Boot

Spring Boot Microservices Java Example

Joel Patrick LlosaJuly 22nd, 2019Last Updated: July 7th, 2022

26 2,189 15 minutes read

In this article, we will explain Spring Boot Microservices with Java through examples.

Microservices is popular because it allows large systems to be composed of smaller systems. Think of it as the single responsibility principle.

The smaller systems have a single responsibilty to the large system. In the monolithic approach, all the smaller systems are bunched up to make up one large system or one large appplication. The microservices approach breaks the large system into smaller chunks.

You can also check this tutorial in the following video:

1. Introduction

This article assumes that you know your way around Eclipse. You are familiar with Maven and Spring. This project has been created using Eclipse Oxygen so all instructions are based on this IDE. Download the example code, load it into Eclipse or your favorite IDE and let’s walk through the code.

1. Introduction

2. Spring Boot Microservices

2.1. Prerequisites
2.2. Download
2.3. Setup
2.4.IDE

3.POM

4.Eureka Server

5.Addition Server

6.Subtraction Server

7.Web Server

8.What are Microservices?

9.Accessing the Microservices

10.Running the Spring Boot Microservices Example

11.Microservices benefits and drawbacks

12.When to choose microservices instead of monolithic architecture

13.Summary

14.Download the Source Code

2. Spring Boot Microservices

This is a simple Spring Boot Microservices example. This web application does nothing more but an arithmetic service. An arithmetic calculator served in a microservice approach. The diagram below shows our two microservices, Addition Server and Subtraction Server. The servers need to find each other so they need to register to the discovery server called Eureka. Once the Web Server finds the micro service, it can then send requests. In this example, the Web Server sends RESTful requests. When the Web Server receives the response it then serves the result to the browser.

2.1 Prerequisites

Java 8 or 9 is required on the linux, windows or mac operating system. Maven 3.6.1 is required for building the spring boot application.

2.2 Download

You can download Java 8 can be downloaded from the Oracle web site . Apache Maven 3.6.1 can be downloaded fromApache site. Spring framework latest releases are available from the spring website.

2.3 Setup

You can set the environment variables for JAVA_HOME and PATH. They can be set as shown below:

Java Setup

JAVA_HOME="/desktop/jdk1.8.0_73"
export JAVA_HOME
PATH=$JAVA_HOME/bin:$PATH
export PATH

The environment variables for maven are set as below:Environment Setup for Maven

Maven Setup

JAVA_HOME=”/jboss/jdk1.8.0_73″
export M2_HOME=/users/bhagvan.kommadi/Desktop/apache-maven-3.6.1
export M2=$M2_HOME/bin
export PATH=$M2:$PATH

2.4 IDE

2.4.1 Eclipse Oxygen Setup

The ‘eclipse-java-oxygen-2-macosx-cocoa-x86_64.tar’ can be downloaded from the eclipse website. The tar file is opened by double click. The tar file is unzipped by using the archive utility. After unzipping, you will find the eclipse icon in the folder. You can move the eclipse icon from the folder to applications by dragging the icon.

2.4.2 Launching IDE

Eclipse has features related to language support, customization, and extension. You can click on the eclipse icon to launch eclipse. The eclipse screen pops up as shown in the screenshot below:

You can select the workspace from the screen which pops up. The attached image shows how it can be selected.

Microservices Java - IntelliJ vs Eclipse — Eclipse Workspace

You can see the eclipse workbench on the screen. The attached screenshot shows the Eclipse project screen.

Microservices Java - Eclipse Workbench — Eclipse Workbench

Java Hello World class prints the greetings. The screenshot below is added to show the class and execution on the eclipse.

Microservices Java - Java Hello — Java Hello

3. POM

The important parts of the POM are the following:

spring-boot-starter-parent – provide default configurations for our Spring Boot project
spring-boot-starter – setup Spring Boot
spring-boot-starter-web – setup Spring MVC and REST, use Embedded Tomcat
spring-boot-starter-thymeleaf – use Thymeleaf templating engine
spring-cloud-starter – setup Spring Cloud
spring-cloud-starter-netflix-eureka-server – Eureka for service registration
spring-cloud-dependencies – use the Finchley.RELEASE

4. Eureka Server

The code for the registration server is only a few lines. It really is this short.

EurekaServer.java

EurekaServer

package com.javacodegeeks.example.registration;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;
@SpringBootApplication
@EnableEurekaServer
public class EurekaServer {
    public static void main(String[] args) {
        System.setProperty("spring.config.name", "eureka-server");
        SpringApplication.run(EurekaServer.class, args);
    }
}

@SpringBootApplication is a convenience annotation that is equivalent to declaraing @Configuration, @EnableAutoConfiguration, and @ComponentScan. The @EnableEurekaServer spins up a registry server that other applications can talk to. Line 11 tells Spring Boot to look for the file eureka-server.properties for its configuration.

eureka-server.properties

eureka.instance.hostname=localhost
eureka.client.registerWithEureka=false
eureka.client.fetchRegistry=false
 
server.port=1111
 
spring.thymeleaf.enabled=false

We’ll be running the Eureka Server on port 1111. The default is 8761. Indicating registerWithEureka as false stops the server from registering itself. We would register ourself when we are running multiple discory servers. Open up a command prompt and let’s run the Eureka Server. But first we must compile our project, execute mvn clean package. After successful compilation, run java -jar target/spring-boot-microservices-0.0.1-SNAPSHOT.jar eureka and you should see some standard Spring logging output in the console. Open your web browser, access http://localhost:1111/ and you should see something like below:

Microservices Java - Eureka Server — Eureka Server

5. Addition Server

This server provides the addition service. It simply adds two numbers.

AdditionServer.java

package com.javacodegeeks.example.rest.addition;
 
import java.util.logging.Logger;
 
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.context.annotation.ComponentScan;
 
@EnableAutoConfiguration
@EnableDiscoveryClient
@ComponentScan
public class AdditionServer {
 
    protected Logger logger = Logger.getLogger(AdditionServer.class.getName());
 
    public static void main(String[] args) {
        System.setProperty("spring.config.name", "addition-server");
 
        SpringApplication.run(AdditionServer.class, args);
    }
}

@EnableAutoConfiguration defines this as a Spring Boot application. The @EnableDiscoveryClient enables service registration and discovery. The server registers itself with the discovery server provided in the configuration file. The registration with the discovery server makes this a microservice.

addition-server.properties

# Spring properties
spring.application.name=addition-service
spring.freemarker.enabled=false
spring.thymeleaf.cache=false
spring.thymeleaf.prefix=classpath:/addition-server/templates/
 
error.path: /error
 
# HTTP Server
server.port: 2222
 
eureka.client.serviceUrl.defaultZone=http://localhost:1111/eureka/
eureka.client.instance.leaseRenewalIntervalInSeconds=5
management.endpoints.web.exposure.include='*'

As the cofiguration states, this microservice is named as addition-service. It will listen on port 2222. It will use the discovery server at http://localhost:1111/eureka/. leaseRenewalIntervalInSeconds for now is set to five but this is not recommended in production. By default the client refresh time is thirty seconds. By now you should have packaged the application. In case you have not, execute mvn clean package. After successful compilation, run java -jar target/spring-boot-microservices-0.0.1-SNAPSHOT.jar addition and you should see some standard Spring logging output in the console. To check if your microservices is up and running open your web browser, access http://localhost:2222/ and you should see a message saying “Addition Server Microservice is running”. Alternatively, you can access http://localhost:1111/eureka/apps/addition-service/ and you’ll receive an XML of the details of the addition service. Or you could check the Eureka Server page and the addition-service should be listed under instances currently registered with Eureka.

Below are additional source files required to run the Addition Server.

HomeController.java

package com.javacodegeeks.example.rest.addition;
 
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
 
@Controller
public class HomeController {
 
    @RequestMapping("/")
    public String home() {
        return "index";
    }
 
}

The above controller simply directs requests to the root resource to index.html. All thymeleaf templates are found in src/main/resources. This particular template is located in src/main/resources/addition-server/templates.

AdditionController.java

package com.javacodegeeks.example.rest.addition;
 
import java.util.logging.Logger;
 
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
 
@RestController
public class AdditionController {
 
    protected Logger logger = Logger.getLogger(AdditionController.class
            .getName());
 
    @RequestMapping("/add")
    public String doAdd(@RequestParam(defaultValue="0") String addend1,
            @RequestParam(defaultValue="0") String addend2) {
 
        int augend1 = Integer.valueOf(addend1);
        int augend2 = Integer.valueOf(addend2);
        int sum = augend1 + augend2;
 
        return "{\"addend1\":\"" + addend1 + "\", \"addend2\":\"" + addend2 + "\", \"sum\": \"" + sum + "\"}";
    }
}

The doAdd method handles requests made on /add. It retrieves the parameters and adds them. It then returns a JSON string.

6. Subtraction Server

This server provides the subtraction service. It simply deducts a number from another number.

SubtractionServer.java

package com.javacodegeeks.example.rest.subtraction;
 
import java.util.logging.Logger;
 
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.context.annotation.ComponentScan;
 
@EnableAutoConfiguration
@EnableDiscoveryClient
@ComponentScan
public class SubtractionServer {
    protected Logger logger = Logger.getLogger(SubtractionServer.class.getName());
 
    public static void main(String[] args) {
        System.setProperty("spring.config.name", "subtraction-server");
 
        SpringApplication.run(SubtractionServer.class, args);
    }
}

The SubtractionServer.java is similar to the AdditionServer.java code. The only difference is the configuration.

subtraction-server.properties

# Spring properties
spring.application.name=subtraction-service
spring.freemarker.enabled=false
spring.thymeleaf.cache=false
spring.thymeleaf.prefix=classpath:/subtraction-server/templates/
 
error.path: /error
 
# HTTP Server
server.port: 3333
 
eureka.client.serviceUrl.defaultZone=http://localhost:1111/eureka/
eureka.client.instance.leaseRenewalIntervalInSeconds=5
management.endpoints.web.exposure.include='*'

As the cofiguration states, this microservice is named as subtraction-service. It will listen on port 3333. It will use the discovery server at http://localhost:1111/eureka/. Run java -jar target/spring-boot-microservices-0.0.1-SNAPSHOT.jar subtraction and you should see some standard Spring logging output in the console. To check if your microservices is up and running open your web browser, access http://localhost:3333/ and you should see a message saying “Subtraction Server Microservice is running”. Or you could check the Eureka Server page and the subtraction-service should be listed under instances currently registered with Eureka. You can also access http://localhost:1111/eureka/apps/subtraction-service/ to get XML details of the service just like the addition server.

Below are additional source files required to run the Subtraction Server.

HomeController.java

package com.javacodegeeks.example.rest.subtraction;
 
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
 
@Controller
public class HomeController {
 
    @RequestMapping("/")
    public String home() {
        return "index";
    }
 
}

SubtractionController.java

package com.javacodegeeks.example.rest.subtraction;
 
import java.util.logging.Logger;
 
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
 
@RestController
public class SubtractionController {
    protected Logger logger = Logger.getLogger(SubtractionController.class
            .getName());
 
    @RequestMapping("/subtract")
    public String doSubtract(@RequestParam(defaultValue="0") String minuend,
            @RequestParam(defaultValue="0") String subtrahend) {
 
        int m = Integer.valueOf(minuend);
        int s = Integer.valueOf(subtrahend);
        int difference = m - s;
 
        return "{\"minuend\":\"" + minuend + "\", \"subtrahend\":\"" + subtrahend + "\", \"difference\": \"" + difference + "\"}";
    }
}

The doSubtract method handles requests made on /subtract. It retrieves the parameters and subtracts them. It then returns a JSON string.

7. Web Server

This server serves web pages to the browser. This server uses the microservices. Since this article is about microservices, we will not go into detail on how to serve web content with Spring MVC.

WebServer.java

package com.javacodegeeks.example.web;
 
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.web.client.RestTemplate;
 
@SpringBootApplication
@EnableDiscoveryClient
@ComponentScan(useDefaultFilters = false)
public class WebServer {
 
    public static final String ADDITION_SERVICE_URL = "http://addition-service";
 
    public static final String SUBTRACTION_SERVICE_URL = "http://subtraction-service";
 
    public static void main(String[] args) {
        System.setProperty("spring.config.name", "web-server");
        SpringApplication.run(WebServer.class, args);
    }
 
    @LoadBalanced
    @Bean
    RestTemplate restTemplate() {
        return new RestTemplate();
    }
 
    @Bean
    public WebAdditionService additionService() {
        return new WebAdditionService(ADDITION_SERVICE_URL);
    }
 
    @Bean
    public WebArithmeticController additionController() {
        return new WebArithmeticController(additionService(), subtractionService());
    }
 
    @Bean
    public WebSubtractionService subtractionService() {
        return new WebSubtractionService(SUBTRACTION_SERVICE_URL);
    }
 
    @Bean
    public HomeController homeController() {
        return new HomeController();
    }
}

@SpringBootApplication is a convenience annotation that is equivalent to declaraing @Configuration, @EnableAutoConfiguration, and @ComponentScan. The @EnableDiscoveryClient enables service registration and discovery. The @ComponentScan(useDefaultFilters = false) indicates whether automatic detection of classes annotated with @Component, @Repository, @Service, or @Controller should be enabled.

@LoadBalanced marks RestTemplate< to be configured to use a LoadBalancerClient. This means the RestTemplate bean will be auto-configured by Spring Cloud to use a custom HttpRequestClient that uses Netflix Ribbon to do the microservices lookup. Ribbon is also a load-balancer. If you have multiple instances of a service available, Ribbon picks one for you.

web-server.properties

spring.application.name=web-service
spring.freemarker.enabled=false
spring.thymeleaf.cache=false
spring.thymeleaf.prefix=classpath:/web-server/templates/
 
error.path=/error
 
server.port:4444
 
eureka.client.serviceUrl.defaultZone:http://localhost:1111/eureka
eureka.instance.leaseRenewalIntervalInSeconds:5
    
management.endpoints.web.exposure.include='*'
 

As the cofiguration states, the application name is web-service. It will listen on port 4444. It will use the discovery server at http://localhost:1111/eureka/. Open up a command prompt and run java -jar target/spring-boot-microservices-0.0.1-SNAPSHOT.jar web. After some standard Spring logging, you should be able to access the web server at http://localhost:4444/. By this time, we have four open command prompts running four servers simultaneously. The web server page looks like the one below.

Microservices Java - Web Server — Web Server

And your Eureka server will have all three services registered as you can see below.

Spring Boot Microservices Example Eureka List

Below are additional source files required to run the Web Server.

HomeController.java

package com.javacodegeeks.example.web;
 
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
 
@Controller
public class HomeController {
 
    @RequestMapping("/")
    public String home() {
        return "index";
    }
 
}

WebArithmeticController.java

package com.javacodegeeks.example.web;
 
import java.util.logging.Logger;
 
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
 
@Controller
public class WebArithmeticController {
    @Autowired
    protected WebAdditionService additionService;
 
    @Autowired
    protected WebSubtractionService subtractionService;
 
    protected Logger logger = Logger.getLogger(WebArithmeticController.class
            .getName());
 
    public WebArithmeticController(WebAdditionService additionService, WebSubtractionService subtractionService) {
        this.additionService = additionService;
        this.subtractionService = subtractionService;
    }
 
    @RequestMapping("/add")
    public String doAdd(@RequestParam(defaultValue="0") String addend1,
            @RequestParam(defaultValue="0") String addend2,
            Model model) {
 
        String sum = additionService.add(addend1, addend2);
 
        logger.info("Sum: " + sum);
        model.addAttribute("json", sum);
 
        return "sum";
    }
 
    @RequestMapping("/subtract")
    public String doSubtract(@RequestParam(defaultValue="0") String minuend,
            @RequestParam(defaultValue="0") String subtrahend,
            Model model) {
 
        String difference = subtractionService.subtract(minuend, subtrahend);
 
        logger.info("Difference: " + difference);
        model.addAttribute("json", difference);
 
        return "difference";
    }
}

The doAdd method handles requests made on /add. It retrieves the parameters and passes it to the additionService object which was automatically injected by Spring. It then returns the sum.html template. The doSubtract method handles requests made on /subtract. It retrieves the parameters and passes it to the subtractionService object which was automatically injected by Spring. It then returns the difference.html template. The service classes are discussed in the next section.

8. What are Microservices?

Microservices are based on the single responsibility principle. The principle is related to grouping things that are impacted by the change. Single responsibility is related to SOLID principles. Robert C.Martin created this principle which states a single unit will have only one responsibility. Microservices architecture helps in creating applications that can be created and managed as different components or services. The components or services are loosely coupled and deployed separately. Every service performs a different type of work and interacts with others using API. Microservices help in creating resilience in the architecture. These services have routing like traditional Unix pipes thorough endpoints for information flow. Spring Boot has features to create and deploy microservices on the cloud and on the enterprise premises.

For example, an eCommerce application can have web and mobile user interfaces talking to different microservices such as user login, user authorization, product catalog, order management, shopping cart, payment, and delivery. Docker is used as a container for each of the services. Docker-compose helps in the orchestration of the services which are containerized.

Microservices are built using Spring Boot, Spark, Jersey, Restlet, Restx, Swagger, and Dropwizard frameworks. Microservices are based on design principles such as Domain Driven Design, Failure Isolation, Continuous delivery, Decentralization, and DevOps. Each microservice can be independently deployed, updated, replaced, and scaled. (DURS)

References related to Micro services:

9. Accessing the Microservices

WebAdditionService.java

package com.javacodegeeks.example.web;
 
import java.util.logging.Logger;
 
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;
 
@Service
public class WebAdditionService {
 
    @Autowired
    @LoadBalanced
    protected RestTemplate restTemplate;
 
    protected String serviceUrl;
 
    protected Logger logger = Logger.getLogger(WebAdditionService.class
            .getName());
 
    public WebAdditionService(String serviceUrl) {
        this.serviceUrl = serviceUrl.startsWith("http") ? serviceUrl
                : "http://" + serviceUrl;
    }
 
    public String add(String addend1, String addend2) {
        return restTemplate.getForObject(serviceUrl + "/add?addend1={addend1}&addend2={addend2}", String.class, addend1, addend2);
    }
}

WebSubtractionService.java

package com.javacodegeeks.example.web;
 
import java.util.logging.Logger;
 
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;
 
@Service
public class WebSubtractionService {
    @Autowired
    @LoadBalanced
    protected RestTemplate restTemplate;
 
    protected String serviceUrl;
 
    protected Logger logger = Logger.getLogger(WebSubtractionService.class
            .getName());
 
    public WebSubtractionService(String serviceUrl) {
        this.serviceUrl = serviceUrl.startsWith("http") ? serviceUrl
                : "http://" + serviceUrl;
    }
 
    public String subtract(String minuend, String subtrahend) {
        return restTemplate.getForObject(serviceUrl + "/subtract?minuend={minuend}&subtrahend={subtrahend}", String.class, minuend, subtrahend);
    }
}

The above classes are similar. Both are annotated with @Service. This indicates that the class is a service which is an operation offered as an interface that stands alone in the model, with no encapsulated state. This annotation serves as a specialization of @Component, allowing for implementation classes to be autodetected through classpath scanning. RestTemplate is load balanced as explained above. The serviceUrl is provided by the main program. The restTemplate returns a JSON string which is displayed by the web server.

10. Running the Spring Boot Microservices Example

Execute mvn clean package to create the fat jar. For conveniece, we have a fat jar whose start class is com.javacodegeeks.example.Main. Just provide the arguments eureka, addition, substraction, or web to run the respective servers.

Main.java

package com.javacodegeeks.example;
 
import com.javacodegeeks.example.registration.EurekaServer;
import com.javacodegeeks.example.rest.addition.AdditionServer;
import com.javacodegeeks.example.rest.subtraction.SubtractionServer;
import com.javacodegeeks.example.web.WebServer;
 
public class Main {
    public static void main(String[] args) {
 
        String serverName = "";
 
        switch (args.length) {
        case 2:
            System.setProperty("server.port", args[1]);
        case 1:
            serverName = args[0].toLowerCase();
            break;
 
        default:
            return;
        }
 
        if (serverName.equals("eureka")) {
            EurekaServer.main(args);
        } else if (serverName.equals("addition")) {
            AdditionServer.main(args);
        } else if (serverName.equals("subtraction")) {
            SubtractionServer.main(args);
        } else if (serverName.equals("web")) {
            WebServer.main(args);
        } else {
            System.out.println("Unknown server type: " + serverName);
        }
    }
}

It is easier to run the different applications by running them from the command line with different windows. It will be eaiser to see their log output.

java -jar target/spring-boot-microservices-0.0.1-SNAPSHOT.jar eureka – executes the eureka server
java -jar target/spring-boot-microservices-0.0.1-SNAPSHOT.jar addition – executes the addition server
java -jar target/spring-boot-microservices-0.0.1-SNAPSHOT.jar subtraction – executes the subtraction server
java -jar target/spring-boot-microservices-0.0.1-SNAPSHOT.jar web – executes the web server

11. Microservices benefits and drawbacks

Development is faster in the case of microservices as the units of code required for a service is lesser. Deployment can be done independently and scaling the application is easier in the Microservices case. Fault Isolation is better in the case of Microservices architecture. Fixes for the error can be deployed on a specific service without impacting other services. The choice of the technology stack is very easy as each service can be built using a different programming language for a specific requirement. Each service can be integrated into different types of data sources such as relational database, no SQL database, hierarchical database, and web services.

Microservices apps will have lesser merges and code conflicts. Each microservice will have its own repository. Communication across distributed services can be challenging if one of the services is down.Security can be another challenge across multiple services. Each technology stack requires a separate pipeline or workflow for deployment. The readability of the code is affected as the services are decoupled. Configuration of multiple microservices needs to be maintained which can be a challenge (for 100 microservices). DevOps and automation is the only way to deploy and manage these microservices. Centralized logging need to be there to isolate the issue specific to a microservice.

12. When to choose microservices instead of monolithic architecture

A complex application can be broken down into small services and components. Developing this complex app can be a good candidate for a microservice architecture style instead of a monolithic architecture style. The benefit of building using microservices style is in cost and scaling the application. The startup time of a monolithic application is higher compared to microservices-based applications.

Microservices are easy for development, deployment, and testing. Many of monolithic applications are complex for maintenance and upgrades. Microservices help in refactoring complex monolithic architecture based applications for better flexibility, security, and time to market. Microservices architecture embraces new technologies and integrates with legacy easily using web services and messaging approaches. The engineering team can easily get trained on different microservices as microservices are loosely coupled. Unit testing each service helps in a better quality of the overall application. Functional tests for each service will be helpful for overall integration testing of the microservices application. Failures can be handled easily by identifying the service which is causing the failure. Isolation of the problem and resolution is easy in the case of microservices application.

Large applications which are complex for implementation, deployment and upgrades are great candidates of refactoring using microservices architecture. Continuous integration and deployment is feasible using microservices. Reliability is higher as there is no single point of failure. Technology adaption is easier when implementing new microservice.

To start on a complex app, monolithic architecture style helps in creating a small application which has components and deployed as a single app. As new requirements come in and complexity grows, you see the need for microservices. Evolution of application functionality is better in the case of microservices.

13. Summary

In summary, the discovery server is started up first. Then the microservices and the web server register to the discovery server in order for them to find each other. Once the web server knows where to find the microservices, it can then issue RESTful requests to the microservices. The web server performs its task aided by the microservices. The process is made simple and easy with the help of Spring. Microservices architecture based applications can be developed by using Spring Boot. Multi Runtime microservices with a monolith application can be a good middle ground for Microservices architecture style.