Extracted source (around line #115):

      subscribe_to(Event::PRIMARY_ELECTED, Event::PrimaryElected.new(self))

      seeds.each{ |seed| add(seed) }
      ObjectSpace.define_finalizer(self, self.class.finalize(pools))
    end

full trace

vendor/bundle/ruby/2.2.0/gems/mongo-2.2.5/lib/mongo/cluster.rb:115:in `initialize'
vendor/bundle/ruby/2.2.0/gems/mongo-2.2.5/lib/mongo/client.rb:337:in `new'
vendor/bundle/ruby/2.2.0/gems/mongo-2.2.5/lib/mongo/client.rb:337:in `create_from_addresses'
vendor/bundle/ruby/2.2.0/gems/mongo-2.2.5/lib/mongo/client.rb:202:in `initialize'
vendor/bundle/ruby/2.2.0/gems/mongoid-5.1.3/lib/mongoid/clients/factory.rb:64:in `new'
vendor/bundle/ruby/2.2.0/gems/mongoid-5.1.3/lib/mongoid/clients/factory.rb:64:in `create_client'
vendor/bundle/ruby/2.2.0/gems/mongoid-5.1.3/lib/mongoid/clients/factory.rb:27:in `create'
vendor/bundle/ruby/2.2.0/gems/mongoid-5.1.3/lib/mongoid/clients.rb:66:in `with_name'
vendor/bundle/ruby/2.2.0/gems/mongoid-5.1.3/lib/mongoid/clients.rb:115:in `mongo_client'
vendor/bundle/ruby/2.2.0/gems/mongoid-5.1.3/lib/mongoid/clients.rb:135:in `collection'
vendor/bundle/ruby/2.2.0/gems/mongoid-5.1.3/lib/mongoid/clients/options.rb:283:in `method_missing'
vendor/bundle/ruby/2.2.0/gems/mongoid-5.1.3/lib/mongoid/contextual/mongo.rb:313:in `initialize'
vendor/bundle/ruby/2.2.0/gems/mongoid-5.1.3/lib/mongoid/contextual.rb:53:in `new'
vendor/bundle/ruby/2.2.0/gems/mongoid-5.1.3/lib/mongoid/contextual.rb:53:in `create_context'
vendor/bundle/ruby/2.2.0/gems/mongoid-5.1.3/lib/mongoid/contextual.rb:35:in `context'
vendor/bundle/ruby/2.2.0/gems/mongoid-5.1.3/lib/mongoid/contextual.rb:20:in `first'
vendor/bundle/ruby/2.2.0/gems/locomotivecms-3.1.1/lib/locomotive/middlewares/site.rb:87:in `fetch_from_host'
vendor/bundle/ruby/2.2.0/gems/locomotivecms-3.1.1/lib/locomotive/middlewares/site.rb:45:in `fetch_site'
vendor/bundle/ruby/2.2.0/gems/locomotivecms-3.1.1/lib/locomotive/middlewares/site.rb:19:in `call'
vendor/bundle/ruby/2.2.0/gems/dragonfly-1.0.12/lib/dragonfly/middleware.rb:14:in `call'
vendor/bundle/ruby/2.2.0/gems/warden-1.2.6/lib/warden/manager.rb:35:in `block in call'
vendor/bundle/ruby/2.2.0/gems/warden-1.2.6/lib/warden/manager.rb:34:in `catch'
vendor/bundle/ruby/2.2.0/gems/warden-1.2.6/lib/warden/manager.rb:34:in `call'
vendor/bundle/ruby/2.2.0/gems/rack-1.6.4/lib/rack/etag.rb:24:in `call'
vendor/bundle/ruby/2.2.0/gems/rack-1.6.4/lib/rack/conditionalget.rb:25:in `call'
vendor/bundle/ruby/2.2.0/gems/rack-1.6.4/lib/rack/head.rb:13:in `call'
vendor/bundle/ruby/2.2.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/params_parser.rb:27:in `call'
vendor/bundle/ruby/2.2.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/flash.rb:260:in `call'
vendor/bundle/ruby/2.2.0/gems/rack-1.6.4/lib/rack/session/abstract/id.rb:225:in `context'
vendor/bundle/ruby/2.2.0/gems/rack-1.6.4/lib/rack/session/abstract/id.rb:220:in `call'
vendor/bundle/ruby/2.2.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/cookies.rb:560:in `call'
vendor/bundle/ruby/2.2.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:88:in `__run_callbacks__'
vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:778:in `_run_call_callbacks'
vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:81:in `run_callbacks'
vendor/bundle/ruby/2.2.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/callbacks.rb:27:in `call'
vendor/bundle/ruby/2.2.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/remote_ip.rb:78:in `call'
vendor/bundle/ruby/2.2.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
vendor/bundle/ruby/2.2.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/rack/logger.rb:38:in `call_app'
vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/rack/logger.rb:20:in `block in call'
vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/tagged_logging.rb:68:in `block in tagged'
vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/tagged_logging.rb:26:in `tagged'
vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/tagged_logging.rb:68:in `tagged'
vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/rack/logger.rb:20:in `call'
vendor/bundle/ruby/2.2.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/request_id.rb:21:in `call'
vendor/bundle/ruby/2.2.0/gems/rack-1.6.4/lib/rack/methodoverride.rb:22:in `call'
vendor/bundle/ruby/2.2.0/gems/rack-1.6.4/lib/rack/runtime.rb:18:in `call'
vendor/bundle/ruby/2.2.0/gems/locomotivecms-3.1.1/lib/locomotive/middlewares/image_thumbnail.rb:23:in `call'
vendor/bundle/ruby/2.2.0/gems/dragonfly-1.0.12/lib/dragonfly/cookie_monster.rb:9:in `call'
vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/cache/strategy/local_cache_middleware.rb:28:in `call'
vendor/bundle/ruby/2.2.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/static.rb:120:in `call'
vendor/bundle/ruby/2.2.0/gems/rack-1.6.4/lib/rack/sendfile.rb:113:in `call'
vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/engine.rb:518:in `call'
vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/application.rb:165:in `call'
vendor/bundle/ruby/2.2.0/gems/puma-2.15.3/lib/puma/configuration.rb:79:in `call'
vendor/bundle/ruby/2.2.0/gems/puma-2.15.3/lib/puma/server.rb:541:in `handle_request'
vendor/bundle/ruby/2.2.0/gems/puma-2.15.3/lib/puma/server.rb:388:in `process_client'
vendor/bundle/ruby/2.2.0/gems/puma-2.15.3/lib/puma/server.rb:270:in `block in run'
vendor/bundle/ruby/2.2.0/gems/puma-2.15.3/lib/puma/thread_pool.rb:106:in `call'
vendor/bundle/ruby/2.2.0/gems/puma-2.15.3/lib/puma/thread_pool.rb:106:in `block in spawn_thread'