spread feature flag cache around a ring

Change-Id: I4831cc45d8646f6f86a34ade6546644c4dacdd49
Reviewed-on: https://gerrit.instructure.com/48065
Reviewed-by: Brian Palmer <brianp@instructure.com>
Tested-by: Jenkins
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>

app/controllers/feature_flags_controller.rb

@@ -232,7 +232,7 @@ class FeatureFlagsController < ApplicationController
       return render json: { message: "invalid feature" }, status: :bad_request unless feature_def
 
       # check whether the feature is locked
-      Rails.cache.delete(@context.feature_flag_cache_key(params[:feature]))
+      MultiCache.delete(@context.feature_flag_cache_key(params[:feature]), copies: MultiCache.copies('feature_flags'))
       current_flag = @context.lookup_feature_flag(params[:feature])
       if current_flag
         return render json: { message: "higher account disallows setting feature flag" }, status: :forbidden if current_flag.locked?(@context, @current_user)

app/models/feature_flag.rb

@@ -53,7 +53,7 @@ class FeatureFlag < ActiveRecord::Base
   end
 
   def clear_cache
-    connection.after_transaction_commit { Rails.cache.delete(self.context.feature_flag_cache_key(feature)) } if self.context
+    connection.after_transaction_commit { MultiCache.delete(self.context.feature_flag_cache_key(feature), copies: MultiCache.copies('feature_flags')) } if self.context
   end
 
 private

lib/feature_flags.rb

@@ -67,7 +67,7 @@ module FeatureFlags
   # (helper method.  use lookup_feature_flag to test policy.)
   def feature_flag(feature)
     self.shard.activate do
-      result = Rails.cache.fetch(feature_flag_cache_key(feature)) do
+      result = MultiCache.fetch(feature_flag_cache_key(feature), copies: MultiCache.copies('feature_flags')) do
         self.feature_flags.where(feature: feature.to_s).first || :nil
       end
       result = nil if result == :nil

spec/apis/v1/feature_flags_api_spec.rb

@@ -304,7 +304,7 @@ describe "Feature Flags API", type: :request do
       enable_cache do
         flag = t_root_account.feature_flags.create! feature: 'course_feature', state: 'on'
         # try to trick the controller into inserting (and violating a unique constraint) instead of updating
-        Rails.cache.write(cache_key, :nil)
+        MultiCache.fetch(cache_key) { :nil }
         api_call_as_user(t_root_admin, :put, "/api/v1/accounts/#{t_root_account.id}/features/flags/course_feature?state=off",
                          { controller: 'feature_flags', action: 'update', format: 'json', account_id: t_root_account.to_param, feature: 'course_feature', state: 'off' })
       end

spec/lib/feature_flags_spec.rb

@@ -286,7 +286,7 @@ describe FeatureFlags do
   end
 
   describe "caching" do
-    let(:t_cache_key) { t_root_account.feature_flag_cache_key('course_feature') }
+    let(:t_cache_key) { "#{t_root_account.feature_flag_cache_key('course_feature')}:0" }
     before do
       t_root_account.feature_flags.create! feature: 'course_feature', state: 'allowed'
     end
@@ -301,7 +301,7 @@ describe FeatureFlags do
     it "should cache a nil result" do
       enable_cache do
         t_root_account.feature_flag('course_feature2')
-        expect(Rails.cache).to be_exist(t_root_account.feature_flag_cache_key('course_feature2'))
+        expect(Rails.cache).to be_exist("#{t_root_account.feature_flag_cache_key('course_feature2')}:0")
         t_root_account.expects(:feature_flags).never
         t_root_account.feature_flag('course_feature2')
       end