Add prometheus_endpoint_path for variables

- The metric_label_values type of variable needs the results of a
Prometheus query.

- Similar to how we add a prometheus_endpoint_path key for panels in the
dashboard, add it for variables of type metric_label_values.

app/services/metrics/dashboard/base_service.rb

@@ -10,7 +10,8 @@ module Metrics
       STAGES = ::Gitlab::Metrics::Dashboard::Stages
       SEQUENCE = [
         STAGES::CommonMetricsInserter,
-        STAGES::EndpointInserter,
+        STAGES::MetricEndpointInserter,
+        STAGES::VariableEndpointInserter,
         STAGES::PanelIdsInserter,
         STAGES::Sorter,
         STAGES::AlertsInserter,

app/services/metrics/dashboard/gitlab_alert_embed_service.rb

@@ -11,7 +11,7 @@ module Metrics
       include Gitlab::Utils::StrongMemoize
 
       SEQUENCE = [
-        STAGES::EndpointInserter,
+        STAGES::MetricEndpointInserter,
         STAGES::PanelIdsInserter
       ].freeze
 

app/services/metrics/dashboard/predefined_dashboard_service.rb

@@ -10,7 +10,8 @@ module Metrics
       DASHBOARD_NAME = nil
 
       SEQUENCE = [
-        STAGES::EndpointInserter,
+        STAGES::MetricEndpointInserter,
+        STAGES::VariableEndpointInserter,
         STAGES::PanelIdsInserter,
         STAGES::Sorter
       ].freeze

app/services/metrics/dashboard/self_monitoring_dashboard_service.rb

@@ -10,7 +10,8 @@ module Metrics
 
       SEQUENCE = [
         STAGES::CustomMetricsInserter,
-        STAGES::EndpointInserter,
+        STAGES::MetricEndpointInserter,
+        STAGES::VariableEndpointInserter,
         STAGES::PanelIdsInserter,
         STAGES::Sorter
       ].freeze

app/services/metrics/dashboard/system_dashboard_service.rb

@@ -12,7 +12,8 @@ module Metrics
         STAGES::CommonMetricsInserter,
         STAGES::CustomMetricsInserter,
         STAGES::CustomMetricsDetailsInserter,
-        STAGES::EndpointInserter,
+        STAGES::MetricEndpointInserter,
+        STAGES::VariableEndpointInserter,
         STAGES::PanelIdsInserter,
         STAGES::Sorter,
         STAGES::AlertsInserter

app/services/metrics/dashboard/transient_embed_service.rb

@@ -30,7 +30,7 @@ module Metrics
 
       override :sequence
       def sequence
-        [STAGES::EndpointInserter]
+        [STAGES::MetricEndpointInserter]
       end
 
       override :identifiers

app/services/prometheus/proxy_service.rb

@@ -22,16 +22,20 @@ module Prometheus
 
     attr_accessor :proxyable, :method, :path, :params
 
+    PROMETHEUS_QUERY_API = 'query'
+    PROMETHEUS_QUERY_RANGE_API = 'query_range'
+    PROMETHEUS_SERIES_API = 'series'
+
     PROXY_SUPPORT = {
-      'query' => {
+      PROMETHEUS_QUERY_API => {
         method: ['GET'],
         params: %w(query time timeout)
       },
-      'query_range' => {
+      PROMETHEUS_QUERY_RANGE_API => {
         method: ['GET'],
         params: %w(query start end step timeout)
       },
-      'series' => {
+      PROMETHEUS_SERIES_API => {
         method: %w(GET),
         params: %w(match start end)
       }

lib/gitlab/metrics/dashboard/stages/base_stage.rb

@@ -48,6 +48,14 @@ module Gitlab
             end
           end
 
+          def for_variables
+            return unless dashboard.dig(:templating, :variables).is_a?(Hash)
+
+            dashboard.dig(:templating, :variables).each do |variable_name, variable|
+              yield variable_name, variable
+            end
+          end
+
           def for_panel_groups
             dashboard[:panel_groups].each do |panel_group|
               yield panel_group

lib/gitlab/metrics/dashboard/stages/endpoint_inserter.rb → lib/gitlab/metrics/dashboard/stages/metric_endpoint_inserter.rb

@@ -4,9 +4,9 @@ module Gitlab
   module Metrics
     module Dashboard
       module Stages
-        class EndpointInserter < BaseStage
+        class MetricEndpointInserter < BaseStage
           def transform!
-            raise Errors::DashboardProcessingError.new('Environment is required for Stages::EndpointInserter') unless params[:environment]
+            raise Errors::DashboardProcessingError.new('Environment is required for Stages::MetricEndpointInserter') unless params[:environment]
 
             for_metrics do |metric|
               metric[:prometheus_endpoint_path] = endpoint_for_metric(metric)

lib/gitlab/metrics/dashboard/stages/variable_endpoint_inserter.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Metrics
+    module Dashboard
+      module Stages
+        class VariableEndpointInserter < BaseStage
+          VARIABLE_TYPE_METRIC_LABEL_VALUES = 'metric_label_values'
+
+          def transform!
+            raise Errors::DashboardProcessingError.new(_('Environment is required for Stages::VariableEndpointInserter')) unless params[:environment]
+
+            for_variables do |variable_name, variable|
+              if variable.is_a?(Hash) && variable[:type] == VARIABLE_TYPE_METRIC_LABEL_VALUES
+                variable[:options][:prometheus_endpoint_path] = endpoint_for_variable(variable.dig(:options, :series_selector))
+              end
+            end
+          end
+
+          private
+
+          def endpoint_for_variable(series_selector)
+            Gitlab::Routing.url_helpers.prometheus_api_project_environment_path(
+              project,
+              params[:environment],
+              proxy_path: ::Prometheus::ProxyService::PROMETHEUS_SERIES_API,
+              match: Array(series_selector)
+            )
+          end
+        end
+      end
+    end
+  end
+end

locale/gitlab.pot

@@ -8555,6 +8555,9 @@ msgstr ""
 msgid "Environment does not have deployments"
 msgstr ""
 
+msgid "Environment is required for Stages::VariableEndpointInserter"
+msgstr ""
+
 msgid "Environment scope"
 msgstr ""
 

spec/fixtures/lib/gitlab/metrics/dashboard/sample_dashboard.yml

@@ -24,6 +24,12 @@ templating:
         - value: 'value_option_2'
           text: 'Option 2'
           default: true
+    metric_label_values_variable:
+      label: 'Variable 3'
+      type: metric_label_values
+      options:
+        series_selector: 'backend:haproxy_backend_availability:ratio{env="{{env}}"}'
+        label: 'backend'
 panel_groups:
 - group: Group A
   priority: 1

spec/fixtures/lib/gitlab/metrics/dashboard/schemas/metric_label_values_variable_full_syntax.json

+{
+  "type": "object",
+  "required": [
+    "type", "options"
+  ],
+  "properties": {
+    "type": { "enum": "metric_label_values" },
+    "label": { "type": "string" },
+    "options": { "$ref": "metric_label_values_variable_options.json" }
+  },
+  "additionalProperties": false
+}

spec/fixtures/lib/gitlab/metrics/dashboard/schemas/metric_label_values_variable_options.json

+{
+  "type": "object",
+  "required": [
+    "series_selector", "label", "prometheus_endpoint_path"
+  ],
+  "properties": {
+    "series_selector": { "type": "string" },
+    "label": { "type": "string" },
+    "prometheus_endpoint_path": { "type": "string" }
+  },
+  "additionalProperties": false
+}

spec/fixtures/lib/gitlab/metrics/dashboard/schemas/variables.json

@@ -9,7 +9,8 @@
             "type": "array",
             "items": { "type": "string" }
           },
-          { "$ref": "custom_variable_full_syntax.json" }
+          { "$ref": "custom_variable_full_syntax.json" },
+          { "$ref": "metric_label_values_variable_full_syntax.json" }
         ]
       }
   },

spec/lib/gitlab/metrics/dashboard/processor_spec.rb

@@ -13,7 +13,7 @@ describe Gitlab::Metrics::Dashboard::Processor do
         Gitlab::Metrics::Dashboard::Stages::CommonMetricsInserter,
         Gitlab::Metrics::Dashboard::Stages::CustomMetricsInserter,
         Gitlab::Metrics::Dashboard::Stages::CustomMetricsDetailsInserter,
-        Gitlab::Metrics::Dashboard::Stages::EndpointInserter,
+        Gitlab::Metrics::Dashboard::Stages::MetricEndpointInserter,
         Gitlab::Metrics::Dashboard::Stages::Sorter,
         Gitlab::Metrics::Dashboard::Stages::AlertsInserter,
         Gitlab::Metrics::Dashboard::Stages::PanelIdsInserter,
@@ -98,7 +98,7 @@ describe Gitlab::Metrics::Dashboard::Processor do
         let(:sequence) do
           [
             Gitlab::Metrics::Dashboard::Stages::CommonMetricsInserter,
-            Gitlab::Metrics::Dashboard::Stages::EndpointInserter,
+            Gitlab::Metrics::Dashboard::Stages::MetricEndpointInserter,
             Gitlab::Metrics::Dashboard::Stages::Sorter
           ]
         end

spec/lib/gitlab/metrics/dashboard/stages/variable_endpoint_inserter_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::Metrics::Dashboard::Stages::VariableEndpointInserter do
+  include MetricsDashboardHelpers
+
+  let(:project) { build_stubbed(:project) }
+  let(:environment) { build_stubbed(:environment, project: project) }
+
+  describe '#transform!' do
+    subject(:transform!) { described_class.new(project, dashboard, environment: environment).transform! }
+
+    let(:dashboard) { load_sample_dashboard.deep_symbolize_keys }
+
+    context 'when dashboard variables are present' do
+      it 'assigns prometheus_endpoint_path to metric_label_values variable type' do
+        endpoint_path = Gitlab::Routing.url_helpers.prometheus_api_project_environment_path(
+          project,
+          environment,
+          proxy_path: :series,
+          match: ['backend:haproxy_backend_availability:ratio{env="{{env}}"}']
+        )
+
+        transform!
+
+        expect(
+          dashboard.dig(:templating, :variables, :metric_label_values_variable, :options)
+        ).to include(prometheus_endpoint_path: endpoint_path)
+      end
+
+      it 'does not modify other variable types' do
+        original_text_variable = dashboard[:templating][:variables][:text_variable_full_syntax].deep_dup
+
+        transform!
+
+        expect(dashboard[:templating][:variables][:text_variable_full_syntax]).to eq(original_text_variable)
+      end
+
+      context 'when variable does not have the required series_selector' do
+        it 'adds prometheus_endpoint_path without match parameter' do
+          dashboard[:templating][:variables][:metric_label_values_variable][:options].delete(:series_selector)
+          endpoint_path = Gitlab::Routing.url_helpers.prometheus_api_project_environment_path(
+            project,
+            environment,
+            proxy_path: :series
+          )
+
+          transform!
+
+          expect(
+            dashboard.dig(:templating, :variables, :metric_label_values_variable, :options)
+          ).to include(prometheus_endpoint_path: endpoint_path)
+        end
+      end
+    end
+
+    context 'when no variables are present' do
+      it 'does not fail' do
+        dashboard.delete(:templating)
+
+        expect { transform! }.not_to raise_error
+      end
+    end
+
+    context 'with no environment' do
+      subject(:transform!) { described_class.new(project, dashboard, {}).transform! }
+
+      it 'raises error' do
+        expect { transform! }.to raise_error(
+          Gitlab::Metrics::Dashboard::Errors::DashboardProcessingError,
+          'Environment is required for Stages::VariableEndpointInserter'
+        )
+      end
+    end
+  end
+end

spec/support/helpers/metrics_dashboard_helpers.rb

@@ -18,6 +18,10 @@ module MetricsDashboardHelpers
     project.repository.refresh_method_caches([:metrics_dashboard])
   end
 
+  def load_sample_dashboard
+    YAML.safe_load(fixture_file('lib/gitlab/metrics/dashboard/sample_dashboard.yml'))
+  end
+
   def system_dashboard_path
     Metrics::Dashboard::SystemDashboardService::DASHBOARD_PATH
   end