"Welcome To Ashok IT"				
			                    "Spring Boot and MicroServices"
                                             Topic : MicroServices Communication
                                             Date  : 01/07/2025
                                                (Session - 78)                               
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Feign Client / Open Feign:
=========================
* It is also one type of Rest Client given by Netflix Organization.

* Earlier Netfilx Organization used the Feign client for their Internal projects for communication between microservices.

* In the last two years Netflix organization stopped the feign client Development because They moved this Project Netflix open       source   software Community that why name of Feign client got changed to open Feign.

* Spring provided abstraction layer on open Feign under sub project of "Spring-cloud" module.

* Spring cloud open Feign is an declartive type of developing Rest Client.

* As programmer we just need to develop Feign clients as simple "interfaces" and we no need to worry implementation of this         interfaces   will be taken care Feign.

* we need to add the following starter to work with Feigh client i.e.,openfeign

* When working with spring cloud open feign we are using main two anotations

    1) @EnableFeignClients  >>>>> It will scan & identify all the Feign clients available in our project.

    2) @FeignClient("name") >>>>> This annotation is used to represent interface as Feign Client.


* UpStream & DownStream  
                                DownStream
   Customer Microservices  ---------------------> Address Microservices
                                 UpStream
                           <-------------------- Address Microservices

Example
=======
AddressClient.java
==================
package com.ashokit.feign;

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

import com.ashokit.response.AddressResponse;
import com.ashokit.response.AddressResponseList;

@FeignClient(url= "${address.service.name.url}",name="Address-Service")
public interface AddressClient {
	
	@GetMapping(value = "/")
	public ResponseEntity<AddressResponseList> fetchAllAddresses();
	
	@GetMapping(value = "/customer/{customerId}")
	public ResponseEntity<AddressResponse> fetchAddressByCustomerId(@PathVariable("customerId") Integer customerId);

}

application.properties
======================
#server port changing
server.port=9977

#Database Configuration
spring.datasource.driver-class-name=oracle.jdbc.driver.OracleDriver
spring.datasource.url=jdbc:oracle:thin:@localhost:1521:xe
spring.datasource.username=system
spring.datasource.password=manager

#Hibernate Configuration
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true

#Application name configuration
spring.application.name=Customer-Service

#Address Microservices Configuration
address.service.name.url=http://localhost:9966/api/address/

Service Discovery
=================
* Typically in microservice development we do have multiple microservices as programmer it is very hard to remember everything about      Microservice.
    
* To overcome the problem the service registry will maintain all microservices related information i.e.,API URL's,How many Instances are           running for that service,Information about Service,Service is up or down and also used for communicating from  one microservice to another        Microservices using Service Names instead of Hard coded URL's.

* Spring cloud provides the multiple Service discovery API's such as Eureka,ZooKeeper,Consul,Cloud foundry etc.,

* As part of this ServiceDiscovery we will creating three spring boot applications

    1) Service Registry Application : To Track all the Microservices in our project i.e.,Eureka Server Application

    2) Customer-Service : This Application need to be registered as one of Eureka Client

    3) Address-Service  : This Application need to be registered as one of Eureka Client.

Developing the Service Registry Application(40_MicroServices_ServiceDiscovery_App)
==================================================================================
1) Create the Spring Boot Application with Below straters

     * Spring Web 

     * Eureka Server

2) Add the following annotation i.e.,@EnableEurekaServer top of main class 

Application.java
================
package com.ashokit;

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

//Activates the Eureka Server and its configuration
@EnableEurekaServer 
@SpringBootApplication
public class Application {

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

3) Add the eureka server configuration entries in application.yml/application.properties

application.properties
======================
#Default Port number for Eureka Server
server.port=8761

#Disabling the Registration of this project with Eureka Server
eureka.client.register-with-eureka=false

#Disabling the Discovery operation of this project with Eureka Server
eureka.client.fetch-registry=false

NOTE: 
=====
**** By Default Eureka Server always run on port number is 8761

4) Run the Spring Boot Applcation and open your browser and hit below URL
 
    http://localhost:8761  >>>>>>>>>>>>>>> We can see the Eureka Server Dashboard Screen

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