feat: make the install of rack instrumentation by grape instrumentation optional (#1043)

* feat: optional rack instrumentation install by grape instrumentation

In some circumstances we may want to defer the installation of the rack
instrumentation that is orchestrated during the grape instrumentation
installation. For example, we may want to customise the installation of
the rack instrumentation or we can rely on the installation being
orchestrated by another framework's instrumentation (such as when Grape
is mounted with Rails).

This change allows for Grape to skip the installation of the Rack
instrumentation so that it can manually installed at a later time.

* move the comments above the class name for RubyDocs

Author: chrisholmes

instrumentation/grape/lib/opentelemetry/instrumentation/grape/instrumentation.rb

@@ -8,6 +8,16 @@ module OpenTelemetry
   module Instrumentation
     module Grape
       # The Instrumentation class contains logic to detect and install the Grape instrumentation
+      # # Configuration keys and options
+      # ## `:ignored_events`
+      #
+      # Default is `[]`. Specifies which ActiveSupport::Notifications events published by Grape to ignore.
+      # Ignored events will not be published as Span events.
+      #
+      # ## `:install_rack`
+      #
+      # Default is `true`. Specifies whether or not to install the Rack instrumentation as part of installing the Grape instrumentation.
+      # This is useful in cases where you have multiple Rack applications but want to manually specify where to insert the tracing middleware.
       class Instrumentation < OpenTelemetry::Instrumentation::Base
         # Minimum Grape version needed for compatibility with this instrumentation
         MINIMUM_VERSION = Gem::Version.new('1.2.0')
@@ -27,6 +37,7 @@ class Instrumentation < OpenTelemetry::Instrumentation::Base
         end
 
         option :ignored_events, default: [], validate: :array
+        option :install_rack, default: true, validate: :boolean
 
         private
 
@@ -35,6 +46,8 @@ def gem_version
         end
 
         def install_rack_instrumentation
+          return unless config[:install_rack]
+
           OpenTelemetry::Instrumentation::Rack::Instrumentation.instance.install({})
         end
 

instrumentation/grape/test/opentelemetry/instrumentation/grape_test.rb

@@ -418,5 +418,56 @@ class IgnoredEventAPI < Grape::API
         _(events_per_name('grape.endpoint_render').length).must_equal 0
       end
     end
+
+    describe 'when install_rack is set to false' do
+      class BasicAPI < Grape::API
+        format :json
+        get :hello do
+          { message: 'Hello, world!' }
+        end
+      end
+
+      let(:config) { { install_rack: false } }
+
+      let(:app) do
+        builder = Rack::Builder.app do
+          run BasicAPI
+        end
+        Rack::MockRequest.new(builder)
+      end
+
+      let(:request_path) { '/hello' }
+      let(:expected_span_name) { 'HTTP GET /hello' }
+
+      describe 'missing rack installation' do
+        it 'disables tracing' do
+          app.get request_path
+          _(exporter.finished_spans).must_be_empty
+        end
+      end
+
+      describe 'when rack is manually installed' do
+        let(:app) do
+          build_rack_app(BasicAPI)
+        end
+
+        before do
+          OpenTelemetry::Instrumentation::Rack::Instrumentation.instance.install
+        end
+
+        it 'creates a span' do
+          app.get request_path
+          _(exporter.finished_spans.first.attributes).must_equal(
+            'code.namespace' => 'BasicAPI',
+            'http.method' => 'GET',
+            'http.host' => 'unknown',
+            'http.scheme' => 'http',
+            'http.target' => '/hello',
+            'http.route' => '/hello',
+            'http.status_code' => 200
+          )
+        end
+      end
+    end
   end
 end