Add new Redis singleton to shard out feature flags

This also allow us to instrument feature-flag-specific Redis commands on the client side to help with sizing new Redis instance.

Add new Redis singleton to shard out feature flags
This also allow us to instrument feature-flag-specific Redis commands on the client side to help with sizing new Redis instance.
1fcfc5b3 · Sylvester Chin · Marius Bobin · b4ad4f1b · 1fcfc5b3 · 1fcfc5b3
--- a/lib/feature.rb
+++ b/lib/feature.rb
@@ -326,7 +326,7 @@ def l1_cache_backend
    end
    def l2_cache_backend
-      Rails.cache
+      ::Gitlab::Redis::FeatureFlag.cache_store
    end
    def log(key:, action:, **extra)

--- a/lib/gitlab/redis.rb
+++ b/lib/gitlab/redis.rb
@@ -10,6 +10,7 @@ module Redis
    ALL_CLASSES = [
      Gitlab::Redis::Cache,
      Gitlab::Redis::DbLoadBalancing,
+      Gitlab::Redis::FeatureFlag,
      Gitlab::Redis::Queues,
      Gitlab::Redis::RateLimiting,
      Gitlab::Redis::RepositoryCache,

--- a/lib/gitlab/redis/feature_flag.rb
+++ b/lib/gitlab/redis/feature_flag.rb
+# frozen_string_literal: true
+module Gitlab
+  module Redis
+    class FeatureFlag < ::Gitlab::Redis::Wrapper
+      FeatureFlagStore = Class.new(ActiveSupport::Cache::RedisCacheStore)
+      class << self
+        # The data we store on FeatureFlag is currently stored on Cache.
+        def config_fallback
+          Cache
+        end
+        def cache_store
+          @cache_store ||= FeatureFlagStore.new(
+            redis: pool,
+            compress: Gitlab::Utils.to_boolean(ENV.fetch('ENABLE_REDIS_CACHE_COMPRESSION', '1')),
+            namespace: Cache::CACHE_NAMESPACE,
+            expires_in: 1.hour
+          )
+        end
+      end
+    end
+  end
+end
--- a/spec/lib/feature_spec.rb
+++ b/spec/lib/feature_spec.rb
@@ -2,7 +2,7 @@
 require 'spec_helper'
-RSpec.describe Feature, stub_feature_flags: false, feature_category: :shared do
+RSpec.describe Feature, :clean_gitlab_redis_feature_flag, stub_feature_flags: false, feature_category: :shared do
  include StubVersion
  before do
@@ -212,7 +212,7 @@
    end
    it { expect(described_class.send(:l1_cache_backend)).to eq(Gitlab::ProcessMemoryCache.cache_backend) }
-    it { expect(described_class.send(:l2_cache_backend)).to eq(Rails.cache) }
+    it { expect(described_class.send(:l2_cache_backend)).to eq(Gitlab::Redis::FeatureFlag.cache_store) }
    it 'caches the status in L1 and L2 caches',
       :request_store, :use_clean_rails_memory_store_caching do

--- a/spec/lib/gitlab/redis/feature_flag_spec.rb
+++ b/spec/lib/gitlab/redis/feature_flag_spec.rb
+# frozen_string_literal: true
+require 'spec_helper'
+RSpec.describe Gitlab::Redis::FeatureFlag, feature_category: :redis do
+  include_examples "redis_new_instance_shared_examples", 'feature_flag', Gitlab::Redis::Cache
+  describe '.cache_store' do
+    it 'has a default ttl of 1 hour' do
+      expect(described_class.cache_store.options[:expires_in]).to eq(1.hour)
+    end
+  end
+end