Generalize Feature Flag system and implement unleash adapterimplement-unleash-client

This commit abstracts the current Feature implementation
and make it adoptable with any feature flag systems.

7 files changed, 242 insertions, 104 deletions

diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index 9a7859fc687..5af62576299 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -26,6 +26,7 @@ class ApplicationController < ActionController::Base
   before_action :require_email, unless: :devise_controller?
   before_action :set_usage_stats_consent_flag
   before_action :check_impersonation_availability
+  before_action :set_unleash_context
 
   around_action :set_locale
   around_action :set_session_storage
@@ -533,6 +534,16 @@ class ApplicationController < ActionController::Base
       yield
     end
   end
+
+  private
+
+  def set_unleash_context
+    @unleash_context = Unleash::Context.new(
+      session_id: session.id,
+      remote_address: request.remote_ip,
+      user_id: session[:user_id]
+    )
+  end
 end
 
 ApplicationController.prepend_if_ee('EE::ApplicationController')
diff --git a/config/gitlab.yml.example b/config/gitlab.yml.example
index 20b1020e025..c503102813d 100644
--- a/config/gitlab.yml.example
+++ b/config/gitlab.yml.example
@@ -463,6 +463,12 @@ production: &base
       # enabled: true
       # primary_api_url: http://localhost:5000/ # internal address to the primary registry, will be used by GitLab to directly communicate with primary registry API
 
+  ## Feature Flag
+  unleash:
+    # enabled: false
+    # url: https://gitlab.com/api/v4/feature_flags/unleash/<project_id>
+    # app_name: gitlab.com # Environment name of your GitLab instance
+    # instance_id: INSTNACE_ID
 
   #
   # 2. GitLab CI settings
diff --git a/config/initializers/1_settings.rb b/config/initializers/1_settings.rb
index 4160f488a7a..6e6d96d3f66 100644
--- a/config/initializers/1_settings.rb
+++ b/config/initializers/1_settings.rb
@@ -309,6 +309,14 @@ Gitlab.ee do
 end
 
 #
+# Unleash
+#
+Settings['unleash'] ||= Settingslogic.new({})
+Settings.unleash['enabled']      = false if Settings.unleash['enabled'].nil?
+Settings.unleash['app_name']     = Rails.env if Settings.unleash['app_name'].nil?
+Settings.unleash['instance_id']  = ENV['UNLEASH_INSTANCE_ID'] if Settings.unleash['instance_id'].nil?
+
+#
 # External merge request diffs
 #
 Settings['external_diffs'] ||= Settingslogic.new({})
diff --git a/config/initializers/flipper.rb b/config/initializers/flipper.rb
index 80cab7273e5..ddf9f3e8ab6 100644
--- a/config/initializers/flipper.rb
+++ b/config/initializers/flipper.rb
@@ -1 +1 @@
-Feature.register_feature_groups
+Gitlab::FeatureFlag::Adapters::Flipper.register_feature_groups
diff --git a/lib/feature.rb b/lib/feature.rb
index 88b0d871c3a..a5da331e49f 100644
--- a/lib/feature.rb
+++ b/lib/feature.rb
@@ -1,66 +1,21 @@
 # frozen_string_literal: true
 
-require 'flipper/adapters/active_record'
-require 'flipper/adapters/active_support_cache_store'
-
 class Feature
   prepend_if_ee('EE::Feature') # rubocop: disable Cop/InjectEnterpriseEditionModule
 
-  # Classes to override flipper table names
-  class FlipperFeature < Flipper::Adapters::ActiveRecord::Feature
-    # Using `self.table_name` won't work. ActiveRecord bug?
-    superclass.table_name = 'features'
-
-    def self.feature_names
-      pluck(:key)
-    end
-  end
-
-  class FlipperGate < Flipper::Adapters::ActiveRecord::Gate
-    superclass.table_name = 'feature_gates'
-  end
+  SUPPORTED_FEATURE_FLAG_ADAPTERS = %w[unleash flipper]
 
   class << self
-    delegate :group, to: :flipper
-
-    def all
-      flipper.features.to_a
-    end
+    delegate :all, :get, :enabled?, :remove, :group, to: :adapter
 
-    def get(key)
-      flipper.feature(key)
-    end
-
-    def persisted_names
-      Gitlab::SafeRequestStore[:flipper_persisted_names] ||=
-        begin
-          # We saw on GitLab.com, this database request was called 2300
-          # times/s. Let's cache it for a minute to avoid that load.
-          Gitlab::ThreadMemoryCache.cache_backend.fetch('flipper:persisted_names', expires_in: 1.minute) do
-            FlipperFeature.feature_names
-          end
+    def adapter
+      @adapter ||=
+        SUPPORTED_FEATURE_FLAG_ADAPTERS.find do |type|
+          adapter = get_adapter(type)
+          break adapter if adapter.available?
         end
     end
 
-    def persisted?(feature)
-      # Flipper creates on-memory features when asked for a not-yet-created one.
-      # If we want to check if a feature has been actually set, we look for it
-      # on the persisted features list.
-      persisted_names.include?(feature.name.to_s)
-    end
-
-    # use `default_enabled: true` to default the flag to being `enabled`
-    # unless set explicitly.  The default is `disabled`
-    def enabled?(key, thing = nil, default_enabled: false)
-      feature = Feature.get(key)
-
-      # If we're not default enabling the flag or the feature has been set, always evaluate.
-      # `persisted?` can potentially generate DB queries and also checks for inclusion
-      # in an array of feature names (177 at last count), possibly reducing performance by half.
-      # So we only perform the `persisted` check if `default_enabled: true`
-      !default_enabled || Feature.persisted?(feature) ? feature.enabled?(thing) : true
-    end
-
     def disabled?(key, thing = nil, default_enabled: false)
       # we need to make different method calls to make it easy to mock / define expectations in test mode
       thing.nil? ? !enabled?(key, default_enabled: default_enabled) : !enabled?(key, thing, default_enabled: default_enabled)
@@ -82,57 +37,10 @@ class Feature
       get(key).disable_group(group)
     end
 
-    def remove(key)
-      feature = get(key)
-      return unless persisted?(feature)
-
-      feature.remove
-    end
-
-    def flipper
-      if Gitlab::SafeRequestStore.active?
-        Gitlab::SafeRequestStore[:flipper] ||= build_flipper_instance
-      else
-        @flipper ||= build_flipper_instance
-      end
-    end
-
-    def build_flipper_instance
-      Flipper.new(flipper_adapter).tap { |flip| flip.memoize = true }
-    end
-
-    # This method is called from config/initializers/flipper.rb and can be used
-    # to register Flipper groups.
-    # See https://docs.gitlab.com/ee/development/feature_flags.html#feature-groups
-    def register_feature_groups
-    end
-
-    def flipper_adapter
-      active_record_adapter = Flipper::Adapters::ActiveRecord.new(
-        feature_class: FlipperFeature,
-        gate_class: FlipperGate)
-
-      # Redis L2 cache
-      redis_cache_adapter =
-        Flipper::Adapters::ActiveSupportCacheStore.new(
-          active_record_adapter,
-          l2_cache_backend,
-          expires_in: 1.hour)
-
-      # Thread-local L1 cache: use a short timeout since we don't have a
-      # way to expire this cache all at once
-      Flipper::Adapters::ActiveSupportCacheStore.new(
-        redis_cache_adapter,
-        l1_cache_backend,
-        expires_in: 1.minute)
-    end
-
-    def l1_cache_backend
-      Gitlab::ThreadMemoryCache.cache_backend
-    end
-
-    def l2_cache_backend
-      Rails.cache
+    private
+    
+    def get_adapter(type)
+      "Gitlab::FeatureFlag::Adapters::#{type.camelize}".constantize
     end
   end
 
diff --git a/lib/gitlab/feature_flag/adapters/flipper.rb b/lib/gitlab/feature_flag/adapters/flipper.rb
new file mode 100644
index 00000000000..869e073b2fd
--- /dev/null
+++ b/lib/gitlab/feature_flag/adapters/flipper.rb
@@ -0,0 +1,127 @@
+# frozen_string_literal: true
+
+require 'flipper/adapters/active_record'
+require 'flipper/adapters/active_support_cache_store'
+
+module Gitlab
+  module FeatureFlag
+    module Adapters
+      class Flipper
+        delegate :group, to: :flipper
+
+        # Classes to override flipper table names
+        class FlipperFeature < ::Flipper::Adapters::ActiveRecord::Feature
+          # Using `self.table_name` won't work. ActiveRecord bug?
+          superclass.table_name = 'features'
+
+          def self.feature_names
+            pluck(:key)
+          end
+        end
+
+        class FlipperGate < ::Flipper::Adapters::ActiveRecord::Gate
+          superclass.table_name = 'feature_gates'
+        end
+
+        class << self
+          def available?
+            true
+          end
+        
+          def all
+            flipper.features.to_a
+          end
+
+          def get(key)
+            flipper.feature(key)
+          end
+
+          # use `default_enabled: true` to default the flag to being `enabled`
+          # unless set explicitly.  The default is `disabled`
+          def enabled?(key, thing = nil, default_enabled: false)
+            feature = get(key)
+
+            # If we're not default enabling the flag or the feature has been set, always evaluate.
+            # `persisted?` can potentially generate DB queries and also checks for inclusion
+            # in an array of feature names (177 at last count), possibly reducing performance by half.
+            # So we only perform the `persisted` check if `default_enabled: true`
+            !default_enabled || persisted?(feature) ? feature.enabled?(thing) : true
+          end
+
+          def remove(key)
+            feature = get(key)
+            return unless persisted?(feature)
+      
+            feature.remove
+          end
+
+          # This method is called from config/initializers/flipper.rb and can be used
+          # to register Flipper groups.
+          # See https://docs.gitlab.com/ee/development/feature_flags.html#feature-groups
+          def register_feature_groups
+          end
+
+          private
+
+          def flipper
+            if Gitlab::SafeRequestStore.active?
+              Gitlab::SafeRequestStore[:flipper] ||= build_flipper_instance
+            else
+              @flipper ||= build_flipper_instance
+            end
+          end
+
+          def persisted_names
+            Gitlab::SafeRequestStore[:flipper_persisted_names] ||=
+              begin
+                # We saw on GitLab.com, this database request was called 2300
+                # times/s. Let's cache it for a minute to avoid that load.
+                Gitlab::ThreadMemoryCache.cache_backend.fetch('flipper:persisted_names', expires_in: 1.minute) do
+                  FlipperFeature.feature_names
+                end
+              end
+          end
+      
+          def persisted?(feature)
+            # Flipper creates on-memory features when asked for a not-yet-created one.
+            # If we want to check if a feature has been actually set, we look for it
+            # on the persisted features list.
+            persisted_names.include?(feature.name.to_s)
+          end
+
+          def build_flipper_instance
+            ::Flipper.new(flipper_adapter).tap { |flip| flip.memoize = true }
+          end
+
+          def flipper_adapter
+            active_record_adapter = ::Flipper::Adapters::ActiveRecord.new(
+              feature_class: FlipperFeature,
+              gate_class: FlipperGate)
+      
+            # Redis L2 cache
+            redis_cache_adapter =
+              ::Flipper::Adapters::ActiveSupportCacheStore.new(
+                active_record_adapter,
+                l2_cache_backend,
+                expires_in: 1.hour)
+      
+            # Thread-local L1 cache: use a short timeout since we don't have a
+            # way to expire this cache all at once
+            ::Flipper::Adapters::ActiveSupportCacheStore.new(
+              redis_cache_adapter,
+              l1_cache_backend,
+              expires_in: 1.minute)
+          end
+
+          def l1_cache_backend
+            Gitlab::ThreadMemoryCache.cache_backend
+          end
+      
+          def l2_cache_backend
+            Rails.cache
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/feature_flag/adapters/unleash.rb b/lib/gitlab/feature_flag/adapters/unleash.rb
new file mode 100644
index 00000000000..5e871d41996
--- /dev/null
+++ b/lib/gitlab/feature_flag/adapters/unleash.rb
@@ -0,0 +1,78 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module FeatureFlag
+    module Adapters
+      class Unleash
+        class Feature
+          def enable(key, thing = true)
+            # TODO:
+          end
+      
+          def disable(key, thing = false)
+            # TODO:
+          end
+      
+          def enable_group(key, group)
+            # Not Implemented yet
+          end
+      
+          def disable_group(key, group)
+            # Not Implemented yet
+          end
+
+          def remove
+            # TODO:
+          end
+
+          # new(Unleash::ToggleFetcher.toggle_cache[key])
+        end
+
+        class << self
+          def available?
+            Gitlab.config.unleash.enabled
+          end
+
+          def all
+            Unleash::ToggleFetcher.toggle_cache
+          end
+
+          def get(key)
+            Feature.get(key)
+          end
+
+          def enabled?(key, thing = nil, default_enabled: false)
+            feature = get(key)
+
+            # If we're not default enabling the flag or the feature has been set, always evaluate.
+            # `persisted?` can potentially generate DB queries and also checks for inclusion
+            # in an array of feature names (177 at last count), possibly reducing performance by half.
+            # So we only perform the `persisted` check if `default_enabled: true`
+            !default_enabled || persisted?(feature) ? feature.enabled?(thing) : true
+          end
+
+          def remove(key)
+            get(key).remove
+          end
+
+          def configure
+            ::Unleash.configure do |config|
+              config.url            = Gitlab.config.unleash.url
+              config.app_name       = Gitlab.config.unleash.app_name
+              config.instance_id    = Gitlab.config.unleash.instance_id
+              config.logger         = Logger.new(STDOUT)    # TODO: Structured logging
+              config.log_level      = Logger::DEBUG
+            end
+          end
+
+          private
+
+          def context
+            context = Unleash::Context.new
+            context.user_id = 123
+          end
+        end
+      end
+    end
+  end
+end