Microservices with Spring Boot - Part 4 - Load Balancing Example - Using Ribbon


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Let’s learn the basics of microservices and microservices architectures. We will also start looking at a basic implementation of a microservice with Spring Boot. We will create a couple of microservices and get them to talk to each other using Eureka Naming Server and Ribbon for Client Side Load Balancing.

Here is the Microservice Series Outline: Microservices with Spring Boot

This is part 4 of this series. In this part, we will focus on using Ribbon for Load Balancing.

You will learn

  • What is the need for Load Balancing?
  • What is Ribbon?
  • How do you add Ribbon to your Spring Boot Project?
  • How do you enable and configure Ribbon to do Load Balancing?

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Microservices Overview

In the previous two parts, we created the microservices and established communication between them.

GET to http://localhost:8100/currency-converter-feign/from/EUR/to/INR/quantity/10000

{
  id: 10002,
  from: "EUR",
  to: "INR",
  conversionMultiple: 75,
  quantity: 10000,
  totalCalculatedAmount: 750000,
  port: 8000,
}

When we execute the above service, you would see that a request is also sent over to the forex-service.

Thats cool!

We have now created two microservices and established communication between them.

Image

However, we are hardcoding the url for FS in CCS component CurrencyExchangeServiceProxy.

@FeignClient(name="forex-service" url="localhost:8000")
public interface CurrencyExchangeServiceProxy {
  @GetMapping("/currency-exchange/from/{from}/to/{to}")
  public CurrencyConversionBean retrieveExchangeValue
    (@PathVariable("from") String from, @PathVariable("to") String to);
}

That means when new instances of Forex Service are launched up, we have no way to distributing load to them.

In this part, let’s now enable client side load distribution using Ribbon.

Tools you will need

  • Maven 3.0+ is your build tool
  • Your favorite IDE. We use Eclipse.
  • JDK 1.8+

Complete Maven Project With Code Examples

Our Github repository has all the code examples - https://github.com/in28minutes/spring-boot-examples/tree/master/spring-boot-basic-microservice

Enabling Ribbon

Add Ribbon Dependency to pom.xml

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

Enable RibbonClient in CurrencyExchangeServiceProxy

@FeignClient(name="forex-service")
@RibbonClient(name="forex-service")
public interface CurrencyExchangeServiceProxy {

Configure the instances in application.properties

forex-service.ribbon.listOfServers=localhost:8000,localhost:8001

Launch up Forex Service on 8001

In the above step, we configured ribbon to distribute load to instances. However, we do not have any instance of Forex Service running on 8001.

We can launch it up by configuring a launch configuration as shown in the figure below.

Image

Ribbon in Action

Currently we have the following service up and running

  • Currency Conversion Micro Service (CCS) on 8100
  • Two instances of Forex MicroService on 8000 and 8001

Now you would see that the requests to CCS would get distributed between the two instances of Forex Microservice by Ribbon

Request 1

GET to http://localhost:8100/currency-converter-feign/from/EUR/to/INR/quantity/10000

{
  id: 10002,
  from: "EUR",
  to: "INR",
  conversionMultiple: 75,
  quantity: 10000,
  totalCalculatedAmount: 750000,
  port: 8000,
}

Request 2

GET to http://localhost:8100/currency-converter-feign/from/EUR/to/INR/quantity/10000

{
  id: 10002,
  from: "EUR",
  to: "INR",
  conversionMultiple: 75,
  quantity: 10000,
  totalCalculatedAmount: 750000,
  port: 8001,
}

You can see that the port numbers in the two responses are different.

Summary

We have now created two microservices and established communication between them.

Image

We are using Ribbon to distribute load between the two instances of Forex Service.

However, we are hardcoding the urls of both instances of FS in CCS. That means every time there is a new instance of FS, we would need to change the configuration of CCS. Thats not cool.

In the next part, we will use Eureka Naming Server to fix this problem.

Next Steps

Continue the Microservice Series - Microservices with Spring Boot

What to Learn Next?

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