Add feature toggles through Flipper

Gemfile

@@ -370,3 +370,7 @@ gem 'sys-filesystem', '~> 1.1.6'
 gem 'gitaly', '~> 0.7.0'
 
 gem 'toml-rb', '~> 0.3.15', require: false
+
+# Feature toggles
+gem 'flipper', '~> 0.10.2'
+gem 'flipper-active_record', '~> 0.10.2'

Gemfile.lock

@@ -206,6 +206,10 @@ GEM
       path_expander (~> 1.0)
       ruby_parser (~> 3.0)
       sexp_processor (~> 4.0)
+    flipper (0.10.2)
+    flipper-active_record (0.10.2)
+      activerecord (>= 3.2, < 6)
+      flipper (~> 0.10.2)
     flowdock (0.7.1)
       httparty (~> 0.7)
       multi_json
@@ -907,6 +911,8 @@ DEPENDENCIES
   faraday (~> 0.11.0)
   ffaker (~> 2.4)
   flay (~> 2.8.0)
+  flipper (~> 0.10.2)
+  flipper-active_record (~> 0.10.2)
   fog-aws (~> 0.9)
   fog-core (~> 1.44)
   fog-google (~> 0.5)

changelogs/unreleased/feature-flags-flipper.yml

+---
+title: Add feature toggles and API endpoints for admins
+merge_request: 11747
+author:

db/migrate/20170525174156_create_feature_tables.rb

+class CreateFeatureTables < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def self.up
+    create_table :features do |t|
+      t.string :key, null: false
+      t.timestamps null: false
+    end
+    add_index :features, :key, unique: true
+
+    create_table :feature_gates do |t|
+      t.string :feature_key, null: false
+      t.string :key, null: false
+      t.string :value
+      t.timestamps null: false
+    end
+    add_index :feature_gates, [:feature_key, :key, :value], unique: true
+  end
+
+  def self.down
+    drop_table :feature_gates
+    drop_table :features
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20170523091700) do
+ActiveRecord::Schema.define(version: 20170525174156) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -440,6 +440,24 @@ ActiveRecord::Schema.define(version: 20170523091700) do
   add_index "events", ["target_id"], name: "index_events_on_target_id", using: :btree
   add_index "events", ["target_type"], name: "index_events_on_target_type", using: :btree
 
+  create_table "feature_gates", force: :cascade do |t|
+    t.string "feature_key", null: false
+    t.string "key", null: false
+    t.string "value"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+  end
+
+  add_index "feature_gates", ["feature_key", "key", "value"], name: "index_feature_gates_on_feature_key_and_key_and_value", unique: true, using: :btree
+
+  create_table "features", force: :cascade do |t|
+    t.string "key", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+  end
+
+  add_index "features", ["key"], name: "index_features_on_key", unique: true, using: :btree
+
   create_table "forked_project_links", force: :cascade do |t|
     t.integer "forked_to_project_id", null: false
     t.integer "forked_from_project_id", null: false

doc/api/features.md

+# Features API
+
+All methods require administrator authorization.
+
+Notice that currently the API only supports boolean and percentage-of-time gate
+values.
+
+## List all features
+
+Get a list of all persisted features, with its gate values.
+
+```
+GET /features
+```
+
+```bash
+curl --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v4/features
+```
+
+Example response:
+
+```json
+[
+  {
+    "name": "experimental_feature",
+    "state": "off",
+    "gates": [
+      {
+        "key": "boolean",
+        "value": false
+      }
+    ]
+  },
+  {
+    "name": "new_library",
+    "state": "on",
+    "gates": [
+      {
+        "key": "boolean",
+        "value": true
+      }
+    ]
+  }
+]
+```
+
+## Set or create a feature
+
+Set a feature's gate value. If a feature with the given name doesn't exist yet
+it will be created. The value can be a boolean, or an integer to indicate
+percentage of time.
+
+```
+POST /features/:name
+```
+
+| Attribute | Type | Required | Description |
+| --------- | ---- | -------- | ----------- |
+| `name` | string | yes | Name of the feature to create or update |
+| `value` | integer/string | yes | `true` or `false` to enable/disable, or an integer for percentage of time |
+
+```bash
+curl --data "value=30" --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v4/features/new_library
+```
+
+Example response:
+
+```json
+{
+  "name": "new_library",
+  "state": "conditional",
+  "gates": [
+    {
+      "key": "boolean",
+      "value": false
+    },
+    {
+      "key": "percentage_of_time",
+      "value": 30
+    }
+  ]
+}
+```

doc/development/README.md

@@ -42,6 +42,7 @@
 - [Sidekiq debugging](sidekiq_debugging.md)
 - [Object state models](object_state_models.md)
 - [Building a package for testing purposes](build_test_package.md)
+- [Manage feature flags](feature_flags.md)
 
 ## Databases
 

doc/development/feature_flags.md

+# Manage feature flags
+
+Starting from GitLab 9.3 we support feature flags via
+[Flipper](https://github.com/jnunemaker/flipper/). You should use the `Feature`
+class (defined in `lib/feature.rb`) in your code to get, set and list feature
+flags. During runtime you can set the values for the gates via the
+[admin API](../api/features.md).

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

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

lib/api/features.rb

+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

lib/feature.rb

+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

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)

spec/lib/feature_spec.rb

+require 'spec_helper'
+
+describe Feature, lib: true do
+  describe '.get' do
+    let(:feature) { double(:feature) }
+    let(:key) { 'my_feature' }
+
+    it 'returns the Flipper feature' do
+      expect_any_instance_of(Flipper::DSL).to receive(:feature).with(key).
+        and_return(feature)
+
+      expect(described_class.get(key)).to be(feature)
+    end
+  end
+
+  describe '.all' do
+    let(:features) { Set.new }
+
+    it 'returns the Flipper features as an array' do
+      expect_any_instance_of(Flipper::DSL).to receive(:features).
+        and_return(features)
+
+      expect(described_class.all).to eq(features.to_a)
+    end
+  end
+end

spec/lib/gitlab/gitaly_client_spec.rb

 require 'spec_helper'
 
-describe Gitlab::GitalyClient, lib: true do
+# We stub Gitaly in `spec/support/gitaly.rb` for other tests. We don't want
+# those stubs while testing the GitalyClient itself.
+describe Gitlab::GitalyClient, lib: true, skip_gitaly_mock: true do
   describe '.stub' do
+    # Notice that this is referring to gRPC "stubs", not rspec stubs
     before { described_class.clear_stubs! }
 
     context 'when passed a UNIX socket address' do
@@ -32,4 +35,81 @@ describe Gitlab::GitalyClient, lib: true do
       end
     end
   end
+
+  describe 'feature_enabled?' do
+    let(:feature_name) { 'my_feature' }
+    let(:real_feature_name) { "gitaly_#{feature_name}" }
+
+    context 'when Gitaly is disabled' do
+      before { allow(described_class).to receive(:enabled?).and_return(false) }
+
+      it 'returns false' do
+        expect(described_class.feature_enabled?(feature_name)).to be(false)
+      end
+    end
+
+    context 'when the feature status is DISABLED' do
+      let(:feature_status) { Gitlab::GitalyClient::MigrationStatus::DISABLED }
+
+      it 'returns false' do
+        expect(described_class.feature_enabled?(feature_name, status: feature_status)).to be(false)
+      end
+    end
+
+    context 'when the feature_status is OPT_IN' do
+      let(:feature_status) { Gitlab::GitalyClient::MigrationStatus::OPT_IN }
+
+      context "when the feature flag hasn't been set" do
+        it 'returns false' do
+          expect(described_class.feature_enabled?(feature_name, status: feature_status)).to be(false)
+        end
+      end
+
+      context "when the feature flag is set to disable" do
+        before { Feature.get(real_feature_name).disable }
+
+        it 'returns false' do
+          expect(described_class.feature_enabled?(feature_name, status: feature_status)).to be(false)
+        end
+      end
+
+      context "when the feature flag is set to enable" do
+        before { Feature.get(real_feature_name).enable }
+
+        it 'returns true' do
+          expect(described_class.feature_enabled?(feature_name, status: feature_status)).to be(true)
+        end
+      end
+
+      context "when the feature flag is set to a percentage of time" do
+        before { Feature.get(real_feature_name).enable_percentage_of_time(70) }
+
+        it 'bases the result on pseudo-random numbers' do
+          expect(Random).to receive(:rand).and_return(0.3)
+          expect(described_class.feature_enabled?(feature_name, status: feature_status)).to be(true)
+
+          expect(Random).to receive(:rand).and_return(0.8)
+          expect(described_class.feature_enabled?(feature_name, status: feature_status)).to be(false)
+        end
+      end
+    end
+
+    context 'when the feature_status is OPT_OUT' do
+      let(:feature_status) { Gitlab::GitalyClient::MigrationStatus::OPT_OUT }
+
+      context "when the feature flag hasn't been set" do
+        it 'returns true' do
+          expect(described_class.feature_enabled?(feature_name, status: feature_status)).to be(true)
+        end
+      end
+
+      context "when the feature flag is set to disable" do
+        before { Feature.get(real_feature_name).disable }
+
+        it 'returns false' do
+          expect(described_class.feature_enabled?(feature_name, status: feature_status)).to be(false)
+        end
+      end
+    end
+  end
 end

spec/requests/api/features_spec.rb

+require 'spec_helper'
+
+describe API::Features do
+  let(:user)  { create(:user) }
+  let(:admin) { create(:admin) }
+
+  describe 'GET /features' do
+    let(:expected_features) do
+      [
+        {
+          'name' => 'feature_1',
+          'state' => 'on',
+          'gates' => [{ 'key' => 'boolean', 'value' => true }]
+        },
+        {
+          'name' => 'feature_2',
+          'state' => 'off',
+          'gates' => [{ 'key' => 'boolean', 'value' => false }]
+        }
+      ]
+    end
+
+    before do
+      Feature.get('feature_1').enable
+      Feature.get('feature_2').disable
+    end
+
+    it 'returns a 401 for anonymous users' do
+      get api('/features')
+
+      expect(response).to have_http_status(401)
+    end
+
+    it 'returns a 403 for users' do
+      get api('/features', user)
+
+      expect(response).to have_http_status(403)
+    end
+
+    it 'returns the feature list for admins' do
+      get api('/features', admin)
+
+      expect(response).to have_http_status(200)
+      expect(json_response).to match_array(expected_features)
+    end
+  end
+
+  describe 'POST /feature' do
+    let(:feature_name) { 'my_feature' }
+    it 'returns a 401 for anonymous users' do
+      post api("/features/#{feature_name}")
+
+      expect(response).to have_http_status(401)
+    end
+
+    it 'returns a 403 for users' do
+      post api("/features/#{feature_name}", user)
+
+      expect(response).to have_http_status(403)
+    end
+
+    it 'creates an enabled feature if passed true' do
+      post api("/features/#{feature_name}", admin), value: 'true'
+
+      expect(response).to have_http_status(201)
+      expect(Feature.get(feature_name)).to be_enabled
+    end
+
+    it 'creates a feature with the given percentage if passed an integer' do
+      post api("/features/#{feature_name}", admin), value: '50'
+
+      expect(response).to have_http_status(201)
+      expect(Feature.get(feature_name).percentage_of_time_value).to be(50)
+    end
+
+    context 'when the feature exists' do
+      let(:feature) { Feature.get(feature_name) }
+
+      before do
+        feature.disable # This also persists the feature on the DB
+      end
+
+      it 'enables the feature if passed true' do
+        post api("/features/#{feature_name}", admin), value: 'true'
+
+        expect(response).to have_http_status(201)
+        expect(feature).to be_enabled
+      end
+
+      context 'with a pre-existing percentage value' do
+        before do
+          feature.enable_percentage_of_time(50)
+        end
+
+        it 'updates the percentage of time if passed an integer' do
+          post api("/features/#{feature_name}", admin), value: '30'
+
+          expect(response).to have_http_status(201)
+          expect(Feature.get(feature_name).percentage_of_time_value).to be(30)
+        end
+      end
+    end
+  end
+end

spec/support/gitaly.rb

 if Gitlab::GitalyClient.enabled?
   RSpec.configure do |config|
-    config.before(:each) do
+    config.before(:each) do |example|
+      next if example.metadata[:skip_gitaly_mock]
       allow(Gitlab::GitalyClient).to receive(:feature_enabled?).and_return(true)
     end
   end