[+] mongo service name resolver for multi cluster mongo (#1423)

Co-authored-by: Marco Costa <marco.costa@datadoghq.com>

docs/GettingStarted.md

@@ -1222,6 +1222,37 @@ Where `options` is an optional `Hash` that accepts the following parameters:
 | `quantize` | Hash containing options for quantization. May include `:show` with an Array of keys to not quantize (or `:all` to skip quantization), or `:exclude` with Array of keys to exclude entirely. | `{ show: [:collection, :database, :operation] }` |
 | `service_name` | Service name used for `mongo` instrumentation | `'mongodb'` |
 
+**Configuring trace settings per connection**
+
+You can configure trace settings per connection by using the `describes` option:
+
+```ruby
+# Provide a `:describes` option with a connection key.
+# Any of the following keys are acceptable and equivalent to one another.
+# If a block is provided, it yields a Settings object that
+# accepts any of the configuration options listed above.
+
+Datadog.configure do |c|
+  # Network connection string
+  c.use :mongo, describes: '127.0.0.1:27017', service_name: 'mongo-primary'
+
+  # Network connection regular expression
+  c.use :mongo, describes: /localhost.*/, service_name: 'mongo-secondary'
+end
+
+client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'artists')
+collection = client[:people]
+collection.insert_one({ name: 'Steve' })
+# Traced call will belong to `mongo-primary` service
+
+client = Mongo::Client.new([ 'localhost:27017' ], :database => 'artists')
+collection = client[:people]
+collection.insert_one({ name: 'Steve' })
+# Traced call will belong to `mongo-secondary` service
+```
+
+When multiple `describes` configurations match a connection, the latest configured rule that matches will be applied.
+
 ### MySQL2
 
 The MySQL2 integration traces any SQL command sent through `mysql2` gem.

lib/ddtrace/contrib/mongodb/instrumentation.rb

@@ -52,7 +52,7 @@ def self.included(base)
           module InstanceMethods
             def datadog_pin
               @datadog_pin ||= begin
-                service = Datadog.configuration[:mongo][:service_name]
+                service = Datadog.configuration[:mongo, seed][:service_name]
 
                 Datadog::Pin.new(
                   service,

lib/ddtrace/contrib/mongodb/integration.rb

@@ -1,5 +1,6 @@
 # typed: false
 require 'ddtrace/contrib/integration'
+require 'ddtrace/contrib/configuration/resolvers/pattern_resolver'
 require 'ddtrace/contrib/mongodb/configuration/settings'
 require 'ddtrace/contrib/mongodb/patcher'
 
@@ -33,6 +34,10 @@ def default_configuration
         def patcher
           Patcher
         end
+
+        def resolver
+          @resolver ||= Contrib::Configuration::Resolvers::PatternResolver.new
+        end
       end
     end
   end

spec/ddtrace/contrib/mongodb/client_spec.rb

@@ -65,6 +65,60 @@
       it_behaves_like 'a peer service span'
     end
 
+    context 'with a different service name using describes option' do
+      let(:primary_service) { 'mongodb-primary' }
+      let(:secondary_service) { 'mongodb-secondary' }
+      let(:secondary_client) { Mongo::Client.new(["#{secondary_host}:#{port}"], client_options) }
+      let(:secondary_host) { 'localhost' }
+
+      before do
+        Datadog.configure do |c|
+          c.use :mongo, describes: /#{host}/ do |mongo|
+            mongo.service_name = primary_service
+          end
+
+          c.use :mongo, describes: /#{secondary_host}/ do |mongo|
+            mongo.service_name = secondary_service
+          end
+        end
+      end
+
+      context 'primary client' do
+        subject { client[collection].insert_one(name: 'FKA Twigs') }
+
+        it 'produces spans with the correct service' do
+          subject
+          expect(spans).to have(1).items
+          expect(spans.first.service).to eq(primary_service)
+        end
+
+        it_behaves_like 'a peer service span'
+      end
+
+      context 'secondary client' do
+        around do |example|
+          without_warnings do
+            # Reset before and after each example; don't allow global state to linger.
+            Datadog.registry[:mongo].reset_configuration!
+            example.run
+            Datadog.registry[:mongo].reset_configuration!
+            secondary_client.database.drop if drop_database?
+            secondary_client.close
+          end
+        end
+
+        subject { secondary_client[collection].insert_one(name: 'FKA Twigs') }
+
+        it 'produces spans with the correct service' do
+          subject
+          expect(spans).to have(1).items
+          expect(spans.first.service).to eq(secondary_service)
+        end
+
+        it_behaves_like 'a peer service span'
+      end
+    end
+
     context 'to disable the tracer' do
       before { tracer.enabled = false }