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Apache HTrace is a tracing framework intended for use with distributed systems written in java. Since version 3.1.3, Apache CXF fully supports integration with Apache HTrace, both on client side and server side. This section gives a complete overview on how distributed tracing support is supported in JAX-RS applications built on top of Apache CXF.

Distributed Tracing with Apache HTrace in Nutshell

Distributed tracing, first described by Google in Dapper, a Large-Scale Distributed Systems Tracing Infrastructure paper became increasingly important topic these days. With microservices (aka SOA) gaining more and more adoption, the typical applications are built using dozens or even hundreds of small, distributed pieces. The end-to-end traceability of the requests (or any kind of work performed on user's behalf) is hard task to accomplish, particularly taking into account asyncronous or/and concurrent invocations. Apache HTrace is inspired by Dapper, a Large-Scale Distributed Systems Tracing Infrastructure paper and essentially is a full-fledged distributed tracing framework.

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Another two important concepts in context of distributed tracing are span receivers and samplers. Essentially, all spans (including start/stop time, key/value annotations, timelines, ..) should be persisted (or collected) somewhere. Span receiver is a collector within a process that is the destination of spans when a trace is running (it could be a console, local file, data store, ...). Apache HTrace provides span receivers for Apache HBase, Apache Flume and Twitter Zipkin. From other side, samplers allow to control the frequency of the tracing (all the time, never, probability driven, ...). Using the sampler is the way to minimize tracing overhead (or just amount of traces) by limiting them to particular conditions.

Distributed Tracing in Apache CXF using Apache HTrace

Apache CXF is a very popular framework for building services and web APIs. No doubts, it is going to play even more important role in context of microservices architecture letting developers to quickly build and deploy individual JAX-RS/JAX-WS services. As it was just mentioned before, distributed tracing is an essential technique to monitor the application as whole, breaking the request to individual service traces as it goes through and crosses the boundaries of threads, processes and machines.

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