A Spring Boot project demonstrating the usage of:
- Ribbon (Load Balancer)
- Eureka (Service Discovery)
- Feign (Declarative Rest Client)
In this project you can see how to use Spring Boot and have a client side load balancer. We will use two services:
- LoadBalance_Caller
- LoadBalance_Responder
Both services will register themselves on Eureka server:
- LoadBalancer_Eureka
Once all are up and running, you can see in action how the load balancer can route the incoming requests to the registered services.
First start the LoadBalancer_Eureka. This is your Service Discovery server.
Both our services (LoadBalance_Caller, LoadBalance_Responder) needs to register themselves on the Discovery server. So start those services after you have started the Eureka server.
Check file: application.properties
We have the following:
# Application Info
spring.application.name=YkaravEurekaServer
server.port=9000
# Eureka Server Info
eureka.client.serviceUrl.defaultZone=http://localhost:9000/eureka/
eureka.client.register-with-eureka=false
eureka.client.fetch-registry=false
Explanation of the properties:
| Property | Explanation |
|---|---|
| spring.application.name | The name of our application |
| server.port | The port on which our Eureka server is running |
| eureka.client.serviceUrl.defaultZone | Set default zone in case there are many Eureka servers |
| eureka.client.register-with-eureka | Set if Eureka server will also be registered as client |
| eureka.client.fetch-registry | Set if Eureka server will register itself on the service registry |
We alse have to set the application as Eureka server.
Use annotation @EnableEurekaServer on class
LoadBalanceEurekaApplication
And that's it! Our Eureka server is ready.
Check file: application.properties
We have the following:
# Application Info
spring.application.name=responder
server.port=8082
# Eureka Server Info
eureka.instance.hostname=localhost
eureka.client.serviceUrl.defaultZone=http://localhost:9000/eureka/
Explanation of the properties:
| Property | Explanation |
|---|---|
| spring.application.name | The name of our application |
| server.port | The port on which our Eureka server is running |
| eureka.instance.hostname | The hostname of our eureka instance |
| eureka.client.serviceUrl.defaultZone | URL of the eureka server |
We have to register our service so it can be traced by our Eureka server.
On class LoadBalanceResponderApplication, use annotiation @EnableDiscoveryClient to activate the Netflix Eureka DiscoveryClient implementation.
Check file: application.properties
We have the following:
# Application Info
spring.application.name=caller
server.port=8081
# Eureka Server Info
eureka.instance.hostname=localhost
eureka.client.serviceUrl.defaultZone=http://localhost:9000/eureka/
Explanation is the same as on LoadBalancer_Responder.
We have to register our service so it can be traced by our Eureka server.
On class LoadBalanceCallerApplication, use annotiation @EnableDiscoveryClient to activate the Netflix Eureka DiscoveryClient implementation.
We are going to use Feign so we also have to activate it. Use annotation @EnableFeignClients.
Let's see class PersonCallerFeignCtrl
@RestController
public class PersonCallerFeignCtrl {
@Autowired
ResponderProxy proxy;
@RequestMapping("/caller/feign/findAll")
public List<Person> findAll(){
return proxy.persons();
}
}When the user calls
http://localhost:8081//caller/feign/findAll
he is actually calling for:
http://localhost:8082/getPersons
How is it done? This is the way:
The method findAll returns the result of the persons method of instance proxy.
Looking at class ResponderProxy
@FeignClient(name="RESPONDER" )
@RibbonClient(name="RESPONDER")
public interface ResponderProxy {
@RequestMapping("/getPersons")
public List<Person> persons();
}We can see that method persons maps to request: /getPersons. And proxy instance is basically calling for service with name responder. Which is already registered on our Eureka server.