Monitor GraphQL with Prometheus

Extends graphql's platform tracing class to observe duration
of graphql methods.

In graphql 1.8.11 is added prometheus class but it's not very useful
for us because it uses prometheus_exporter to export results.

1 files changed, 35 insertions, 0 deletions

diff --git a/spec/lib/gitlab/graphql/tracing_spec.rb b/spec/lib/gitlab/graphql/tracing_spec.rb
new file mode 100644
index 00000000000..6bae737d0f6
--- /dev/null
+++ b/spec/lib/gitlab/graphql/tracing_spec.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::Graphql::Tracing do
+  let!(:graphql_duration_seconds) { double('Gitlab::Metrics::NullMetric') }
+
+  before do
+    allow(Gitlab::Metrics)
+      .to receive(:histogram)
+      .with(:graphql_duration_seconds, 'GraphQL execution time')
+      .and_return(graphql_duration_seconds)
+  end
+
+  it 'updates graphql histogram with expected labels' do
+    query = 'query { users { id } }'
+
+    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)
+  end
+
+  private
+
+  def expect_metric(platform_key, key)
+    expect(graphql_duration_seconds)
+      .to receive(:observe)
+      .with({ platform_key: platform_key, key: key }, be > 0.0)
+  end
+end