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.

2 files changed, 88 insertions, 0 deletions

diff --git a/spec/lib/gitlab/tracing/factory_spec.rb b/spec/lib/gitlab/tracing/factory_spec.rb
new file mode 100644
index 00000000000..945490f0988
--- /dev/null
+++ b/spec/lib/gitlab/tracing/factory_spec.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+require 'fast_spec_helper'
+
+describe Gitlab::Tracing::Factory do
+  describe '.create_tracer' do
+    let(:service_name) { 'rspec' }
+
+    context "when tracing is not configured" do
+      it 'ignores null connection strings' do
+        expect(described_class.create_tracer(service_name, nil)).to be_nil
+      end
+
+      it 'ignores empty connection strings' do
+        expect(described_class.create_tracer(service_name, '')).to be_nil
+      end
+
+      it 'ignores unknown implementations' do
+        expect(described_class.create_tracer(service_name, 'opentracing://invalid_driver')).to be_nil
+      end
+
+      it 'ignores invalid connection strings' do
+        expect(described_class.create_tracer(service_name, 'open?tracing')).to be_nil
+      end
+    end
+
+    context "when tracing is configured with jaeger" do
+      let(:mock_tracer) { double('tracer') }
+
+      it 'processes default connections' do
+        expect(Gitlab::Tracing::JaegerFactory).to receive(:create_tracer).with(service_name, {}).and_return(mock_tracer)
+
+        expect(described_class.create_tracer(service_name, 'opentracing://jaeger')).to be(mock_tracer)
+      end
+
+      it 'processes connections with parameters' do
+        expect(Gitlab::Tracing::JaegerFactory).to receive(:create_tracer).with(service_name, { a: '1', b: '2', c: '3' }).and_return(mock_tracer)
+
+        expect(described_class.create_tracer(service_name, 'opentracing://jaeger?a=1&b=2&c=3')).to be(mock_tracer)
+      end
+    end
+  end
+end
diff --git a/spec/lib/gitlab/tracing/jaeger_factory_spec.rb b/spec/lib/gitlab/tracing/jaeger_factory_spec.rb
new file mode 100644
index 00000000000..3bffeb28830
--- /dev/null
+++ b/spec/lib/gitlab/tracing/jaeger_factory_spec.rb
@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+require 'fast_spec_helper'
+
+describe Gitlab::Tracing::JaegerFactory do
+  describe '.create_tracer' do
+    let(:service_name) { 'rspec' }
+
+    it 'processes default connections' do
+      expect(described_class.create_tracer(service_name, {})).to respond_to(:active_span)
+    end
+
+    it 'handles debug options' do
+      expect(described_class.create_tracer(service_name, { debug: "1" })).to respond_to(:active_span)
+    end
+
+    it 'handles const sampler' do
+      expect(described_class.create_tracer(service_name, { sampler: "const", sampler_param: "1" })).to respond_to(:active_span)
+    end
+
+    it 'handles probabilistic sampler' do
+      expect(described_class.create_tracer(service_name, { sampler: "probabilistic", sampler_param: "0.5" })).to respond_to(:active_span)
+    end
+
+    it 'handles http_endpoint configurations' do
+      expect(described_class.create_tracer(service_name, { http_endpoint: "http://localhost:1234" })).to respond_to(:active_span)
+    end
+
+    it 'handles udp_endpoint configurations' do
+      expect(described_class.create_tracer(service_name, { udp_endpoint: "localhost:4321" })).to respond_to(:active_span)
+    end
+
+    it 'ignores invalid parameters' do
+      expect(described_class.create_tracer(service_name, { invalid: "true" })).to respond_to(:active_span)
+    end
+
+    it 'accepts the debug parameter when strict_parser is set' do
+      expect(described_class.create_tracer(service_name, { debug: "1", strict_parsing: "1" })).to respond_to(:active_span)
+    end
+
+    it 'rejects invalid parameters when strict_parser is set' do
+      expect { described_class.create_tracer(service_name, { invalid: "true", strict_parsing: "1" }) }.to raise_error(StandardError)
+    end
+  end
+end