kubeages/gnomes-demo

Spring Cloud Services demo

gnomes-demo

This a simple microservice(ish) application consisted of three microservices

• gnomes-data: REST data endpoint that generates random data points (Eureka)

• aggregation: Aggregate data from data endpoint, does in a reactive manner using rx-java (Eureka, Hystrix)

• api: An [API-Gateway](http://microservices.io/patterns/apigateway.html) that serves the datapoint using charts (Eureka,Zuul)

Building

gradle build

Creating services

You will need a circuit breaker and a service registry to run this apps:

cf cs p-circuit-breaker-dashboard standard hystrix

cf cs p-service-registry standard registry

Pushing the apps

You can push all apps at once using the parent manifest file. There’s a manifest on each microservice as well to push individually

cf push -f manifest.yml

How to demo this

data-services project

You can demo how simple it is to bind to a service registry:

@SpringBootApplication
@EnableDiscoveryClient
@ServiceScan
public class DataApplication {

    public static void main(String[] args) {
        SpringApplication app = new SpringApplication(DataApplication.class);
        app.run(args);
    }


}

If you curl the enpoint of this application:

curl http://$cfdomain/gnomes/data

{
data: 19.878341758728503
}

Outputs random data to simulate a data service

aggregation project

This project aggregates the results from the data project, it simulates two calls protected by hystrix.

If you curl the endpoint:

curl http://$cfdomain/aggregation/aggregate

{
profit: 116.68136286795357,
gnomes: 15.65027543673633
}

The clients:

@Component
public class GnomesClient {

    @Autowired
    private RestTemplate template;

    private Double lastValue = 0.0; (1)

   @HystrixCommand(fallbackMethod = "defaultValue",
            commandProperties = {
                    @HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds", value = "5000"),
                    @HystrixProperty(name = "execution.isolation.strategy", value = "SEMAPHORE")
            })
    public Observable<Map<String,Double>> gnomesData(){

       return new ObservableResult<Map<String, Double>>() {
           @Override
           public Map<String, Double> invoke() {
               Map<String,Double> response = template.getForObject("http://gnomes-data/data",Map.class, Collections.singletonMap("base",10)); (2)
               Double data = response.get("data");
               lastValue = data;
               return Collections.singletonMap("gnomes",data);
           }
       };


    }

    public Map<String,Double> defaultValue(){
        return Collections.singletonMap("gnomes",lastValue);
    }

}

1. This acts as a "cache" that fallback method will always return the last read value when the circuit opens

2. Note the usage of ribbon here, no call to an URI but instead a service id on eureka

The aggregation service:

@Component
public class AggregationService {

    @Autowired
    private GnomesClient gnomesClient;
    @Autowired
    private ProfitClient profitClient;

    public Observable<Map<String,Double>> aggregate(){ (1)
        return Observable.zip(gnomesClient.gnomesData(), profitClient.profitData(), (d1,d2) -> {
            Map<String,Double> zip = new HashMap<String, Double>();
            zip.putAll(d1);
            zip.putAll(d2);
            return zip;
        });
    }
}

1. Combines two observables from the results of the clients into one

Point your browser to the hystrix dashboard:

The api endpoint

• Point your browser to the api application:

The application charts the data from aggregation at a 5 requests/second rate

• Point your browser to hystrix again to show the metrics

Stop the gnomes-data application:

cf stop gnomes-data

You can demonstrate the resilience of your app, instead of the client throwing an error due a service being down, it actually plots the last read value from the service (fallback method)

Show that hystrix is on open state

Restart your gnomes-data

cf start gnomes-data

• When you go back to the api you will see that after a few seconds the data flow is restored.