Merge branch 'jprovazn-graphql-prometheus' into 'master'

Monitor GraphQL with Prometheus (try 2)

See merge request gitlab-org/gitlab-ce!26917

app/graphql/gitlab_schema.rb

@@ -5,6 +5,7 @@ class GitlabSchema < GraphQL::Schema
   use Gitlab::Graphql::Authorize
   use Gitlab::Graphql::Present
   use Gitlab::Graphql::Connections
+  use Gitlab::Graphql::Tracing
 
   query(Types::QueryType)
 

changelogs/unreleased/graphql-prometheus.yml

+---
+title: Added prometheus monitoring to GraphQL
+merge_request:
+author:
+type: added

lib/gitlab/graphql/tracing.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Graphql
+    class Tracing < GraphQL::Tracing::PlatformTracing
+      self.platform_keys = {
+        'lex' => 'graphql.lex',
+        'parse' => 'graphql.parse',
+        'validate' => 'graphql.validate',
+        'analyze_query' => 'graphql.analyze',
+        'analyze_multiplex' => 'graphql.analyze',
+        'execute_multiplex' => 'graphql.execute',
+        'execute_query' => 'graphql.execute',
+        'execute_query_lazy' => 'graphql.execute',
+        'execute_field' => 'graphql.execute',
+        'execute_field_lazy' => 'graphql.execute'
+      }
+
+      def platform_field_key(type, field)
+        "#{type.name}.#{field.name}"
+      end
+
+      def platform_trace(platform_key, key, data, &block)
+        start = Gitlab::Metrics::System.monotonic_time
+
+        yield
+      ensure
+        duration = Gitlab::Metrics::System.monotonic_time - start
+
+        graphql_duration_seconds.observe({ platform_key: platform_key, key: key }, duration)
+      end
+
+      private
+
+      def graphql_duration_seconds
+        @graphql_duration_seconds ||= Gitlab::Metrics.histogram(
+          :graphql_duration_seconds,
+          'GraphQL execution time'
+        )
+      end
+    end
+  end
+end

spec/lib/gitlab/graphql/tracing_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::Graphql::Tracing do
+  let(:graphql_duration_seconds_histogram) { double('Gitlab::Metrics::NullMetric') }
+
+  it 'updates graphql histogram with expected labels' do
+    query = 'query { users { id } }'
+    tracer = described_class.new
+
+    allow(tracer)
+      .to receive(:graphql_duration_seconds)
+      .and_return(graphql_duration_seconds_histogram)
+
+    expect_metric('graphql.lex', 'lex')
+    expect_metric('graphql.parse', 'parse')
+    expect_metric('graphql.validate', 'validate')
+    expect_metric('graphql.analyze', 'analyze_multiplex')
+    expect_metric('graphql.execute', 'execute_query_lazy')
+    expect_metric('graphql.execute', 'execute_multiplex')
+
+    GitlabSchema.execute(query, context: { tracers: [tracer] })
+  end
+
+  private
+
+  def expect_metric(platform_key, key)
+    expect(graphql_duration_seconds_histogram)
+      .to receive(:observe)
+      .with({ platform_key: platform_key, key: key }, be > 0.0)
+  end
+end