Rest with Spring Part-3 (Microservices)

What is microservice ?

It is an architectural style
Structures an application as a collection of loosely coupled Services
REST
Services are well choosen deployable unit
Cloud Enabled

How an Microservices Architecture looks like ?

Advantages of Using Microservices Architecture

New Technology and Process Adaption
Dynamic Scaling
Faster Release Cycle

Challenges with Microservices

Bonded Context
Configuration Management
Dynamic Scale up and Scale Down (Load Balancing)
Visibility (Common logging and monitoring)
Pack of cards (Fault Taulerant)

Spring Cloud

Spring Cloud provides tools for developers to quickly build some of the common patterns in distributed systems.
Coordination of distributed systems leads to boiler plate patterns, and using Spring Cloud developers can quickly stand up services and applications that implement those patterns.
They will work well in any distributed environment, including the developer's own laptop

For more details click https://projects.spring.io/spring-cloud/

Solutions in Spring Cloud for Microservices challenges

Problems	Solution
Configuration Management	Spring cloud config server
Dynamic Scale Up and Down	Naming Server (Eureka) Ribbon (Client Side Load Balancing) Feign (Easier Rest Client)
Visibility and Monitoring	Zipkin Distributed Tracing Netflix API Gateway
Fault Talerance	Hystrix

Microservices we will gonna create

CurrencyCalculationService

CurrencyExchangeService

LimitsService

Spring Cloud Config Server

CurrencyCalculationService

CurrencyExchangeService

LimitsService

Spring Cloud Config Server

Git

Setting up limits service

Step 1: Go to https://start.spring.io/ and generate a spring boot project with gradle with the below mention dependencies

Step 2:

Download the project from start.spring.io and extract the zip
Create an empty project in intellij Idea and import limits-service gradle project as module

Step 3:

Introduce following properties in application.properties

spring.application.name=limits-service

limits-service.minimum=9
limits-service.maximum=999

Step 4:

Create the following files in your project

Configuration
LimitsConfigurationController
LimitsConfiguration

Note : code for the files above is in the further slides

package com.springcloud.demo.limitsservice;

public class LimitsConfiguration {
    private int maximum;
    private int minimum;

    public int getMaximum() {
        return maximum;
    }

    public void setMaximum(int maximum) {
        this.maximum = maximum;
    }

    public int getMinimum() {
        return minimum;
    }

    public void setMinimum(int minimum) {
        this.minimum = minimum;
    }

    public LimitsConfiguration(int maximum, int minimum) {
        this.maximum = maximum;
        this.minimum = minimum;
    }
}

package com.springcloud.demo.limitsservice;

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

@Component
@ConfigurationProperties("limits-service")
public class Configuration {
    private int minimum;
    private int maximum;

    public int getMinimum() {
        return minimum;
    }

    public void setMinimum(int minimum) {
        this.minimum = minimum;
    }

    public int getMaximum() {
        return maximum;
    }

    public void setMaximum(int maximum) {
        this.maximum = maximum;
    }
}

package com.springcloud.demo.limitsservice;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class LimitsConfigurationController {

    @Autowired
    Configuration configuration;

    @GetMapping("/limits")
    LimitsConfiguration helloWorld(){
        return new LimitsConfiguration(configuration.getMinimum(),configuration.getMaximum());

    }
}

Exercise 1

Implement the limits service as shown in slide

Setting up Spring Cloud Config Server

Step 1 : Create the spring boot project with gradle with the dependencies shown below on start.spring.io

Step 2 :

Download and extract the project on your local system. Once you have extracted project then add it as module in your existing project

Step 3 :

Set the following values in application.properties file of spring-cloud-config-server

spring.application.name=spring-cloud-config-server
server.port=8888

spring.cloud.config.server.git.uri=<git-url-containing-properties-file>

Note : Enable Config server by placing @EnableConfigServer at the top of SpringCloudConfigServerApplication.java

In the git repo which you have added limits-service.properties file with the following value

Setting up git for spring cloud config server

limits-service.minimum=9
limits-service.maximum=999

Now hit http://localhost:8888/limits-service/default

You must get the properties which you have configured in the above git repo

Note: url name is related to properties filename

Environment specific configuration

For environment specific configuration you just need to add hyphen with Environment Name i.e limits-service-qa.properties and the properties available in this file will be available on the following url:

http://localhost:8888/limits-service/qa

Connecting limits-service to spring-cloud-config-server

Rename application.properties file in limits-service to bootstrap.properties and add the following properties to it

spring.application.name=limits-service

spring.cloud.config.uri=http://localhost:8888/

Run both applications i.e limits-service and spring-cloud-config-server and hit

http://localhost:8080/limits/

You will see the default values from spring cloud config server

Note : The file is picked on the bases of spring.application.name whose value in this case is limits-service so limits-service.properties will be picked

Configure profiles for Limits service

In order to configure the profile for limits service add the line below in boostrap.properties

spring.profiles.active=qa

Note : if the value is not set in the specified profile's properties file then default value will be picked

Exercise 2

Implement the Spring cloud config server as shown in slides

Setting up currency exchange service

Step 1:

Create a Spring boot project gradle project with the dependencies shown below

Step 2 :

After downloading and extracting the currency exchange service import it in Intellij idea with other microservices and set the following values in application.properties

spring.application.name=currency-exchange-service
server.port=8000

Step 3 :

Include the following files in the currency-exchange-service

CurrencyExchangeController.java
ExchangeValue.java

Code for the files is in the next 2 slides

package com.springcloud.demo.currencyexchangeservice;

import java.math.BigDecimal;

public class ExchangeValue {

    private Long id;
    private String from;
    private String to;
    private BigDecimal conversionMultiple;

    public ExchangeValue() {
    }

    public ExchangeValue(Long id, String from, String to, BigDecimal conversionMultiple) {
        this.id = id;
        this.from = from;
        this.to = to;
        this.conversionMultiple = conversionMultiple;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getFrom() {
        return from;
    }

    public void setFrom(String from) {
        this.from = from;
    }

    public String getTo() {
        return to;
    }

    public void setTo(String to) {
        this.to = to;
    }

    public BigDecimal getConversionMultiple() {
        return conversionMultiple;
    }

    public void setConversionMultiple(BigDecimal conversionMultiple) {
        this.conversionMultiple = conversionMultiple;
    }
}

package com.springcloud.demo.currencyexchangeservice;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

import java.math.BigDecimal;

@RestController
public class CurrencyExchangeController {

    @GetMapping("/currency-exchange/from/{from}/to/{to}")
    public ExchangeValue retrieveExchangeValue(@PathVariable String from,@PathVariable String to){
        return new ExchangeValue(1000L,from,to, BigDecimal.valueOf(20));
    }

}

Run Mulitple instances of Currency Exchange service

Create a copy of existing configuration and set VM options for it to -Dserver.port=8001

Introduce port int type instance variable in ExchangeValue and set the port value in CurrencyExchangeController in the following way:

 exchangeValue.setPort(Integer.parseInt(environment.getProperty("local.server.port")));

Exercise 3

Implement currency-exchange-service as shown in slides and run multiple instances of it.

Setting up currency conversion

Create a spring boot project with gradle which contains the dependency shown in the image below from https://start.spring.io/

Step 2:

In application.properties of currency exchange service add the following lines

spring.application.name=currency-conversion-service
server.port=8100

Step 3:

Include the following files in currency convert module:

CurrencyConversionController.java
CurrencyConversion.java

Code for the files is in the next to slides

package com.springcloud.demo.currencyconversionservice;

import java.math.BigDecimal;

public class CurrencyConversion {

    private Long id;
    private String from;
    private String to;
    private BigDecimal conversionMultiple;
    private int port;
    private BigDecimal totalCalculatedAmount;

    public CurrencyConversion() {
    }

    public CurrencyConversion(Long id, String from, String to, BigDecimal conversionMultiple) {
        this.id = id;
        this.from = from;
        this.to = to;
        this.conversionMultiple = conversionMultiple;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getFrom() {
        return from;
    }

    public void setFrom(String from) {
        this.from = from;
    }

    public String getTo() {
        return to;
    }

    public void setTo(String to) {
        this.to = to;
    }

    public BigDecimal getConversionMultiple() {
        return conversionMultiple;
    }

    public void setConversionMultiple(BigDecimal conversionMultiple) {
        this.conversionMultiple = conversionMultiple;
    }

    public int getPort() {
        return port;
    }

    public void setPort(int port) {
        this.port = port;
    }

    public BigDecimal getTotalCalculatedAmount() {
        return totalCalculatedAmount;
    }

    public void setTotalCalculatedAmount(BigDecimal totalCalculatedAmount) {
        this.totalCalculatedAmount = totalCalculatedAmount;
    }
}

package com.springcloud.demo.currencyconversionservice;


import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.core.env.Environment;
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;
import org.springframework.web.client.RestTemplate;

import java.math.BigDecimal;
import java.util.HashMap;
import java.util.Map;

@RestController
public class CurrencyConversionController {

    @Autowired
    Environment environment;

    @GetMapping("/currency-converter/from/{from}/to/{to}/quantity/{quantity}")
    public CurrencyConversion covertCurrency(@PathVariable String from,
                                             @PathVariable String to,
                                             @PathVariable BigDecimal quantity){
        Map<String,String> pathVariables = new HashMap<>();
        pathVariables.put("from",from);
        pathVariables.put("to",to);
        ResponseEntity<CurrencyConversion>  responseEntity=new RestTemplate()
                .getForEntity("http://localhost:8000/currency-exchange/from/{from}/to/{to}",
                        CurrencyConversion.class,pathVariables);
        CurrencyConversion currencyConversion= responseEntity.getBody();
        currencyConversion.setPort(Integer.parseInt(environment.getProperty("local.server.port")));
        currencyConversion.setTotalCalculatedAmount(quantity.multiply(currencyConversion.getConversionMultiple()));
        return currencyConversion;
    }
}

Exercise 4

Implement currency-conversion-service which will use currency exchange service as shown in slides

Using feign Rest Client for Service invocation

Feign is a declarative Rest Service client.
It makes writing rest service client easier.
Feign provides integration with ribbon which is client side load balancer

Include the following dependency in build.gradle of currency-conversion-service

compile('org.springframework.cloud:spring-cloud-starter-openfeign')

Enable feign in Spring Boot application by Marking the application class of currency conversion service with

@EnableFeignClients("<package name to scan>") 
i.e

@EnableFeignClients("com.springcloud.demo.currencyconversionservice")

Now we need to create a proxy interface class for currency exchange service

package com.springcloud.demo.currencyconversionservice;

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;

@FeignClient(name = "currency-exchange-service" ,url = "localhost:8000")
public interface CurrencyExchangeServiceProxy {

    @GetMapping("/currency-exchange/from/{from}/to/{to}")
    CurrencyConversion retrieveExchangeValue(@PathVariable("from") String from,
        @PathVariable("to") String to);
}

Now add one more action ConvertCurrencyFeign to CurrencyConversionController as shown below:

package com.springcloud.demo.currencyconversionservice;


import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.core.env.Environment;
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;
import org.springframework.web.client.RestTemplate;

import java.math.BigDecimal;
import java.util.HashMap;
import java.util.Map;

@RestController
public class CurrencyConversionController {

    @Autowired
    Environment environment;

    @Autowired
    CurrencyExchangeServiceProxy proxy;

    @GetMapping("/currency-converter/from/{from}/to/{to}/quantity/{quantity}")
    public CurrencyConversion covertCurrency(@PathVariable String from,
                                             @PathVariable String to,
                                             @PathVariable BigDecimal quantity){
        Map<String,String> pathVariables = new HashMap<>();
        pathVariables.put("from",from);
        pathVariables.put("to",to);
        ResponseEntity<CurrencyConversion>  responseEntity=new RestTemplate()
                .getForEntity("http://localhost:8000/currency-exchange/from/{from}/to/{to}",
                        CurrencyConversion.class,pathVariables);
        CurrencyConversion currencyConversion= responseEntity.getBody();
        currencyConversion.setPort(Integer.parseInt(environment.getProperty("local.server.port")));
        currencyConversion.setTotalCalculatedAmount(quantity.multiply(currencyConversion.getConversionMultiple()));
        return currencyConversion;
    }

    @GetMapping("/currency-converter-feign/from/{from}/to/{to}/quantity/{quantity}")
    public CurrencyConversion covertCurrencyFeign(@PathVariable String from,
                                             @PathVariable String to,
                                             @PathVariable BigDecimal quantity){
        CurrencyConversion currencyConversion= proxy.retrieveExchangeValue(from,to);
        currencyConversion.setPort(Integer.parseInt(environment.getProperty("local.server.port")));
        currencyConversion.setTotalCalculatedAmount(quantity.multiply(currencyConversion.getConversionMultiple()));
        return currencyConversion;
    }
}

Exercise 5

Use feign client to consume endpoint of currency-exchange-service from currency-conversion-service

Setting up client side load balancing with Ribbon

Existing problem is that one instance of CurrencyConversionService can talk to one instance of CurrencyExchangeService.
Ribbon comes to rescue here. It distributes the load to different instances.

CurrencyCalculationService

NamingServer

CurrencyExchangeService1

Ribbon

CurrencyExchangeService2

CurrencyExchangeService3

In order to get started with ribbon first you need to import the dependency of ribbon in build.gradle of currency-conversion-service as follows:

compile('org.springframework.cloud:spring-cloud-starter-netflix-ribbon')

Mark CurrencyExchangeServiceProxy with RibbonClient annotation as shown below

package com.springcloud.demo.currencyconversionservice;

import org.springframework.cloud.netflix.ribbon.RibbonClient;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;

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

    @GetMapping("/currency-exchange/from/{from}/to/{to}")
    CurrencyConversion retrieveExchangeValue(@PathVariable("from") String from, @PathVariable("to") String to);
}

Now we need to add following property in the application.properties of currency-conversion-service

spring.application.name=currency-conversion-service
server.port=8100
currency-exchange-service.ribbon.listOfServers=http://localhost:8000,http://localhost:8001

Need of a naming server

In the previous example we have hardcoded the names of the 2 instances of currency-exchange-service into application.properties of currency-conversion service.

Now if we need to add another instance of currency-exchange-service to ribbon then we need to add the url of that instance in application.properties file of currency-conversion-service.

In order to avoid making hardcoded changes application.properties file we will use Eureka naming server.

Setting up the eureka server

Step 1 : Create Spring boot Gradle project with the dependencies mentioned the image below

Step 2 : Enable the Eureka Server

package com.springcloud.demo.netflixeurekanamingserver;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;

@SpringBootApplication
@EnableEurekaServer
public class NetflixEurekaNamingServerApplication {

	public static void main(String[] args) {
		SpringApplication.run(NetflixEurekaNamingServerApplication.class, args);
	}
}

Step 3 : Set the following properties value in application properties file for eureka naming server

spring.application.name=netflix-eureka-naming-server
server.port=8761

eureka.client.register-with-eureka=false
eureka.client.fetch-registry=false

Run the application and hit http://localhost:8761/

You should be able to see UI of Eureka naming server

Connecting currency-conversion-service to eureka naming server

Step 1: Add the following dependency in currency-conversion-service

compile('org.springframework.cloud:spring-cloud-starter-netflix-eureka-client')

Step 2: Enable Client discovery through annotaion @EnableClientDiscovery

package com.springcloud.demo.currencyconversionservice;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.openfeign.EnableFeignClients;

@SpringBootApplication
@EnableFeignClients(basePackages ={"com.springcloud.demo.currencyconversionservice"} )
@EnableDiscoveryClient
public class CurrencyConversionServiceApplication {

	public static void main(String[] args) {
		SpringApplication.run(CurrencyConversionServiceApplication.class, args);
	}
}

Step 3: Add the eureka server url in application.properties file of currency-conversion-service

spring.application.name=currency-conversion-service
server.port=8100
eureka.client.service-url.default-zone=http://localhost:8761/eureka
currency-exchange-service.ribbon.listOfServers=http://localhost:8000,http://localhost:8001

Now first run the eureka server and then currency-conversion-service. Now hit http://localhost:8761/ you should be able to see that currency-coversion-service is registered as instance in eureka naming server

Connecting currency-exchange-service to Eureka naming server

Step 1: Add the following dependency in currency-exchange-service

compile('org.springframework.cloud:spring-cloud-starter-netflix-eureka-client')

Step 2: Enable Client discovery through annotaion @EnableClientDiscovery

package com.springcloud.demo.currencyexchangeservice;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;

@SpringBootApplication
@EnableDiscoveryClient
public class CurrencyExchangeServiceApplication {

	public static void main(String[] args) {
		SpringApplication.run(CurrencyExchangeServiceApplication.class, args);
	}
}

Step 3: Add the eureka server url in application.properties file of currency-exchange-service

spring.application.name=currency-exchange-service
server.port=8000
eureka.client.service-url.default-zone=http://localhost:8761/eureka

Now run the 2 instances of currency- exchange-service and both the instances should be registered in Eureka naming server

Distributing calls using Eureka and Ribbon

comment line currency-exchange-service.ribbon.listOfServers

in application.properties and now try to run currency-conversion-service to observe the ports form currency-exchange-service

spring.application.name=currency-conversion-service
server.port=8100
eureka.client.service-url.default-zone=http://localhost:8761/eureka

#currency-exchange-service.ribbon.listOfServers=http://localhost:8000,http://localhost:8001

API Gateways

API Gateways are required to intercept calls between microservices

Common Functionality of API Gateways

Authentication, Authorization and Security
Rate Limits
Fault Tolerance

Setting up Zuul API Gateway

Enable Zuul proxy and Discover Clients

package com.springcloud.demo.netflixzuulapigatewayserver;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.netflix.zuul.EnableZuulProxy;
import org.springframework.cloud.netflix.zuul.EnableZuulServer;

@EnableZuulProxy
@EnableDiscoveryClient
@SpringBootApplication
public class NetflixZuulApiGatewayServerApplication {

	public static void main(String[] args) {
		SpringApplication.run(NetflixZuulApiGatewayServerApplication.class, args);
	}
}

Values in application.properties for Zuul API Gateway

spring.application.name=netflix-zuul-api-gateway-server
server.port=8765
eureka.client.service-url.default-zone=http://localhost:8761/eureka

Create the following Bean of Zuul Filter as follows :

package com.springcloud.demo.netflixzuulapigatewayserver;

import com.netflix.zuul.ZuulFilter;
import com.netflix.zuul.context.RequestContext;
import com.netflix.zuul.exception.ZuulException;
import org.springframework.stereotype.Component;

import javax.servlet.http.HttpServletRequest;
import java.util.logging.Logger;

@Component
public class ZuulLoggingFilter extends ZuulFilter {
    private  Logger logger= Logger.getLogger(this.getClass().toString());
    @Override
    public String filterType() {
        return "pre";
    }

    @Override
    public int filterOrder() {
        return 1;
    }

    @Override
    public boolean shouldFilter() {
        //business logic goes here
        return true;
    }

    @Override
    public Object run() throws ZuulException {
        HttpServletRequest httpServletRequest =
                RequestContext.getCurrentContext().getRequest();
        logger.info("httpServletRequest>>>"+httpServletRequest);
        logger.info("request uri"+httpServletRequest.getRequestURI());
        return null;
    }
}

Endpoint to hit in order to execute endpoint through API gateway

API-Gateway-App-URL/Application-name/Application-URL

Following is the example where we are hitting endpoint of currency-conversion-service with the help of API Gateway

localhost:8765/currency-conversion-service/currency-converter-feign/from/USD/to/INR/quantity/22000

Setting up Zuul between microservices invocation

In our case we are hitting currency-exchange-service with currency-conversion-service and we want to invoke the API call via API gateway. We need to do the following changes in CurrencyExchangeServiceProxy.java

package com.springcloud.demo.currencyconversionservice;

import org.springframework.cloud.netflix.ribbon.RibbonClient;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;

//@FeignClient(name = "currency-exchange-service" )
@FeignClient(name = "netflix-zuul-api-gateway-server" )
@RibbonClient(name = "currency-exchange-service")
public interface CurrencyExchangeServiceProxy {

//    @GetMapping("/currency-exchange/from/{from}/to/{to}")
    @GetMapping("/currency-exchange-service/currency-exchange/from/{from}/to/{to}")
    CurrencyConversion retrieveExchangeValue(@PathVariable("from") String from, @PathVariable("to") String to);
}

Sequency in which applications should be run

netflix-eureka-naming-server
netflix-zuul-api-gateway-server
currency-exchange-service
currency-conversion-service

Now if you hit localhost:8765/currency-conversion-service/currency-converter-feign/from/USD/to/INR/quantity/22000

you will be able to see logs for both currency-conversion-service and currency-exchange service

Understanding the need of Spring Cloud Bus

Include following configuration in application.properties file of limits-service.

Create One more instance of limits-service with port 8081.
Run both the instances of limits service and hit the /limits endpoint to get the minimum and maximum value.
Now change the value of maximum and minimum in git repository.
In order to reflect the update value in limits service we need to hit the following endpoint POST for both the instances

<hostname:port>/actuator/refresh

For every instance we need to hit this endpoint

management.endpoints.web.exposure.include=*