D, [2016-08-12T09:44:28.720794 #7409] DEBUG -- : accept: 999.999.999.999:60314
D, [2016-08-12T09:44:28.767776 #7409] DEBUG -- : Rack::Handler::WEBrick is invoked.
E, [2016-08-12T09:44:28.768114 #7409] ERROR -- : uninitialized constant Rack::Handler::WEBrick::RACK_VERSION
Did you mean?  Rack
               RUBY_VERSION (NameError)
/var/lib/gems/2.3.0/gems/rack-2.0.1/lib/rack/handler/webrick.rb:66:in `service'
/usr/lib/ruby/2.3.0/webrick/httpserver.rb:140:in `service'
/usr/lib/ruby/2.3.0/webrick/httpserver.rb:96:in `run'
/usr/lib/ruby/2.3.0/webrick/server.rb:296:in `block in start_thread'
D, [2016-08-12T09:44:28.771925 #7409] DEBUG -- : close: 999.999.999.999:60314