Service Discovery with Spring Cloud Eureka

Now just talk about different concept of configuration -
                                                                Eureka

also called passive service discovery

Task:

• Build and Run Spring cloud Eureka Server
• Build and Run and Configure a Eureka Client

Service Discovery

➤Microservices architecture results in large number of inter-service calls

➥this is challenging to configure

➤ How can one application easily find all of the other runtime dependencies

-manual configuration - not good

➤Service discovery provides a single 'lookup service'

clients register themselves,discover other registrants

• what could be possible solutions?
• Eureka,Consul,Zookeeper,SmartStack etc

Eureka -Service Discovery Server and client 

➤Eureka provides a look up server

➥generally made highly available by multiple copies

➥copies replicate state of registered server

➤"Client" services register with Eureka

➥ provides metadata on host,port,health indicator ,URL ,etc.

➤Client services send heartbeat to Eureka

➥ Eureka removes services without any heartbeat

Creating Eureka Server

➤Multiple Eureka server should be running simultaneously  

    ➥otherwise you will get many warnings in the log

    there are share states and eureka server communicate with each        other to share state

    ➥provides highly availability 

➤ Each server should know url of each others

 - can be provided by config server

- One server(JAR),multiple profiles

                             

                                                      Shared states

                                                          ⬈

Eureka Server ⟷  Eureka server    ⟷     Eureka server

         🔻                        🔻                             🔻

Region: us east       Region: Us west          Region: EU

Create a Spring Cloud Eureka Server and Client

➤ Create a new Spring Boot application.

➤ from spring cloud discovery select eureka server

below is the genrated pom for the same.

pom.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>2.1.8.RELEASE</version>

<relativePath/> <!-- lookup parent from repository -->

</parent>

<groupId>com.demo</groupId>

<artifactId>lab-eureka-server</artifactId>

<version>0.0.1-SNAPSHOT</version>

<name>lab-eureka-server</name>

<description>spring config server</description>

<properties>

<java.version>1.8</java.version>

<spring-cloud.version>Greenwich.SR3</spring-cloud.version>

</properties>

<dependencies>

<dependency>

<groupId>org.springframework.cloud</groupId>

<artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>

</dependency>

<dependency>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-test</artifactId>

<scope>test</scope>

</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>

</project>

➤Save an application.yml (or properties) file in the root of your classpath (src/main/resources recommended). Add the following key / values (use correct YAML formatting):

application.yml
---
# This default profile is used when running a single instance completely standalone:
spring:
  profiles: default
server:

  port: 8010 

➤Save a bootstrap.yml  file in the root of your classpath. Add the following key / values (use correct YAML formatting):

bootstrap.yml

---
spring:
  application:

    name: lab-eureka-server


➤Add @EnableEurekaServer to the Application class. Save. Start the server. Temporarily ignore the warnings about running a single instance (i.e. connection refused, unable to refresh cache, backup registry not implemented, etc.). Open a browser to http://localhost:8010 to see the server running.