During the review process for adding opentracing factories, a bug was
introduced which caused Jaeger to initialize an invalid tracer. The
bug was due to use sending nil through as a kwarg when the Jaeger
initializer used a non-nil default value.
This is fairly insidious as, the tracer looks like a tracer, but, when
methods are invoked, it throws `NoMethodError` errors. To ensure that
this issue does not happen in future, the tests have been changed to
ensure that the tracer works as expected. This could avoid problems
in future when upgrading to newer versions of Jaeger.
This change will instantiate an OpenTracing tracer and configure it
as the global tracer when the GITLAB_TRACING environment variable is
configured. GITLAB_TRACING takes a "connection string"-like value,
encapsulating the driver (eg jaeger, etc) and options for the driver.
Since each service, whether it's written in Ruby or Golang, uses the
same connection-string, it should be very easy to configure all
services in a cluster, or even a single development machine to be
setup to use tracing.
Note that this change does not include instrumentation or propagation
changes as this is a way of breaking a previous larger change into
components. The instrumentation and propagation changes will follow
in separate changes.
