load Balancer library permits us to create applications that communicate with other applications in a load-balanced fashion. Using any algorithm we want, we can easily execute load balancing when making remote service calls.

How to Use Spring Cloud LoadBalancer?

Add the following dependency in your pom.xml file

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

Let's see the whole implementation by developing 2 Microservices and 1 Service Discovery. In brief, Client Side Load Balancing can happen with the help of LoadBalancerClient. You have to write the following logic in your client microservice inside the Service class.

@Autowired
private RestTemplate restTemplate;
@Autowired
private LoadBalancerClient loadBalancerClient;
// Get ServiceInstance list using serviceId
ServiceInstance serviceInstance = loadBalancerClient.choose("ADDRESS-SERVICE");
// Read URI and Add path that returns url
String uri = serviceInstance.getUri().toString();
// Get metadata
String contextPath = serviceInstance.getMetadata().get("configPath");
// Make HTTP call and get Response data
AddressResponse addressResponse = restTemplate.getForObject(uri + contextPath + "/address/{id}", AddressResponse.class, id);

Developing Service Discovery

Please refer to this article and develop a service discovery: Java Spring Boot Microservices - Developing Service Discovery.

Developing address-service Step by Step

Step 1: Create a New Spring Boot Project in Spring Initializr

To create a new Spring Boot project, please refer to How to Create a Spring Boot Project in Spring Initializr and Run it in IntelliJ IDEA. For this project choose the following things

Project: Maven
Language: Java
Packaging: Jar
Java: 17

Please choose the following dependencies while creating the project.

Spring Boot DevTools
Spring Data JPA
MySQL Driver
Spring Web
Eureka Discovery Client

Generate the project and run it in IntelliJ IDEA by referring to the above article.

Note: We have used the MySQL database in this project.

Step 2: Create Schema in MySQL Workbench and Put Some Sample Data

Go to your MySQL Workbench and create a schema named gfgmicroservicesdemo and inside that create a table called address and put some sample data as shown in the below image.

Address Table:

Here we have created 4 columns and put some sample data.

id
city
state
employee_id

Note: In the Address table, employee_id is a foreign key so create it accordingly. We are going to perform a SQL join operation in our native SQL query. So create tables carefully.

Spring-Boot-Native-Query-1

Before moving to IntelliJ IDEA let's have a look at the complete project structure for our Microservices.

Spring-Boot-Native-Query-2

Step 3: Make Changes in Your application.properties File

Now make the following changes in your application.properties file.

spring.datasource.url=jdbc:mysql://localhost:3306/gfgmicroservicesdemo
spring.datasource.username=put your username here
spring.datasource.password=put your password here
spring.application.name=address-service
server.port=8081
server.servlet.context-path=/address-service
eureka.instance.metadata-map.configPath=/address-service

Step 4: Create Your Entity/Model Class

Go to the src > main > java > entity and create a class Address and put the below code. This is our model class.

Java

package com.gfg.addressapp.entity;  import jakarta.persistence.*;  @Entity @Table(name = "address") public class Address {      @Id     @GeneratedValue(strategy = GenerationType.IDENTITY)     @Column(name = "id")     private int id;      @Column(name = "city")     private String city;      @Column(name = "state")     private String state;      public int getId() {         return id;     }      public void setId(int id) {         this.id = id;     }      public String getCity() {         return city;     }      public void setCity(String city) {         this.city = city;     }      public String getState() {         return state;     }      public void setState(String state) {         this.state = state;     } }

Step 5: Create Your Repository Interface

Go to the src > main > java > repository and create an interface AddressRepo and put the below code. This is our repository where we write code for all the database-related stuff.

Java

package com.gfg.addressapp.repository;  import com.gfg.addressapp.entity.Address; import java.util.Optional; import org.springframework.data.jpa.repository.JpaRepository; import org.springframework.data.jpa.repository.Query; import org.springframework.data.repository.query.Param;  @Repository public interface AddressRepo extends JpaRepository<Address, Integer> {      @Query(         nativeQuery = true,         value         = "SELECT ea.id, ea.city, ea.state FROM gfgmicroservicesdemo.address ea join gfgmicroservicesdemo.employee e on e.id = ea.employee_id where ea.employee_id=:employeeId")        Optional<Address> findAddressByEmployeeId(@Param("employeeId") int employeeId); }

Note: Please refer to this article to know more about JpaRepository.

Step 6: Create an AddressResponse Class

Go to the src > main > java > response and create a class AddressResponse and put the below code.

Java

package com.gfg.addressapp.response;  public class AddressResponse {      private int id;     private String city;     private String state;      public int getId() {         return id;     }      public void setId(int id) {         this.id = id;     }      public String getCity() {         return city;     }      public void setCity(String city) {         this.city = city;     }      public String getState() {         return state;     }      public void setState(String state) {         this.state = state;     } }

Step 7: Create Your Service Class

Go to the src > main > java > service and create a class AddressService and put the below code. This is our service class where we write our business logic.

Java

package com.gfg.addressapp.service;  import com.gfg.addressapp.entity.Address; import com.gfg.addressapp.repository.AddressRepo; import com.gfg.addressapp.response.AddressResponse; import org.modelmapper.ModelMapper; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service;  import java.util.Optional;  @Service public class AddressService {      @Autowired     private AddressRepo addressRepo;      @Autowired     private ModelMapper mapper;      public AddressResponse findAddressByEmployeeId(int employeeId) {         Optional<Address> addressByEmployeeId = addressRepo.findAddressByEmployeeId(employeeId);         AddressResponse addressResponse = mapper.map(addressByEmployeeId, AddressResponse.class);         return addressResponse;     }  }

Step 8: Create an Address Controller

Go to the src > main > java > controller and create a class AddressController and put the below code. Here we are going to create an endpoint "/address/{employeeId}" to find the address using employee_id. Thats why we have created a foreign key in the Address table and we have performed the SQL join operation in the native query to get our desired result.

Java

package com.gfg.addressapp.controller;  import com.gfg.addressapp.response.AddressResponse; import com.gfg.addressapp.service.AddressService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.http.HttpStatus; import org.springframework.http.ResponseEntity; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.PathVariable; import org.springframework.web.bind.annotation.RestController;  @RestController public class AddressController {      @Autowired     private AddressService addressService;      @GetMapping("/address/{employeeId}")     public ResponseEntity<AddressResponse> getAddressByEmployeeId(@PathVariable("employeeId") int employeeId) {         AddressResponse addressResponse = addressService.findAddressByEmployeeId(employeeId);         return ResponseEntity.status(HttpStatus.OK).body(addressResponse);     }  }

Step 9: Create a Configuration Class

Go to the src > main > java > configuration and create a class AddressConfig and put the below code.

Java

package com.gfg.addressapp.configuration;  import com.gfg.addressapp.service.AddressService; import org.modelmapper.ModelMapper; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration;  @Configuration public class AddressConfig {      @Bean     public ModelMapper modelMapperBean() {         return new ModelMapper();     }  }

Note: You may refer to these two articles
Spring @Configuration Annotation with Example
Spring @Bean Annotation with Example

Before running the Microservice below is the complete pom.xml file. Please cross-verify if you have missed some dependencies

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>3.0.2</version>         <relativePath/> <!-- lookup parent from repository -->     </parent>     <groupId>com.gfg.addressapp</groupId>     <artifactId>address-service</artifactId>     <version>0.0.1-SNAPSHOT</version>     <name>address-service</name>     <description>Address Service</description>     <properties>         <java.version>17</java.version>         <spring-cloud.version>2022.0.2</spring-cloud.version>     </properties>     <dependencies>         <dependency>             <groupId>org.springframework.boot</groupId>             <artifactId>spring-boot-starter-data-jpa</artifactId>         </dependency>         <dependency>             <groupId>org.springframework.boot</groupId>             <artifactId>spring-boot-starter-web</artifactId>         </dependency>          <dependency>             <groupId>org.springframework.boot</groupId>             <artifactId>spring-boot-devtools</artifactId>             <scope>runtime</scope>             <optional>true</optional>         </dependency>         <dependency>             <groupId>com.mysql</groupId>             <artifactId>mysql-connector-j</artifactId>             <scope>runtime</scope>         </dependency>         <dependency>             <groupId>org.springframework.boot</groupId>             <artifactId>spring-boot-starter-test</artifactId>             <scope>test</scope>         </dependency>         <dependency>             <groupId>org.modelmapper</groupId>             <artifactId>modelmapper</artifactId>             <version>3.1.1</version>         </dependency>          <dependency>             <groupId>org.springframework.cloud</groupId>             <artifactId>spring-cloud-starter-netflix-eureka-client</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>      <repositories>         <repository>             <id>netflix-candidates</id>             <name>Netflix Candidates</name>             <url>https://artifactory-oss.prod.netflix.net/artifactory/maven-oss-candidates</url>             <snapshots>                 <enabled>false</enabled>             </snapshots>         </repository>     </repositories>  </project>

Developing Employee-Service Step by Step

Step 1: Create a New Spring Boot Project in Spring Initializr

To create a new Spring Boot project, please refer to How to Create a Spring Boot Project in Spring Initializr and Run it in IntelliJ IDEA. For this project choose the following things

Project: Maven
Language: Java
Packaging: Jar
Java: 17

Please choose the following dependencies while creating the project.

Spring Boot DevTools
Spring Data JPA
MySQL Driver
Spring Web
Eureka Discovery Client

Generate the project and run it in IntelliJ IDEA by referring to the above article.

Note: We have used the MySQL database in this project.

Step 2: Create Schema in MySQL Workbench and Put Some Sample Data

Go to your MySQL Workbench and create a schema named gfgmicroservicesdemo and inside that create a table called employee and put some sample data as shown in the below image. Here we have created 4 columns and put some sample data.

id
name
email
age

Spring-Boot-Microservices-1-(2)

Now we are going to fetch Employee Data from Employee Table in our Spring Boot project. To do it refer to the following steps. Before moving to IntelliJ IDEA let's have a look at the complete project structure for our Microservices.

Spring-Boot-Microservices-3

Step 3: Make Changes in Your application.properties File

Now make the following changes in your application.properties file.

spring.datasource.url=jdbc:mysql://localhost:3306/gfgmicroservicesdemo
spring.datasource.username=put your username here
spring.datasource.password=put your password here
spring.application.name=employee-service
server.port=8080
# Set Your Context Path Here
server.servlet.context-path=/employee-service

You may also refer to the below image:

context-path-1

Step 4: Create Your Entity/Model Class

Go to the src > main > java > entity and create a class Employee and put the below code. This is our model class.

Java

package com.gfg.employeaap.entity;  import jakarta.persistence.*;  @Entity @Table(name = "employee") public class Employee {      @Id     @GeneratedValue(strategy = GenerationType.IDENTITY)     @Column(name = "id")     private int id;      @Column(name = "name")     private String name;      @Column(name = "email")     private String email;      @Column(name = "age")     private String age;      public int getId() {         return id;     }      public void setId(int id) {         this.id = id;     }      public String getName() {         return name;     }      public void setName(String name) {         this.name = name;     }      public String getEmail() {         return email;     }      public void setEmail(String email) {         this.email = email;     }      public String getAge() {         return age;     }      public void setAge(String age) {         this.age = age;     } }

Step 5: Create Your Repository Interface

Go to the src > main > java > repository and create an interface EmployeeRepo and put the below code. This is our repository where we write code for all the database-related stuff.

Java

package com.gfg.employeaap.repository;  import com.gfg.employeaap.entity.Employee; import org.springframework.data.jpa.repository.JpaRepository;  @Repository public interface EmployeeRepo extends JpaRepository<Employee, Integer> {  }

Note: Please refer to this article to know more about JpaRepository.

Step 6: Create an EmployeeResponse Class

Go to the src > main > java > response and create a class EmployeeResponse and put the below code.

Java

package com.gfg.employeaap.response;  public class EmployeeResponse {      private int id;     private String name;     private String email;     private String age;      public int getId() {         return id;     }      public void setId(int id) {         this.id = id;     }      public String getName() {         return name;     }      public void setName(String name) {         this.name = name;     }      public String getEmail() {         return email;     }      public void setEmail(String email) {         this.email = email;     }      public String getAge() {         return age;     }      public void setAge(String age) {         this.age = age;     } }

Step 7: Create Your Service Class

Go to the src > main > java > service and create a class EmployeeService and put the below code. This is our service class where we write our business logic.

Java

package com.gfg.employeaap.service;  import com.gfg.employeaap.entity.Employee; import com.gfg.employeaap.repository.EmployeeRepo; import com.gfg.employeaap.response.AddressResponse; import com.gfg.employeaap.response.EmployeeResponse; import org.modelmapper.ModelMapper; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.cloud.client.ServiceInstance; import org.springframework.cloud.client.loadbalancer.LoadBalancerClient; import org.springframework.stereotype.Service; import org.springframework.web.client.RestTemplate;  import java.util.Optional;  @Service public class EmployeeService {      @Autowired     private EmployeeRepo employeeRepo;      @Autowired     private ModelMapper mapper;      @Autowired     private RestTemplate restTemplate;      @Autowired     private LoadBalancerClient loadBalancerClient;      public EmployeeResponse getEmployeeById(int id) {          Optional<Employee> employee = employeeRepo.findById(id);         EmployeeResponse employeeResponse = mapper.map(employee, EmployeeResponse.class);          // Get ServiceInstance list using serviceId         ServiceInstance serviceInstance = loadBalancerClient.choose("ADDRESS-SERVICE");          // Read URI and Add path that returns url         String uri = serviceInstance.getUri().toString();          // Get metadata         String contextPath = serviceInstance.getMetadata().get("configPath");          // Make HTTP call and get Response data         AddressResponse addressResponse = restTemplate.getForObject(uri + contextPath + "/address/{id}", AddressResponse.class, id);          employeeResponse.setAddressResponse(addressResponse);         return employeeResponse;     }  }

Step 8: Create an Employee Controller

Go to the src > main > java > controller and create a class EmployeeController and put the below code. Here we are going to create an endpoint "/employees/{id}" to find an employee using id.

Java

package com.gfg.employeaap.controller;  import com.gfg.employeaap.response.EmployeeResponse; import com.gfg.employeaap.service.EmployeeService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.http.HttpStatus; import org.springframework.http.ResponseEntity; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.PathVariable; import org.springframework.web.bind.annotation.RestController;  @RestController public class EmployeeController {      @Autowired     private EmployeeService employeeService;      @GetMapping("/employees/{id}")     private ResponseEntity<EmployeeResponse> getEmployeeDetails(@PathVariable("id") int id) {         EmployeeResponse employee = employeeService.getEmployeeById(id);         return ResponseEntity.status(HttpStatus.OK).body(employee);     }  }

Step 9: Create a Configuration Class

Go to the src > main > java > configuration and create a class EmployeeConfig and put the below code.

Java

package com.gfg.employeaap.configuration;  import com.gfg.employeaap.service.EmployeeService; import org.modelmapper.ModelMapper; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration;  @Configuration public class EmployeeConfig {      @Bean     public ModelMapper modelMapperBean() {         return new ModelMapper();     }         @Bean     public RestTemplate restTemplate() {         return new RestTemplate();     }  }

Note: You may refer to these two articles
Spring @Configuration Annotation with Example
Spring @Bean Annotation with Example

Before running the Microservice below is the complete pom.xml file. Please cross-verify if you have missed some dependencies

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>3.0.2</version>         <relativePath/> <!-- lookup parent from repository -->     </parent>     <groupId>com.gfg.employeaap</groupId>     <artifactId>employee-service</artifactId>     <version>0.0.1-SNAPSHOT</version>     <name>employee-service</name>     <description>Employee Service</description>     <properties>         <java.version>17</java.version>         <spring-cloud.version>2022.0.2</spring-cloud.version>     </properties>     <dependencies>         <dependency>             <groupId>org.springframework.boot</groupId>             <artifactId>spring-boot-starter-data-jpa</artifactId>         </dependency>         <dependency>             <groupId>org.springframework.boot</groupId>             <artifactId>spring-boot-starter-web</artifactId>         </dependency>          <dependency>             <groupId>org.springframework.boot</groupId>             <artifactId>spring-boot-devtools</artifactId>             <scope>runtime</scope>             <optional>true</optional>         </dependency>         <dependency>             <groupId>com.mysql</groupId>             <artifactId>mysql-connector-j</artifactId>             <scope>runtime</scope>         </dependency>         <dependency>             <groupId>org.springframework.boot</groupId>             <artifactId>spring-boot-starter-test</artifactId>             <scope>test</scope>         </dependency>         <dependency>             <groupId>org.modelmapper</groupId>             <artifactId>modelmapper</artifactId>             <version>3.1.1</version>         </dependency>         <dependency>             <groupId>org.springframework.boot</groupId>             <artifactId>spring-boot-starter-webflux</artifactId>         </dependency>         <dependency>             <groupId>io.projectreactor</groupId>             <artifactId>reactor-test</artifactId>             <scope>test</scope>         </dependency>          <dependency>             <groupId>org.springframework.cloud</groupId>             <artifactId>spring-cloud-starter-netflix-eureka-client</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>      <repositories>         <repository>             <id>netflix-candidates</id>             <name>Netflix Candidates</name>             <url>https://artifactory-oss.prod.netflix.net/artifactory/maven-oss-candidates</url>             <snapshots>                 <enabled>false</enabled>             </snapshots>         </repository>     </repositories>  </project>

Run Your Services

Now run your both Address and Employee Microservices along with your Discovery Service. If everything goes well then you may see the following screen in your Eureka dashboard. Please refer to the below image.

Test Your Endpoint in Postman

Now open Postman and hit the following URL

GET: http://localhost:8080/employee-service/employees/2

And you can see the following response

{
    "id": 2,
    "name": "Asish",
    "email": "asis@gmail",
    "age": "30",
    "addressResponse": {
        "id": 1,
        "city": "BLS",
        "state": "Odisha"
    }
}

Please refer to the below image.

microservice-communication-3

Spring Cloud - Client Side Load Balancing with Ribbon

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Article Tags :

Practice Tags :

Java

Java Spring Boot Microservices - Client Side Load Balancing with Spring Cloud LoadBalancer

What is Spring Cloud LoadBalancer and How to Use It?

Developing Service Discovery

Developing address-service Step by Step

Developing Employee-Service Step by Step

Run Your Services

Test Your Endpoint in Postman

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