Conditionally initialize the global opentracing tracer

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.

1 files changed, 6 insertions, 0 deletions

diff --git a/Gemfile b/Gemfile
index 515b42dc384..9ef4b791375 100644
--- a/Gemfile
+++ b/Gemfile
@@ -304,6 +304,12 @@ group :metrics do
   gem 'raindrops', '~> 0.18'
 end
 
+group :tracing do
+  # OpenTracing
+  gem 'opentracing', '~> 0.4.3'
+  gem 'jaeger-client', '~> 0.10.0'
+end
+
 group :development do
   gem 'foreman', '~> 0.84.0'
   gem 'brakeman', '~> 4.2', require: false