Add latest changes from gitlab-org/gitlab@master

3 files changed, 112 insertions, 13 deletions

diff --git a/app/experiments/application_experiment.rb b/app/experiments/application_experiment.rb
index 1c9a3c5f37f..663c58ceda6 100644
--- a/app/experiments/application_experiment.rb
+++ b/app/experiments/application_experiment.rb
@@ -23,16 +23,41 @@ class ApplicationExperiment < Gitlab::Experiment # rubocop:disable Gitlab/Namesp
     ))
   end
 
+  def rollout_strategy
+    # no-op override in inherited class as desired
+  end
+
+  def variants
+    # override as desired in inherited class with all variants + control
+    # %i[variant1 variant2 control]
+    #
+    # this will make sure we supply variants as these go together - rollout_strategy of :round_robin must have variants
+    raise NotImplementedError, "Inheriting class must supply variants as an array if :round_robin strategy is used" if rollout_strategy == :round_robin
+  end
+
   private
 
+  def feature_flag_name
+    name.tr('/', '_')
+  end
+
   def resolve_variant_name
-    return variant_names.first if Feature.enabled?(feature_flag_name, self, type: :experiment, default_enabled: :yaml)
+    case rollout_strategy
+    when :round_robin
+      round_robin_rollout
+    else
+      percentage_rollout
+    end
+  end
 
-    nil # Returning nil vs. :control is important for not caching and rollouts.
+  def round_robin_rollout
+    Strategy::RoundRobin.new(feature_flag_name, variants).execute
   end
 
-  def feature_flag_name
-    name.tr('/', '_')
+  def percentage_rollout
+    return variant_names.first if Feature.enabled?(feature_flag_name, self, type: :experiment, default_enabled: :yaml)
+
+    nil # Returning nil vs. :control is important for not caching and rollouts.
   end
 
   # Cache is an implementation on top of Gitlab::Redis::SharedState that also
diff --git a/app/experiments/members/invite_email_experiment.rb b/app/experiments/members/invite_email_experiment.rb
index 58703fd505d..4a03ebb7726 100644
--- a/app/experiments/members/invite_email_experiment.rb
+++ b/app/experiments/members/invite_email_experiment.rb
@@ -7,16 +7,12 @@ module Members
 
     INVITE_TYPE = 'initial_email'
 
-    private
+    def rollout_strategy
+      :round_robin
+    end
 
-    def resolve_variant_name
-      # we are overriding here so that when we add another experiment
-      # we can merely add that variant and check of feature flag here
-      if Feature.enabled?(feature_flag_name, self, type: :experiment, default_enabled: :yaml)
-        :avatar
-      else
-        nil # :control
-      end
+    def variants
+      %i[avatar permission_info control]
     end
   end
 end
diff --git a/app/experiments/strategy/round_robin.rb b/app/experiments/strategy/round_robin.rb
new file mode 100644
index 00000000000..7b80c0e984d
--- /dev/null
+++ b/app/experiments/strategy/round_robin.rb
@@ -0,0 +1,78 @@
+# frozen_string_literal: true
+
+module Strategy
+  class RoundRobin
+    CacheError = Class.new(StandardError)
+
+    COUNTER_EXPIRE_TIME = 86400 # one day
+
+    def initialize(key, variants)
+      @key = key
+      @variants = variants
+    end
+
+    def execute
+      increment_counter
+      resolve_variant_name
+    end
+
+    # When the counter would expire
+    #
+    # @api private Used internally by SRE and debugging purpose
+    # @return [Integer] Number in seconds until expiration or false if never
+    def counter_expires_in
+      Gitlab::Redis::SharedState.with do |redis|
+        redis.ttl(key)
+      end
+    end
+
+    # Return the actual counter value
+    #
+    # @return [Integer] value
+    def counter_value
+      Gitlab::Redis::SharedState.with do |redis|
+        (redis.get(key) || 0).to_i
+      end
+    end
+
+    # Reset the counter
+    #
+    # @private Used internally by SRE and debugging purpose
+    # @return [Boolean] whether reset was a success
+    def reset!
+      redis_cmd do |redis|
+        redis.del(key)
+      end
+    end
+
+    private
+
+    attr_reader :key, :variants
+
+    # Increase the counter
+    #
+    # @return [Boolean] whether operation was a success
+    def increment_counter
+      redis_cmd do |redis|
+        redis.incr(key)
+        redis.expire(key, COUNTER_EXPIRE_TIME)
+      end
+    end
+
+    def resolve_variant_name
+      remainder = counter_value % variants.size
+
+      variants[remainder]
+    end
+
+    def redis_cmd
+      Gitlab::Redis::SharedState.with { |redis| yield(redis) }
+
+      true
+    rescue CacheError => e
+      Gitlab::AppLogger.warn("GitLab: An unexpected error occurred in writing to Redis: #{e}")
+
+      false
+    end
+  end
+end