Add service tag to health metrics

lib/datadog/core/configuration/components.rb

@@ -19,11 +19,13 @@ module Configuration
       class Components
         class << self
           def build_health_metrics(settings)
-            settings = settings.diagnostics.health_metrics
-            options = { enabled: settings.enabled }
-            options[:statsd] = settings.statsd unless settings.statsd.nil?
+            health_settings = settings.diagnostics.health_metrics
 
-            Core::Diagnostics::Health::Metrics.new(**options)
+            Core::Diagnostics::Health::Metrics.new(
+              service: settings.service,
+              enabled: health_settings.enabled,
+              statsd: health_settings.statsd
+            )
           end
 
           def build_logger(settings)

lib/datadog/core/diagnostics/health.rb

@@ -1,4 +1,4 @@
-# typed: strict
+# typed: true
 
 require 'datadog/core/diagnostics/ext'
 require 'datadog/core/metrics/client'
@@ -10,6 +10,13 @@ module Diagnostics
       module Health
         # Health metrics for diagnostics
         class Metrics < Core::Metrics::Client
+          def initialize(service:, enabled: true, statsd: nil)
+            super(enabled: enabled, statsd: statsd)
+            @service = service
+
+            @tags = compile_tags!
+          end
+
           count :api_errors, Ext::Health::Metrics::METRIC_API_ERRORS
           count :api_requests, Ext::Health::Metrics::METRIC_API_REQUESTS
           count :api_responses, Ext::Health::Metrics::METRIC_API_RESPONSES
@@ -30,6 +37,26 @@ class Metrics < Core::Metrics::Client
           gauge :queue_max_length, Ext::Health::Metrics::METRIC_QUEUE_MAX_LENGTH
           gauge :queue_spans, Ext::Health::Metrics::METRIC_QUEUE_SPANS
           gauge :sampling_service_cache_length, Ext::Health::Metrics::METRIC_SAMPLING_SERVICE_CACHE_LENGTH
+
+          def default_metric_options
+            return super unless @tags
+
+            # Return dupes, so that the constant isn't modified,
+            # and defaults are unfrozen for mutation in Statsd.
+            super.tap do |options|
+              options[:tags] = options[:tags].dup
+              options[:tags] << @tags
+            end
+          end
+
+          private
+
+          # Cache tag strings to avoid recreating them on every flush operation.
+          def compile_tags!
+            return unless @service
+
+            "#{Environment::Ext::TAG_SERVICE}:#{@service}".freeze
+          end
         end
       end
     end

spec/datadog/core/configuration/components_spec.rb

@@ -95,7 +95,13 @@
     context 'given settings' do
       shared_examples_for 'new health metrics' do
         let(:health_metrics) { instance_double(Datadog::Core::Diagnostics::Health::Metrics) }
-        let(:default_options) { { enabled: settings.diagnostics.health_metrics.enabled } }
+        let(:default_options) do
+          {
+            service: settings.service,
+            enabled: settings.diagnostics.health_metrics.enabled,
+            statsd: settings.diagnostics.health_metrics.statsd,
+          }
+        end
         let(:options) { {} }
 
         before do
@@ -138,6 +144,18 @@
           let(:options) { { statsd: statsd } }
         end
       end
+
+      context 'with :service' do
+        let(:service) { double('service') }
+
+        before do
+          allow(settings).to receive(:service).and_return(service)
+        end
+
+        it_behaves_like 'new health metrics' do
+          let(:options) { { service: service } }
+        end
+      end
     end
   end
 

spec/datadog/core/diagnostics/health_spec.rb

@@ -3,9 +3,12 @@
 require 'spec_helper'
 require 'ddtrace'
 require 'datadog/core/diagnostics/health'
+require 'datadog/statsd'
 
 RSpec.describe Datadog::Core::Diagnostics::Health::Metrics do
-  subject(:health_metrics) { described_class.new }
+  subject(:health_metrics) { described_class.new(service: service, statsd: statsd) }
+  let(:service) { nil }
+  let(:statsd) { instance_double(Datadog::Statsd) }
 
   shared_examples_for 'a health metric' do |type, name, stat|
     subject(:health_metric) { health_metrics.send(name, *args, &block) }
@@ -43,4 +46,24 @@
   it_behaves_like 'a health metric', :gauge, :queue_spans, Datadog::Core::Diagnostics::Ext::Health::Metrics::METRIC_QUEUE_SPANS
   it_behaves_like 'a health metric', :gauge, :sampling_service_cache_length, Datadog::Core::Diagnostics::Ext::Health::Metrics::METRIC_SAMPLING_SERVICE_CACHE_LENGTH
   # rubocop:enable Layout/LineLength
+
+  describe '.new' do
+    context 'with service' do
+      let(:service) { 'srv' }
+
+      it 'sets the statsd service tag' do
+        expect(statsd).to receive(:count).with(any_args, tags: array_including('service:srv'))
+        health_metrics.api_requests(1)
+      end
+    end
+
+    context 'with no service' do
+      let(:service) { nil }
+
+      it 'does not set the statsd service tag' do
+        expect(statsd).to_not receive(:count).with(any_args, tags: array_including(include('service:')))
+        health_metrics.api_requests(1)
+      end
+    end
+  end
 end