Overview

OpenZipkin Brave is a distributed tracing implementation compatible with Twitter Zipkin backend services, written in Java. For quite a while OpenZipkin Brave offers a dedicated module to integrate with Apache CXF framework, namely brave-cxf3. However, lately the discussion had been initiated to make this integration a part of Apache CXF codebase so the CXF team is going to be responsible for maintaining it. As such, it is going to be available in upcoming 3.2.0 release under cxf-integration-tracing-brave module, with both client side and server side supported. This section gives a complete overview on how distributed tracing using OpenZipkin Brave could be integrated into JAX-RS / JAX-WS applications built on top of Apache CXF.

OpenZipkin Brave is inspired by the Twitter Zipkin and Dapper, a Large-Scale Distributed Systems Tracing Infrastructure paper and is a full-fledged distributed tracing framework. The section dedicated to Apache HTrace has pretty good introduction into distributed tracing basics. However, there are a few key differences between Apache HTrace and OpenZipkin Brave. In Brave every Span is associated with 128 or 64-bit long Trace ID, which logically groups the spans related to the same distributed unit of work. Within the process spans are collected by reporters (it could be a console, local file, data store, ...). OpenZipkin Brave provides span reporters for Twitter Zipkin and java.util.logging loggers.

Under the hood spans are attached to their threads (in general, thread which created the span should close it), the same technique employed by other distributed tracing implementations. However, what is unique is that OpenZipkin Brave distinguishes three different types of tracers:

• server tracer (com.github.kristofa.brave.ServerTracer)
• client tracer (com.github.kristofa.brave.ClientTracer)
• local tracer (com.github.kristofa.brave.LocalTracer)

Apache CXF integration uses client tracer to instantiate spans on client side (providers and interceptors) to demarcate send / receive cycle, server tracer on the server side (providers and interceptors) to demarcate receive / send cycle, while using local tracer for any spans instantiated within a process.

Distributed Tracing in Apache CXF using OpenZipkin Brave

The current integration of distributed tracing in Apache CXF supports OpenZipkin Brave (3.16+ release branch) in JAX-RS 2.x+ and JAX-WS applications, including the applications deploying in OSGi containers. From high-level perspective, JAX-RS 2.x+ integration consists of three main parts:

• TracerContext (injectable through @Context annotation)
• BraveProvider (server-side JAX-RS provider) and BraveClientProvider (client-side JAX-RS provider)
• BraveFeature (server-side JAX-RS feature to simplify OpenZipkin Brave configuration and integration)

Similarly, from high-level perspective, JAX-WS integration includes:

• BraveStartInterceptor / BraveStopInterceptor / BraveFeature Apache CXF feature (server-side JAX-WS support)
• BraveClientStartInterceptor / BraveClientStopInterceptor / BraveClientFeature Apache CXF feature (client-side JAX-WS support)

Apache CXF uses HTTP headers to hand off tracing context from the client to the service and from the service to service. Those headers are used internally by OpenZipkin Brave and are not configurable at the moment. The header names are declared in the BraveHttpHeaders class and at the moment include:

• X-B3-TraceId: 128 or 64-bit trace ID
• X-B3-SpanId: 64-bit span ID
• X-B3-ParentSpanId: 64-bit parent span ID

• X-B3-Sampled: "1" means report this span to the tracing system, "0" means do not

By default, BraveClientProvider will try to pass the currently active span through HTTP headers on each service invocation. If there is no active spans, the new span will be created and passed through HTTP headers on per-invocation basis. Essentially, for JAX-RS applications just registering BraveClientProvider on the client and BraveProvider on the server is enough to have tracing context to be properly passed everywhere. The only configuration part which is necessary are span reports(s) and sampler(s).

It is also worth to mention the way Apache CXF attaches the description to spans. With regards to the client integration, the description becomes a full URL being invoked prefixed by HTTP method, for example: GET http://localhost:8282/books. On the server side integration, the description becomes a relative JAX-RS resource path prefixed by HTTP method, f.e.: GET books, POST book/123