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Wingtips - apache-http-client

Wingtips is a distributed tracing solution for Java based on the Google Dapper paper.

This module is a plugin extension module of the core Wingtips library and contains support for distributed tracing using Apache's HttpClient (minimum version 4.4 required).

Usage Examples

NOTES:

  • The ApacheHttpClientWithWingtipsComponentTest shows these features in action against a real running server (launched as part of the test).
  • More details can be found in the javadocs for the various classes found in this wingtips-apache-http-client module.

Instrumenting Apache HttpClient using WingtipsHttpClientBuilder

This is the preferred mechanism for integrating Wingtips tracing with Apache HttpClient. If you control the creation of the HttpClientBuilder that is used to generate HttpClients then use WingtipsHttpClientBuilder. If you don't control which HttpClientBuilder is used, then you will need to use the interceptor described in the next section.

WingtipsHttpClientBuilder builder = WingtipsHttpClientBuilder.create();
// ... call whatever builder methods you need to finish configuring the HttpClient

// Any HttpClient built from a WingtipsHttpClientBuilder will handle Wingtips tracing concerns.
HttpClient httpClient = builder.build();

// Execute requests - any request will have Wingtips tracing info automatically propagated on the request headers.
HttpResponse response = httpClient.execute(...);

Instrumenting Apache HttpClient using WingtipsApacheHttpClientInterceptor

Manual interceptor addition:

Note the following to have your Wingtips subspans fully surround any other interceptors included in your HttpClient requests:

  • The Wingtips request interceptor should be the first builder.addInterceptorFirst(...) added.
  • The Wingtips response interceptor should be the last builder.addInterceptorLast(...) added.
HttpClientBuilder builder = getBuilderFromSomewhere();
WingtipsApacheHttpClientInterceptor interceptor = new WingtipsApacheHttpClientInterceptor();

builder.addInterceptorFirst((HttpRequestInterceptor)interceptor);
       
// ... other builder setup

builder.addInterceptorLast((HttpResponseInterceptor)interceptor);

// Any HttpClient built from this builder will handle Wingtips tracing concerns.
HttpClient httpClient = builder.build();     

// Execute requests - any request will have Wingtips tracing info automatically propagated on the request headers.
HttpResponse response = httpClient.execute(...);

Semi-automated interceptor addition:

This semi-automated interceptor addition helper method is functionally equivalent to the manual interceptor addition above, except for the potential for other request interceptors (added before) or other response interceptors (added after) to not be surrounded by the optional subspan. If you want your Wingtips subspans to fully surround all interceptors then you either need to use the manual method described above, or use WingtipsHttpClientBuilder instead of this interceptor.

In many cases this helper method drawback is inconsequential and the semi-automated helper method works perfectly fine, however be aware of this issue in case you have interceptors that are time-consuming or need to interact with Wingtips in any way.

HttpClientBuilder builder = getBuilderFromSomewhere();

WingtipsApacheHttpClientInterceptor.addTracingInterceptors(builder);

// ... other builder setup

// Any HttpClient built from this builder will handle Wingtips tracing concerns.
HttpClient httpClient = builder.build();     

// Execute requests - any request will have Wingtips tracing info automatically propagated on the request headers.
HttpResponse response = httpClient.execute(...);

Feature details

This wingtips-apache-http-client module contains two classes to perform the same Wingtips tracing tasks. The two classes are:

  • WingtipsHttpClientBuilder - An extension of Apache's HttpClientBuilder that guarantees correct handling of Wingtips tracing concerns for any HttpClient built from it. This should be used instead of the interceptor described below if possible (i.e. when you control the creation of the HttpClientBuilder that is used to generate HttpClients).
  • WingtipsApacheHttpClientInterceptor - An implementation of both HttpRequestInterceptor and HttpResponseInterceptor. When properly configured on a HttpClientBuilder they can serve the same purpose as WingtipsHttpClientBuilder, however you have to be more careful in using them and certain exceptions can occur that cause the response interceptor to be skipped, leading to dangling spans and broken tracing, so WingtipsHttpClientBuilder is preferred when possible. This interceptor should only be used when you don't control the creation of the HttpClientBuilder that is used to generate HttpClients and you still want a best-effort attempt at tracing.

In either case, the following features are provided:

  • Optionally surround requests in a subspan. The subspan option defaults to on and is highly recommended since the subspans will provide you with timing info for your downstream calls separate from any parent span that may be active at the time the request executes, and includes useful metadata span tags about the request and response.
    • If the subspan option is enabled but there's no current span on the current thread when the request executes, then a new root span (new trace) will be created rather than a subspan. In either case the newly created span will have a Span.getSpanPurpose() of CLIENT since the span is for a client HTTP request.
    • By default ZipkinHttpTagStrategy and ApacheHttpClientTagAdapter will be used to name subspans and automatically tag them with useful tags based on the request and response. You can override which tag/naming strategy and adapter is used during creation of the WingtipsHttpClientBuilder or WingtipsApacheHttpClientInterceptor.
    • The Span.getSpanName() for the newly created span will be generated by an overridable getSubspanSpanName(HttpRequest) method. This method defers to the tag/naming strategy, with a reasonable fallback in case the tag/naming strategy comes up blank. You can override this getSubspanSpanName(HttpRequest) method if you want different logic and you can't (or don't want to) adjust the tag/naming strategy instead.
  • Whatever Wingtips Span is current at the time the request executes (subspan if the subspan option is on, or whatever was current on the thread if the subspan option is off) will be propagated in the request headers using the logic described by the B3/Zipkin spec.
    • This means that no tracing info will be propagated in the case where the subspan option is off and the thread executing your Apache HttpClient request does not have any current Wingtips span. Turning on the subspan option mitigates this as it guarantees there will be a span to propagate.

For further details on these classes please see their javadocs.

For general Wingtips information please see the base project README.md.

NOTE - org.apache.httpcomponents:httpclient dependency required at runtime

This module does not export any transitive Apache HttpClient dependencies to prevent version conflicts with whatever environment your project is running in.

This should not affect most users since this library is likely to be used in an environment where the httpclient dependency is already on the classpath at runtime, however if you receive class-not-found errors related to classes found in httpclient then you'll need to pull the org.apache.httpcomponents:httpclient dependency into your project. Library authors who wish to build on functionality in this module might need to do this.

This module was built using version 4.4.1 of httpclient, but other versions of Apache HttpClient should work fine, both older and newer.