This does two things: ensures samples don't use Zipkin v1 in any way,
and misaligns the version numbers of zipkin v1 and zipkin v2 apis.
This is an attempt to walk around the gradle plugin issue, which only
exists when someone is using both versions of zipkin.
See https://github.com/spring-projects/spring-boot/issues/10778
Also allows us to actually create a PercentageBasedSampler (I
don't think anyone tried it before) without resorting to
lazy beans and proxies.
Another freature added here is a default percentage sampler
if we know that spans need to be exported (zipkin or stream
is present).
Fixes gh-138
- Changed Random instantiation to a shared Random
- Changed the name of the converter
- Changed generator into random
- Span id is now non-nullable.
- it gets generated in the http filter if it's not there
- it's generated in the spring-integration channels if it wasn't set
Recent versions of zipkin and brave operate with http instead of scribe.
This changes the implementation accordingly, as well adds a sampler to
the POST endpoint.
A notable impact is that we no longer require a collector process, as
the zipkin server's POST endpoint is a collector.
Instrumentation should be able to get by with only 2
interfaces: TraceManager and TraceAccessor (the former is
not needed if you aren't starting a new Span). No explicit
access to thread locals or manipulation of thread context
is required (except locally where necessary).
A Span is enclosed by a Trace (actually a view of the complete
Trace that would be constructed remotely).
