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, 13 insertions, 0 deletions

diff --git a/config/initializers/tracing.rb b/config/initializers/tracing.rb
new file mode 100644
index 00000000000..be95f30d075
--- /dev/null
+++ b/config/initializers/tracing.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+if Gitlab::Tracing.enabled?
+  require 'opentracing'
+
+  # In multi-processed clustered architectures (puma, unicorn) don't
+  # start tracing until the worker processes are spawned. This works
+  # around issues when the opentracing implementation spawns threads
+  Gitlab::Cluster::LifecycleEvents.on_worker_start do
+    tracer = Gitlab::Tracing::Factory.create_tracer(Gitlab.process_name, Gitlab::Tracing.connection_string)
+    OpenTracing.global_tracer = tracer if tracer
+  end
+end