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reactive-http-client

Provides a reactive HTTP client builder for service/client interaction.

Builds a fully functional resilient client over a reactive interface against an HTTP (HTTPS, HTTP/2) service endpoint.

Assuming we have the following API interface:

interface ServiceEndpoint {
    @retrofit2.http.GET("getpath/{id}")
    Mono<Response> getData(@Path("id") String id);

    @retrofit2.http.POST("postpath")
    Mono<Response> postData(@Body Request request);
    
    @retrofit2.http.DELETE("delete/{id}")
    Mono<Void> delete(@Path("id") String id);
}

Then building a full-fledged reactive and resilient HTTP client for it would be:

ServiceEndpoint client = RetrofitServiceClientBuilder.createOver(ServiceEndpoint.class, BASE_URL).buildClient();

The built client will have the following features built-in:

  • connection pooling
  • circuit-breaker
  • bulkhead
  • metrics
  • retry
  • request-tracing
  • call-log

See com.hotels.molten.http.client.RetrofitServiceClientBuilder for more details.

Configuration

The client built is highly configurable:

ServiceEndpoint client = RetrofitServiceClientBuilder.createOver(ServiceEndpoint.class, BASE_URL)
    .expectedLoad(ExpectedLoad.builder()
        .peakResponseTime(Duration.ofMillis(800))
        .averageResponseTime(Duration.ofMillis(20))
        .peakRequestRatePerSecond(10)
        .averageRequestRatePerSecond(5)
        .build())          
    .recovery(RecoveryConfiguration.builder()
        .responsiveness(Duration.ofSeconds(10))
        .failureThreshold(25)
        .slowCallDurationThreshold(50)
        .slowCallRateThreshold(75)
        .build())
    .connectionSettings(ConnectionSettings.builder()
        .timeout(Duration.ofSeconds(1))
        .keepAliveIdle(Duration.ofMinutes(10))
        .maxLife(Duration.ofMinutes(15))
        .retryOnConnectionFailure(false)
        .build())
    .maxRetries(2)
    .objectMapper(customObjectMapper) // Jackson object mapper
    .metrics(meterRegistry) // micrometer registry
    .groupId("customGroupId") // isolates circuits, bulkheads, metrics and call logs
    .requestTracking(customRequestTracking) // to propagate certain data with every request
    .httpTracing(httpTracing) // Zipkin Brave http tracing
    .buildClient();

See default settings and additional details in com.hotels.molten.http.client.RetrofitServiceClientBuilder and com.hotels.molten.http.client.RetrofitServiceClientConfiguration.

HTTP client implementation

The default underlying HTTP client being used is OkHTTP. Reactor-netty based HTTP client is also supported, however, it is still experimental. To switch to reactor-netty client add it to classpath

<dependency>
  <groupId>io.projectreactor.netty</groupId>
  <artifactId>reactor-netty</artifactId>
</dependency>

and enable it for selected or all clients via system properties:

  • MOLTEN_HTTP_CLIENT_DEFAULT_TYPE=[OKHTTP|NETTY] to set client type globally
  • MOLTEN_HTTP_CLIENT_TYPE_fully_qualified_Api=[OKHTTP|NETTY] to set client type for a specific client only (e.g. fully.qualified.Api in this case)

Protobuf

The client supports Protobuf for serializing request and deserializing responses. This can be enabled using builder.usingProtobuf(). Be sure to add protobuf as dependency:

<dependency>
  <groupId>com.google.protobuf</groupId>
  <artifactId>protobuf-java</artifactId>
</dependency>

Metrics

If meterRegistry is set then several metrics are automatically registered along with the final configuration of the client. See com.hotels.molten.http.client.RetrofitServiceClientBuilder documentation for details.

Preconfigured Grafana dashboards are available for:

See com.hotels.molten.core.metrics.MetricsSupport how to switch between hierarchical and dimensional metrics.

Certificates

Custom HTTPS certificates are supported when com.hotels.molten.http.client.SSLContextConfiguration is provided. See com.hotels.molten.http.client.RetrofitServiceClientBuilder#customSSLContext for details.