add consul failsafes to several request-critical paths

Change-Id: I8d81da166a2d7fb79da1e722135d59b18b6e7825
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/270783
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Jacob Burroughs <jburroughs@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>

app/controllers/application_controller.rb

@@ -2786,7 +2786,7 @@ class ApplicationController < ActionController::Base
       false
     else
       return value_to_boolean(params[:force_stream]) if params.key?(:force_stream)
-      ::Canvas::DynamicSettings.find(tree: :private)["enable_template_streaming"] &&
+      ::Canvas::DynamicSettings.find(tree: :private)["enable_template_streaming", failsafe: false] &&
         Setting.get("disable_template_streaming_for_#{controller_name}/#{action_name}", "false") != "true"
     end
   end

app/helpers/datadog_rum_helper.rb

@@ -67,7 +67,7 @@ module DatadogRumHelper
   end
 
   def sample_rate
-    datadog_rum_config[:sample_rate_percentage].to_f / 100
+    datadog_rum_config[:sample_rate_percentage, failsafe: 0.0].to_f / 100
   end
 
   def datadog_rum_config
@@ -76,7 +76,7 @@ module DatadogRumHelper
 
   def complete_config?
     %i[client_token application_id sample_rate_percentage].all? do |key|
-      datadog_rum_config[key].present?
+      datadog_rum_config[key, failsafe: nil].present?
     end
   end
 end

app/helpers/full_story_helper.rb

@@ -28,13 +28,13 @@ module FullStoryHelper
     return if session.key?(:fullstory_enabled)
 
     fsconfig = Canvas::DynamicSettings.find('fullstory', tree: 'config', service: 'canvas')
-    rate = fsconfig[:sampling_rate].to_f
+    rate = fsconfig[:sampling_rate, failsafe: 0.0].to_f
     sample = rand()
     session[:fullstory_enabled] = rate >= 0.0 && rate <= 1.0 && sample < rate
   end
 
   def fullstory_app_key
-    Canvas::DynamicSettings.find('fullstory', tree: 'config', service: 'canvas')[:app_key] rescue nil
+    Canvas::DynamicSettings.find('fullstory', tree: 'config', service: 'canvas')[:app_key, failsafe: nil]
   end
 
   def fullstory_enabled_for_session?(session)

app/middleware/request_throttle.rb

@@ -195,7 +195,7 @@ class RequestThrottle
   end
 
   def self.dynamic_settings
-    @dynamic_settings ||= YAML.safe_load(Canvas::DynamicSettings.find(tree: :private)['request_throttle.yml'] || '') || {}
+    @dynamic_settings ||= YAML.safe_load(Canvas::DynamicSettings.find(tree: :private)['request_throttle.yml', failsafe: ''] || '') || {}
   end
 
   def rate_limit_exceeded

app/models/user_learning_object_scopes.rb

@@ -282,7 +282,7 @@ module UserLearningObjectScopes
 
   # opts forwaded to course_ids_for_todo_lists
   def submissions_needing_grading_count(**opts)
-    if ::Canvas::DynamicSettings.find(tree: :private, cluster: Shard.current.database_server.id)["disable_needs_grading_queries"]
+    if ::Canvas::DynamicSettings.find(tree: :private, cluster: Shard.current.database_server.id)["disable_needs_grading_queries", failsafe: false]
       return 0
     end
     course_ids = course_ids_for_todo_lists(:manage_grades, **opts)

config/application.rb

@@ -159,10 +159,10 @@ module CanvasRails
 
     config.middleware.use Rack::Chunked
     config.middleware.use Rack::Deflater, if: -> (*) {
-      ::Canvas::DynamicSettings.find(tree: :private)["enable_rack_deflation"]
+      ::Canvas::DynamicSettings.find(tree: :private)["enable_rack_deflation", failsafe: true]
     }
     config.middleware.use Rack::Brotli, if: -> (*) {
-      ::Canvas::DynamicSettings.find(tree: :private)["enable_rack_brotli"]
+      ::Canvas::DynamicSettings.find(tree: :private)["enable_rack_brotli", failsafe: true]
     }
 
     config.i18n.load_path << Rails.root.join('config', 'locales', 'locales.yml')

spec/helpers/datadog_rum_helper_spec.rb

@@ -24,11 +24,11 @@ describe DatadogRumHelper do
   include ApplicationHelper
 
   let(:datadog_rum_config) do
-    {
+    DynamicSettings::FallbackProxy.new(
       application_id: "27627d1e-8a4f-4645-b390-bb396fc83c81",
       client_token: "a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r",
       sample_rate_percentage: 100.0
-    }
+    )
   end
 
   describe "#include_datadog_rum_js?" do
@@ -50,33 +50,33 @@ describe DatadogRumHelper do
       end
 
       it "returns true when the random value is below the sample rate" do
-        datadog_rum_config[:sample_rate_percentage] = 50.0001
+        datadog_rum_config.data[:sample_rate_percentage] = 50.0001
         expect(include_datadog_rum_js?).to be(true)
       end
 
       it "returns true when the random value matches the sample rate" do
-        datadog_rum_config[:sample_rate_percentage] = 50.0
+        datadog_rum_config.data[:sample_rate_percentage] = 50.0
         expect(include_datadog_rum_js?).to be(true)
       end
 
       it "returns false when the random value is above the sample rate" do
-        datadog_rum_config[:sample_rate_percentage] = 49.9999
+        datadog_rum_config.data[:sample_rate_percentage] = 49.9999
         expect(include_datadog_rum_js?).to be(false)
       end
 
       it "returns true when the sample rate percentage is 100%" do
-        datadog_rum_config[:sample_rate_percentage] = 100.0
+        datadog_rum_config.data[:sample_rate_percentage] = 100.0
         expect(include_datadog_rum_js?).to be(true)
       end
 
       it "returns false when the sample rate percentage is 0%" do
         allow(self).to receive(:random).and_return(0.0)
-        datadog_rum_config[:sample_rate_percentage] = 0.0
+        datadog_rum_config.data[:sample_rate_percentage] = 0.0
         expect(include_datadog_rum_js?).to be(false)
       end
 
       it "returns false consistently when called multiple times" do
-        datadog_rum_config[:sample_rate_percentage] = 50.0
+        datadog_rum_config.data[:sample_rate_percentage] = 50.0
         allow(self).to receive(:random).and_return(0.6)
         expect(include_datadog_rum_js?).to be(false)
         allow(self).to receive(:random).and_return(0.4)
@@ -84,7 +84,7 @@ describe DatadogRumHelper do
       end
 
       it "returns true consistently when called multiple times" do
-        datadog_rum_config[:sample_rate_percentage] = 50.0
+        datadog_rum_config.data[:sample_rate_percentage] = 50.0
         allow(self).to receive(:random).and_return(0.4)
         expect(include_datadog_rum_js?).to be(true)
         allow(self).to receive(:random).and_return(0.6)
@@ -105,7 +105,7 @@ describe DatadogRumHelper do
 
       it "returns false when the sample rate percentage is 0.0" do
         request_datadog_rum_js
-        datadog_rum_config[:sample_rate_percentage] = 0.0
+        datadog_rum_config.data[:sample_rate_percentage] = 0.0
         expect(include_datadog_rum_js?).to be(false)
       end
 
@@ -122,19 +122,19 @@ describe DatadogRumHelper do
 
     it "returns false when the configuration is missing :application_id" do
       opt_in_datadog_rum_js
-      datadog_rum_config.delete(:application_id)
+      datadog_rum_config.data.delete(:application_id)
       expect(include_datadog_rum_js?).to be(false)
     end
 
     it "returns false when the configuration is missing :client_token" do
       opt_in_datadog_rum_js
-      datadog_rum_config.delete(:client_token)
+      datadog_rum_config.data.delete(:client_token)
       expect(include_datadog_rum_js?).to be(false)
     end
 
     it "returns false when the configuration is missing :sample_rate_percentage" do
       opt_in_datadog_rum_js
-      datadog_rum_config.delete(:sample_rate_percentage)
+      datadog_rum_config.data.delete(:sample_rate_percentage)
       expect(include_datadog_rum_js?).to be(false)
     end
   end