brave-context-slf4j

This adds trace and span IDs to the SLF4J Mapped Diagnostic Context (MDC) so that you can search or aggregate logs accordingly.

To enable this, configure brave.Tracing with MDCScopeDecorator like so:

correlationContext = new SLF4JContext();
tracing = Tracing.newBuilder()
    .currentTraceContext(ThreadLocalCurrentTraceContext.newBuilder()
        .addScopeDecorator(MDCScopeDecorator.get()
        .build()
    )
    ...
    .build();

Then, in your log configuration, you can use traceId, parentId, spanId and sampled.

Here's an example logback configuration:

<pattern>%d [%X{traceId}/%X{spanId}] [%thread] %-5level %logger{36} - %msg%n</pattern>

When a trace is in progress, it would log statements like this:

2017-05-02 23:36:04,789 [fcd015bf6f8b05ba/fcd015bf6f8b05ba] [main] INFO  c.a.FooController - I got here!

Users could then copy/paste the trace ID into the zipkin UI, or use log correlation to further debug a problem.