Handle unknown dashboard attributes

PanelIdInserter stage in dashbaord processing should be prepared to
greacefully handle unknown, wrong dashboard panle attributes,
with out breaking whole breaking whole dashboard. In order to that
we are going to rescue error and silently pass them back to Sentry,
while skipping PanelIdInserter stage for malformed dashboard.

app/models/performance_monitoring/prometheus_panel.rb

@@ -4,7 +4,7 @@ module PerformanceMonitoring
   class PrometheusPanel
     include ActiveModel::Model
 
-    attr_accessor :type, :title, :y_label, :weight, :metrics, :y_axis
+    attr_accessor :type, :title, :y_label, :weight, :metrics, :y_axis, :max_value
 
     validates :title, presence: true
     validates :metrics, presence: true

changelogs/unreleased/214360-custom-metrics-dashboard-does-not-load-when-max_value-is-set.yml

+---
+title: Fix dashboard processing error which prevented dashboards with unknown attributes
+  inside panels from being displayed
+merge_request: 29517
+author:
+type: fixed

ee/spec/models/performance_monitoring/prometheus_panel_spec.rb

@@ -5,6 +5,7 @@ require 'spec_helper'
 describe PerformanceMonitoring::PrometheusPanel do
   let(:json_content) do
     {
+      "max_value" => 1,
       "type" => "area-chart",
       "title" => "Chart Title",
       "y_label" => "Y-Axis",

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

@@ -15,6 +15,9 @@ module Gitlab
 
               insert_panel_id(id, panel)
             end
+          rescue ActiveModel::UnknownAttributeError => error
+            remove_panel_ids!
+            Gitlab::ErrorTracking.log_exception(error)
           end
 
           private

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

@@ -8,6 +8,7 @@ panel_groups:
     type: "area-chart"
     y_label: "y_label"
     weight: 1
+    max_value: 1
     metrics:
     - id: metric_a1
       query_range: 'query'

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

@@ -11,6 +11,7 @@
     "type": { "type": "string" },
     "y_label": { "type": "string" },
     "y_axis": { "$ref": "axis.json" },
+    "max_value": { "type": "number" },
     "weight": { "type": "number" },
     "metrics": {
       "type": "array",

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

@@ -15,7 +15,8 @@ describe Gitlab::Metrics::Dashboard::Processor do
         Gitlab::Metrics::Dashboard::Stages::CustomMetricsDetailsInserter,
         Gitlab::Metrics::Dashboard::Stages::EndpointInserter,
         Gitlab::Metrics::Dashboard::Stages::Sorter,
-        Gitlab::Metrics::Dashboard::Stages::AlertsInserter
+        Gitlab::Metrics::Dashboard::Stages::AlertsInserter,
+        Gitlab::Metrics::Dashboard::Stages::PanelIdsInserter
       ]
     end
 
@@ -28,6 +29,12 @@ describe Gitlab::Metrics::Dashboard::Processor do
       end
     end
 
+    it 'includes an id for each dashboard panel' do
+      expect(all_panels).to satisfy_all do |panel|
+        panel[:id].present?
+      end
+    end
+
     it 'includes boolean to indicate if panel group has custom metrics' do
       expect(dashboard[:panel_groups]).to all(include( { has_custom_metrics: boolean } ))
     end
@@ -199,9 +206,11 @@ describe Gitlab::Metrics::Dashboard::Processor do
   private
 
   def all_metrics
-    dashboard[:panel_groups].flat_map do |group|
-      group[:panels].flat_map { |panel| panel[:metrics] }
+    all_panels.flat_map { |panel| panel[:metrics] }
   end
+
+  def all_panels
+    dashboard[:panel_groups].flat_map { |group| group[:panels] }
   end
 
   def get_metric_details(metric)

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

@@ -63,5 +63,24 @@ describe Gitlab::Metrics::Dashboard::Stages::PanelIdsInserter do
         )
       end
     end
+
+    context 'when dashboard panels has unknown schema attributes' do
+      before do
+        error = ActiveModel::UnknownAttributeError.new(double, 'unknown_panel_attribute')
+        allow(::PerformanceMonitoring::PrometheusPanel).to receive(:new).and_raise(error)
+      end
+
+      it 'no panel has assigned id' do
+        transform!
+
+        expect(fetch_panel_ids(dashboard)).to all be_nil
+      end
+
+      it 'logs the failure' do
+        expect(Gitlab::ErrorTracking).to receive(:log_exception)
+
+        transform!
+      end
+    end
   end
 end