Enable rack attack and add a throttle.

config/application.rb

@@ -77,5 +77,8 @@ module Gitlab
     # 3) In your unicorn.rb: ENV['RAILS_RELATIVE_URL_ROOT']
     #
     # config.relative_url_root = "/gitlab"
+
+    # Enable rack attack middleware
+    config.middleware.use Rack::Attack
   end
 end

config/initializers/rack_attack.rb

+Rack::Attack.throttle('user logins, registration and password reset', limit: 6, period: 60.seconds) do |req|
+  req.ip if ["/users/password", "/users/sign_in", "/users"].include?(req.path) && req.post?
+end