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PORTS MAPPING

API-Gateway ----------------> Port 9191

Department-Service ---------> Ports: 8080, 8082

Employee-Service -----------> Port 8081

Organization-Service -------> Port 8083

Config-Server --------------> Port 8888 (Spring Cloud Config)

Service Registry -----------> Port 8761 (Eureka Server)

Organization-Service -------> Port 8083

React-Frontend -------------> Port 3000

Zipkin Server ---------> Port 9411

Commands to create the services

curl -G https://start.spring.io/starter.zip -d dependencies=web,mysql,jpa,lombok -d type=maven-build -d groupId=info.josealonso -d artifactId=employee-service -o employee-service.zip

curl -G https://start.spring.io/starter.zip -d dependencies=web,mysql,jpa,lombok -d type=maven-build -d groupId=info.josealonso -d artifactId=department-service -o department-service.zip

Testing a service with httpie

http -v get http://localhost:8083/api/v1/organizations/test or http -v get localhost:8083/api/v1/organizations/test or http -v get :8083/api/v1/organizations/test

saveOrganization

http -v post :8083/api/v1/organizations id:=7 organizationName=ABCd organizationCode=ABC_23Y
organizationDescription="........"

getOrganizationByCode

http -v get :8083/api/v1/organizations/ABC_23Y

Spring Boot Actuator

Only /info and /health endpoints are enabled by default.

Service Registry and Discovery

  • We need a mechanism to call other services without hardcoding their hostnames or port numbers.
  • Since instances may come up and go anytime, we need some automatic service registration and discovery mechanism.

The @EnableEurekaClient annotation was removed in spring cloud 2022.0.0.

Run multiple instances of the same microservice

To run another instance of department-service

BASIC APPROACH

  • cd department-service
  • java -jar -Dserver.port=8082 target/department-service-0.0.1-SNAPSHOT.jar

LOAD BALANCER APPROACH

Eureka Server provides the Spring Cloud load balancer library.

API Gateway

It provides a unified interface for a set of microservices so that clients no need to know the microservices internals. It centralizes cross-cutting concerns like security, monitoring or rate limiting.

  • Route request.
  • Load balancing.
  • Security. Spring Cloud provides Spring Cloud Gateway to create an API Gateway.

Config Server

Refresh Use Case

We do not want to restart the microservice whenever we change the configuration file.

Solution ---> call the Spring Boot Actuator /refresh API to reload the updated values from the Config Server.

Spring Cloud Bus

Instead of calling the Refresh API for each microservice, a message broker is connected to the event generated by the API. All the microservices are subscribed to this event.

  Message ----------->       n       --------> Config ------> Git repository  
  Broker                microservices          Server

Install and run RabbitMQ

docker pull rabbitmq:3.11.0

docker run --rm -it -p 5672:5672 rabbitmq:3.11.0

Testing it

GET http://localhost:8080/message GET http://localhost:8081/users/message

A POST call to http://localhost:8080/actuator/busrefresh will tell the message broker to broadcast the configuration changes to the respecting microservices.

Distributed Tracing

Track the complete request across all the microservices, from start to end. Keep track of how much time the microservice will take to process the request. Trace id is the same for each request. Span id is the same for each microservice.

Spring Cloud Sleuth was used in Spring Boot 2.x projects.

The Spring Cloud Sleuth dependency would be added to the following projects: api-gateway, department-service and employee-service.

As a result, the traces would have the format:

  [Service name, Trace id, Span id]

Visualize Trace information

Zipkin is a widely used library.

Mechanisms or patterns implemented by Resilience4j

  • Fallback method
  • Circuit breaker 3 states:
    • closed ---> allows to flow the request between two microservices.
    • open -----> that circuit is closed during a configurable time limit.
    • half open ---> only certain number of calls are allowed. It goes to open state or to closed state based on the response.
  • Retry
  • Rate Limiter