Add opentracing integration for graphql

Extends existing graphql's tracer with opentracing measurements. Because
it also adds Tracing::Graphql class (for opentracing), it also renames
Graphql::Tracing class to Graphql::GenericTracing to minimize confusion
with similar class names.

Gemfile

@@ -276,7 +276,7 @@ gem 'sentry-raven', '~> 2.7'
 gem 'premailer-rails', '~> 1.9.7'
 
 # LabKit: Tracing and Correlation
-gem 'gitlab-labkit', '~> 0.1.2'
+gem 'gitlab-labkit', '~> 0.2.0'
 
 # I18n
 gem 'ruby_parser', '~> 3.8', require: false

Gemfile.lock

@@ -288,7 +288,7 @@ GEM
     github-markup (1.7.0)
     gitlab-default_value_for (3.1.1)
       activerecord (>= 3.2.0, < 6.0)
-    gitlab-labkit (0.1.2)
+    gitlab-labkit (0.2.0)
       actionpack (~> 5)
       activesupport (~> 5)
       grpc (~> 1.15)
@@ -1059,7 +1059,7 @@ DEPENDENCIES
   gitaly-proto (~> 1.26.0)
   github-markup (~> 1.7.0)
   gitlab-default_value_for (~> 3.1.1)
-  gitlab-labkit (~> 0.1.2)
+  gitlab-labkit (~> 0.2.0)
   gitlab-markup (~> 1.7.0)
   gitlab-sidekiq-fetcher (~> 0.4.0)
   gitlab-styles (~> 2.5)

app/graphql/gitlab_schema.rb

@@ -11,7 +11,7 @@ class GitlabSchema < GraphQL::Schema
   use Gitlab::Graphql::Authorize
   use Gitlab::Graphql::Present
   use Gitlab::Graphql::Connections
-  use Gitlab::Graphql::Tracing
+  use Gitlab::Graphql::GenericTracing
 
   query_analyzer Gitlab::Graphql::QueryAnalyzers::LogQueryComplexity.analyzer
 

lib/gitlab/graphql/tracing.rb → lib/gitlab/graphql/generic_tracing.rb

 # frozen_string_literal: true
 
+# This class is used as a hook to observe graphql runtime events. From this
+# hook both gitlab metrics and opentracking measurements are generated
+
 module Gitlab
   module Graphql
-    class Tracing < GraphQL::Tracing::PlatformTracing
+    class GenericTracing < GraphQL::Tracing::PlatformTracing
       self.platform_keys = {
         'lex' => 'graphql.lex',
         'parse' => 'graphql.parse',
@@ -21,17 +24,30 @@ module Gitlab
       end
 
       def platform_trace(platform_key, key, data, &block)
+        tags = { platform_key: platform_key, key: key }
         start = Gitlab::Metrics::System.monotonic_time
 
-        yield
+        with_labkit_tracing(tags, &block)
       ensure
         duration = Gitlab::Metrics::System.monotonic_time - start
 
-        graphql_duration_seconds.observe({ platform_key: platform_key, key: key }, duration)
+        graphql_duration_seconds.observe(tags, duration)
       end
 
       private
 
+      def with_labkit_tracing(tags, &block)
+        return yield unless Labkit::Tracing.enabled?
+
+        name = "#{tags[:platform_key]}.#{tags[:key]}"
+        span_tags = {
+          'component' => 'web',
+          'span.kind' => 'server'
+        }.merge(tags.stringify_keys)
+
+        Labkit::Tracing.with_tracing(operation_name: name, tags: span_tags, &block)
+      end
+
       def graphql_duration_seconds
         @graphql_duration_seconds ||= Gitlab::Metrics.histogram(
           :graphql_duration_seconds,

spec/lib/gitlab/graphql/tracing_spec.rb → spec/lib/gitlab/graphql/generic_tracing_spec.rb

@@ -2,7 +2,7 @@
 
 require 'spec_helper'
 
-describe Gitlab::Graphql::Tracing do
+describe Gitlab::Graphql::GenericTracing do
   let(:graphql_duration_seconds_histogram) { double('Gitlab::Metrics::NullMetric') }
 
   it 'updates graphql histogram with expected labels' do
@@ -23,6 +23,40 @@ describe Gitlab::Graphql::Tracing do
     GitlabSchema.execute(query, context: { tracers: [tracer] })
   end
 
+  context "when labkit tracing is enabled" do
+    before do
+      expect(Labkit::Tracing).to receive(:enabled?).and_return(true)
+    end
+
+    it 'yields with labkit tracing' do
+      expected_tags = {
+        'component' => 'web',
+        'span.kind' => 'server',
+        'platform_key' => 'pkey',
+        'key' => 'key'
+      }
+
+      expect(Labkit::Tracing)
+        .to receive(:with_tracing)
+        .with(operation_name: "pkey.key", tags: expected_tags)
+        .and_yield
+
+      expect { |b| described_class.new.platform_trace('pkey', 'key', nil, &b) }.to yield_control
+    end
+  end
+
+  context "when labkit tracing is disabled" do
+    before do
+      expect(Labkit::Tracing).to receive(:enabled?).and_return(false)
+    end
+
+    it 'yields without measurement' do
+      expect(Labkit::Tracing).not_to receive(:with_tracing)
+
+      expect { |b| described_class.new.platform_trace('pkey', 'key', nil, &b) }.to yield_control
+    end
+  end
+
   private
 
   def expect_metric(platform_key, key)