Add feature toggles through Flipper

5 files changed, 120 insertions, 2 deletions

diff --git a/lib/api/api.rb b/lib/api/api.rb
index bbdd2039f43..7ae2f3cad40 100644
--- a/lib/api/api.rb
+++ b/lib/api/api.rb
@@ -94,6 +94,7 @@ module API
     mount ::API::DeployKeys
     mount ::API::Deployments
     mount ::API::Environments
+    mount ::API::Features
     mount ::API::Files
     mount ::API::Groups
     mount ::API::Internal
diff --git a/lib/api/entities.rb b/lib/api/entities.rb
index e10bd230ae2..fc8183a62c1 100644
--- a/lib/api/entities.rb
+++ b/lib/api/entities.rb
@@ -753,6 +753,28 @@ module API
       expose :impersonation
     end
 
+    class FeatureGate < Grape::Entity
+      expose :key
+      expose :value
+    end
+
+    class Feature < Grape::Entity
+      expose :name
+      expose :state
+      expose :gates, using: FeatureGate do |model|
+        model.gates.map do |gate|
+          value = model.gate_values[gate.key]
+
+          # By default all gate values are populated. Only show relevant ones.
+          if (value.is_a?(Integer) && value.zero?) || (value.is_a?(Set) && value.empty?)
+            next
+          end
+
+          { key: gate.key, value: value }
+        end.compact
+      end
+    end
+
     module JobRequest
       class JobInfo < Grape::Entity
         expose :name, :stage
diff --git a/lib/api/features.rb b/lib/api/features.rb
new file mode 100644
index 00000000000..cff0ba2ddff
--- /dev/null
+++ b/lib/api/features.rb
@@ -0,0 +1,36 @@
+module API
+  class Features < Grape::API
+    before { authenticated_as_admin! }
+
+    resource :features do
+      desc 'Get a list of all features' do
+        success Entities::Feature
+      end
+      get do
+        features = Feature.all
+
+        present features, with: Entities::Feature, current_user: current_user
+      end
+
+      desc 'Set the gate value for the given feature' do
+        success Entities::Feature
+      end
+      params do
+        requires :value, type: String, desc: '`true` or `false` to enable/disable, an integer for percentage of time'
+      end
+      post ':name' do
+        feature = Feature.get(params[:name])
+
+        if %w(0 false).include?(params[:value])
+          feature.disable
+        elsif params[:value] == 'true'
+          feature.enable
+        else
+          feature.enable_percentage_of_time(params[:value].to_i)
+        end
+
+        present feature, with: Entities::Feature, current_user: current_user
+      end
+    end
+  end
+end
diff --git a/lib/feature.rb b/lib/feature.rb
new file mode 100644
index 00000000000..2e2b343f82c
--- /dev/null
+++ b/lib/feature.rb
@@ -0,0 +1,41 @@
+require 'flipper/adapters/active_record'
+
+class Feature
+  # 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'
+  end
+
+  class FlipperGate < Flipper::Adapters::ActiveRecord::Gate
+    superclass.table_name = 'feature_gates'
+  end
+
+  class << self
+    def all
+      flipper.features.to_a
+    end
+
+    def get(key)
+      flipper.feature(key)
+    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.
+      all.map(&:name).include?(feature.name)
+    end
+
+    private
+
+    def flipper
+      @flipper ||= begin
+        adapter = Flipper::Adapters::ActiveRecord.new(
+          feature_class: FlipperFeature, gate_class: FlipperGate)
+
+        Flipper.new(adapter)
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/gitaly_client.rb b/lib/gitlab/gitaly_client.rb
index 72466700c05..2343446bf22 100644
--- a/lib/gitlab/gitaly_client.rb
+++ b/lib/gitlab/gitaly_client.rb
@@ -2,6 +2,12 @@ require 'gitaly'
 
 module Gitlab
   module GitalyClient
+    module MigrationStatus
+      DISABLED = 1
+      OPT_IN = 2
+      OPT_OUT = 3
+    end
+
     SERVER_VERSION_FILE = 'GITALY_SERVER_VERSION'.freeze
 
     MUTEX = Mutex.new
@@ -46,8 +52,20 @@ module Gitlab
       Gitlab.config.gitaly.enabled
     end
 
-    def self.feature_enabled?(feature)
-      enabled? && ENV["GITALY_#{feature.upcase}"] == '1'
+    def self.feature_enabled?(feature, status: MigrationStatus::OPT_IN)
+      return false if !enabled? || status == MigrationStatus::DISABLED
+
+      feature = Feature.get("gitaly_#{feature}")
+
+      # If the feature hasn't been set, turn it on if it's opt-out
+      return status == MigrationStatus::OPT_OUT unless Feature.persisted?(feature)
+
+      if feature.percentage_of_time_value > 0
+        # Probabilistically enable this feature
+        return Random.rand() * 100 < feature.percentage_of_time_value
+      end
+
+      feature.enabled?
     end
 
     def self.migrate(feature)