Add rate limiting to guard against excessive scheduling of pipelines

app/controllers/projects/pipeline_schedules_controller.rb

@@ -42,6 +42,13 @@ class Projects::PipelineSchedulesController < Projects::ApplicationController
   end
 
   def play
+    limiter = ::Gitlab::ActionRateLimiter.new(action: 'play_pipeline_schedule')
+
+    if limiter.throttled?(throttle_key, 1)
+      flash[:notice] = 'You cannot play this scheduled pipeline at the moment. Please wait a minute.'
+      return redirect_to pipeline_schedules_path(@project)
+    end
+
     job_id = RunPipelineScheduleWorker.perform_async(schedule.id, current_user.id)
 
     flash[:notice] =
@@ -74,6 +81,10 @@ class Projects::PipelineSchedulesController < Projects::ApplicationController
 
   private
 
+  def throttle_key
+    "user:#{current_user.id}:schedule:#{schedule.id}"
+  end
+
   def schedule
     @schedule ||= project.pipeline_schedules.find(params[:id])
   end

lib/gitlab/action_rate_limiter.rb

+module Gitlab
+  # This class implements a simple rate limiter that can be used to throttle
+  # certain actions. Unlike Rack Attack and Rack::Throttle, which operate at
+  # the middleware level, this can be used at the controller level.
+  class ActionRateLimiter
+    TIME_TO_EXPIRE = 60 # 1 min
+
+    attr_accessor :action, :expiry_time
+
+    def initialize(action:, expiry_time: TIME_TO_EXPIRE)
+      @action = action
+      @expiry_time = expiry_time
+    end
+
+    def increment(key)
+      value = 0
+
+      Gitlab::Redis::Cache.with do |redis|
+        cache_key = "action_rate_limiter:#{action}:#{key}"
+        value = redis.incr(cache_key)
+        redis.expire(cache_key, expiry_time) if value == 1
+      end
+
+      value.to_i
+    end
+
+    def throttled?(key, threshold_value)
+      self.increment(key) > threshold_value
+    end
+  end
+end

spec/controllers/projects/pipeline_schedules_controller_spec.rb

@@ -366,7 +366,7 @@ describe Projects::PipelineSchedulesController do
     end
   end
 
-  describe 'POST #play' do
+  describe 'POST #play', :clean_gitlab_redis_cache do
     set(:user) { create(:user) }
     let(:ref) { 'master' }