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README.md

02-logback-brave

This module is showcasing how to use some APIs from Brave.

How does it work?

TracingFactory

  • this factory is used in all examples in this project to create an instance of brave.Tracing
  • it first creates an instance of zipkin2.reporter.brave.AsyncZipkinSpanHandler for reporting spans to Tempo
  • then, it proceeds with Tracing.newBuilder() which is provided with sampling, naming and other options
  • brave.propagation.ThreadLocalCurrentTraceContext is created for propagating the trace context
  • this is where brave.context.slf4j.MDCScopeDecorator gets registered to take care of putting baggage into MDC
  • additionally, brave.baggage.BaggagePropagation is configured to propagate each provided baggage field locally

BraveHelloWorldV1

  • tracer.newTrace() will create a new brave.Span (trace) with a given name
  • Span.tag() is used to set tags on a trace (don't confuse this with baggage though)
  • Span.start() is called to signal that span has started
  • brave.baggage.BaggageField.updateValue() is used to set a baggage value
  • tracer.withSpanInScope(trace) helps with setting the trace as current for a block of code
  • Span.finish() is needed to signal that the span has ended and can be reported to Tempo

BraveExecutorsV1

  • here we create a couple of thread pools / executors for doing processing of each user in 2 stages
  • we use APIs from previous example, but have to run tracer.withSpanInScope(trace) within each task

BraveExecutorsV2

  • this is an improved version of the previous example with executors
  • here each executor is wrapped with tracing.currentTraceContext().executorService()
  • this allows to avoid calling tracer.withSpanInScope() on the nested tasks, as those inherit the trace context
  • underneath, CurrentTraceContextExecutorService is used to capture context of the current trace at the time of calling .submit() on the pool

BraveCoroutinesV1

  • in this version we call tracer.withSpanInScope(trace) outside of coroutine code to make the trace current
  • then we launch a coroutine with kotlinx.coroutines.slf4j.MDCContext added to the context
  • this does not give us trace propagation, but at least MDC values from baggage are maintained between thread switches

BraveCoroutinesV2

  • this example improves the previous one by handling trace propagation within coroutines
  • TracingContextElement is first implemented by extending ThreadContextElement
  • we are then able to add TracingContextElement(tracing.currentTraceContext()) to coroutine context
  • this makes sure that tracing context is restored every time the coroutine switches a thread

BraveReactorV1

  • here we again rely on io.micrometer:context-propagation library
  • ContextRegistry.getInstance().registerThreadLocalAccessor() is used to manipulate tracing.currentTraceContext()