Talk about netflix's EurekaHttpClient

sequence

This article mainly studies EurekaHttpClient of netflix

EurekaHttpClient

eureka-client-1.8.8-sources.jar!/com/netflix/discovery/shared/transport/EurekaHttpClient.java

public interface EurekaHttpClient {

    EurekaHttpResponse<Void> register(InstanceInfo info);

    EurekaHttpResponse<Void> cancel(String appName, String id);

    EurekaHttpResponse<InstanceInfo> sendHeartBeat(String appName, String id, InstanceInfo info, InstanceStatus overriddenStatus);

    EurekaHttpResponse<Void> statusUpdate(String appName, String id, InstanceStatus newStatus, InstanceInfo info);

    EurekaHttpResponse<Void> deleteStatusOverride(String appName, String id, InstanceInfo info);

    EurekaHttpResponse<Applications> getApplications(String... regions);

    EurekaHttpResponse<Applications> getDelta(String... regions);

    EurekaHttpResponse<Applications> getVip(String vipAddress, String... regions);

    EurekaHttpResponse<Applications> getSecureVip(String secureVipAddress, String... regions);

    EurekaHttpResponse<Application> getApplication(String appName);

    EurekaHttpResponse<InstanceInfo> getInstance(String appName, String id);

    EurekaHttpResponse<InstanceInfo> getInstance(String id);

    void shutdown();
}

You can see that this client interface defines some low level rest apis of eureka server, including register, cancel, sendHeartBeat, statusUpdate, getApplications, etc.

EurekaHttpClientDecorator

eureka-client-1.8.8-sources.jar!/com/netflix/discovery/shared/transport/decorator/EurekaHttpClientDecorator.java

public abstract class EurekaHttpClientDecorator implements EurekaHttpClient {

    public enum RequestType {
        Register,
        Cancel,
        SendHeartBeat,
        StatusUpdate,
        DeleteStatusOverride,
        GetApplications,
        GetDelta,
        GetVip,
        GetSecureVip,
        GetApplication,
        GetInstance,
        GetApplicationInstance
    }

    public interface RequestExecutor<R> {
        EurekaHttpResponse<R> execute(EurekaHttpClient delegate);

        RequestType getRequestType();
    }

    protected abstract <R> EurekaHttpResponse<R> execute(RequestExecutor<R> requestExecutor);

    //......
}

EurekaHttpClientDecorator wraps EurekaHttpClient by defining an abstract method execute(RequestExecutor<R> requestExecutor)

Subclass of EurekaHttpClientDecorator

The classes inherited from EurekaHttpClientDecorator are as follows, all in the com.netflix.discovery.shared.transport.decorator package

• MetricsCollectingEurekaHttpClient
• RedirectingEurekaHttpClient
• RetryableEurekaHttpClient
• SessionedEurekaHttpClient

EurekaHttpClientFactory(top level)

eureka-client-1.8.8-sources.jar!/com/netflix/discovery/shared/transport/EurekaHttpClientFactory.java

/**
 * A top level factory to create http clients for application/eurekaClient use
 *
 * @author Tomasz Bak
 */
public interface EurekaHttpClientFactory {

    EurekaHttpClient newClient();

    void shutdown();

}

This is the factory high-level interface of EurekaHttpClient, which defines newClient() and shutdown() methods

Implementation class of EurekaHttpClientFactory

• RetryableEurekaHttpClient eureka-client-1.8.8-sources.jar!/com/netflix/discovery/shared/transport/decorator/RetryableEurekaHttpClient.java

    public static EurekaHttpClientFactory createFactory(final String name,
                                                        final EurekaTransportConfig transportConfig,
                                                        final ClusterResolver<EurekaEndpoint> clusterResolver,
                                                        final TransportClientFactory delegateFactory,
                                                        final ServerStatusEvaluator serverStatusEvaluator) {
        return new EurekaHttpClientFactory() {
            @Override
            public EurekaHttpClient newClient() {
                return new RetryableEurekaHttpClient(name, transportConfig, clusterResolver, delegateFactory,
                        serverStatusEvaluator, DEFAULT_NUMBER_OF_RETRIES);
            }

            @Override
            public void shutdown() {
                delegateFactory.shutdown();
            }
        };
    }

Created is a client wrapped by RetryableEurekaHttpClient

• MetricsCollectingEurekaHttpClient eureka-client-1.8.8-sources.jar!/com/netflix/discovery/shared/transport/decorator/MetricsCollectingEurekaHttpClient.java

    public static EurekaHttpClientFactory createFactory(final EurekaHttpClientFactory delegateFactory) {
        final Map<RequestType, EurekaHttpClientRequestMetrics> metricsByRequestType = initializeMetrics();
        final ExceptionsMetric exceptionMetrics = new ExceptionsMetric(EurekaClientNames.METRIC_TRANSPORT_PREFIX + "exceptions");
        return new EurekaHttpClientFactory() {
            @Override
            public EurekaHttpClient newClient() {
                return new MetricsCollectingEurekaHttpClient(
                        delegateFactory.newClient(),
                        metricsByRequestType,
                        exceptionMetrics,
                        false
                );
            }

            @Override
            public void shutdown() {
                shutdownMetrics(metricsByRequestType);
                exceptionMetrics.shutdown();
            }
        };
    }

Created is a client wrapped by MetricsCollectingEurekaHttpClient

• EurekaHttpClients eureka-client-1.8.8-sources.jar!/com/netflix/discovery/shared/transport/EurekaHttpClients.java

    static EurekaHttpClientFactory canonicalClientFactory(final String name,
                                                          final EurekaTransportConfig transportConfig,
                                                          final ClusterResolver<EurekaEndpoint> clusterResolver,
                                                          final TransportClientFactory transportClientFactory) {

        return new EurekaHttpClientFactory() {
            @Override
            public EurekaHttpClient newClient() {
                return new SessionedEurekaHttpClient(
                        name,
                        RetryableEurekaHttpClient.createFactory(
                                name,
                                transportConfig,
                                clusterResolver,
                                RedirectingEurekaHttpClient.createFactory(transportClientFactory),
                                ServerStatusEvaluators.legacyEvaluator()),
                        transportConfig.getSessionedClientReconnectIntervalSeconds() * 1000
                );
            }

            @Override
            public void shutdown() {
                wrapClosable(clusterResolver).shutdown();
            }
        };
    }

What is created is the client wrapped by RedirectingEurekaHttpClient, RetryableEurekaHttpClient, SessionedEurekaHttpClient and the original EurekaHttpClient is created by TransportClientFactory

TransportClientFactory(low level)

eureka-client-1.8.8-sources.jar!/com/netflix/discovery/shared/transport/TransportClientFactory.java

/**
 * A low level client factory interface. Not advised to be used by top level consumers.
 *
 * @author David Liu
 */
public interface TransportClientFactory {

    EurekaHttpClient newClient(EurekaEndpoint serviceUrl);

    void shutdown();

}

As mentioned in the comments, it is not recommended for high-level consumers, it is a low-level api

TransportClientFactory implementation class

• JerseyEurekaHttpClientFactory eureka-client-1.8.8-sources.jar!/com/netflix/discovery/shared/transport/jersey/JerseyEurekaHttpClientFactory.java
• JerseyRemoteRegionClientFactory eureka-core-1.8.8-sources.jar!/com/netflix/eureka/transport/JerseyRemoteRegionClientFactory.java
• RestTemplateTransportClientFactory spring-cloud-netflix-eureka-client-2.0.0.RC1-sources.jar!/org/springframework/cloud/netflix/eureka/http/RestTemplateTransportClientFactory.java

The above three are implemented by special classes, and the following are implemented by anonymous classes

• RedirectingEurekaHttpClient
• EurekaServerHttpClients
• Jersey1TransportClientFactories
• MetricsCollectingEurekaHttpClient

summary

Netflix's eureka's interface for httpClient is EurekaHttpClient, and its factory methods are mainly classified into top level EurekaHttpClientFactory and low level TransportClientFactory.

• At the top level, a series of packaging is mainly carried out through the decorator mode. For example, EurekaHttpClients creates clients that are wrapped by RedirectingEurekaHttpClient, RetryableEurekaHttpClient, and SessionedEurekaHttpClient.
• In the case of low levle, it is mainly the implementation of the underlying http remote call, netflix provides the Jersey-based version, and spring cloud provides the RestTemplate-based version.

doc

• EurekaHttpClient