Painfully slow to unusable

It seems I have run into a problem again. After updating to Nop 4.0 I am having major speed issues with the site. Around 2pm every afternoon the site slows down so much that it is unusable. After checking the logs I am getting a varied array of issues. Here is a snap shot of the last few entries that seem to be of a certain ilk:

Error  The underlying connection was closed: An unexpected error occurred on a receive.  7/17/2018 4:03:43 PM  
  Error  Error 404. The requested page (/2-14-17) was not found  7/17/2018 3:57:33 PM  
  Error  Error 404. The requested page (/italjet) was not found  7/17/2018 3:54:54 PM  
  Error  Error 404. The requested page (/dunlop-kt355-2) was not found  7/17/2018 3:50:21 PM  
  Error  Error 404. The requested page (/bridgestone-exedra-max-em1r-7) was not found  7/17/2018 3:22:13 PM  
  Error  The underlying connection was closed: An unexpected error occurred on a receive.  7/17/2018 3:19:00 PM  
  Error  Error 404. The requested page (/bridgestone-s20fsz-evo-2) was not found  7/17/2018 3:17:45 PM  
  Information  Application started  7/17/2018 3:15:01 PM  
  Error  The remote server returned an error: (500) Internal Server Error.  7/17/2018 3:13:16 PM  
  Error  The remote server returned an error: (500) Internal Server Error.  7/17/2018 3:13:13 PM  
  Error  The remote server returned an error: (500) Internal Server Error.  7/17/2018 3:12:31 PM  
  Error  The underlying connection was closed: An unexpected error occurred on a receive.  7/17/2018 3:11:57 PM  
  Error  Exception of type 'System.OutOfMemoryException' was thrown.  7/17/2018 3:11:42 PM  
  Error  Exception of type 'System.OutOfMemoryException' was thrown.  7/17/2018 3:11:39 PM  
  Error  Exception of type 'System.OutOfMemoryException' was thrown.
Error  Exception of type 'System.OutOfMemoryException' was thrown.  7/17/2018 3:11:42 PM  
  Error  Exception of type 'System.OutOfMemoryException' was thrown.  7/17/2018 3:11:39 PM  
  Error  Exception of type 'System.OutOfMemoryException' was thrown.  7/17/2018 3:11:39 PM  
  Error  Exception of type 'System.OutOfMemoryException' was thrown.  7/17/2018 3:11:36 PM  
  Error  Exception of type 'System.OutOfMemoryException' was thrown.  7/17/2018 3:11:18 PM  
  Error  Exception of type 'System.OutOfMemoryException' was thrown.  7/17/2018 3:11:18 PM  
  Error  The underlying provider failed on Open.  7/17/2018 3:07:34 PM  
  Error  The underlying provider failed on Open.  7/17/2018 3:07:33 PM  
  Error  The underlying provider failed on Open.  7/17/2018 3:07:33 PM  
  Error  The underlying provider failed on Open.  7/17/2018 3:07:33 PM  
  Error  The underlying provider failed on Open.  7/17/2018 3:07:32 PM  
  Error  The underlying provider failed on Open.  7/17/2018 3:07:32 PM  
  Error  The underlying provider failed on Open.  7/17/2018 3:07:32 PM  
  Error  The underlying provider failed on Open.  7/17/2018 3:07:32 PM  
  Error  The underlying provider failed on Open.  7/17/2018 3:07:29 PM



and yet if you go back a page or two, the errors all seems to be page not found related:


  Error  Error 400. Bad request  7/17/2018 2:02:19 PM  
  Error  Error 400. Bad request  7/17/2018 2:02:16 PM  
  Error  Object reference not set to an instance of an object.  7/17/2018 2:01:58 PM  
  Error  Error 400. Bad request  7/17/2018 2:01:16 PM  
  Error  Error 404. The requested page (/index.php) was not found  7/17/2018 1:58:08 PM  
  Error  Error 404. The requested page (/bbs/forum.php) was not found  7/17/2018 1:58:02 PM  
  Error  Error 404. The requested page (/forum.php) was not found  7/17/2018 1:57:57 PM  
  Error  Error 404. The requested page (/plus/read.php) was not found  7/17/2018 1:57:51 PM  
  Error  Error 404. The requested page (/plus/ad_js.php) was not found  7/17/2018 1:57:46 PM  
  Error  Error 404. The requested page (/plus/download.php) was not found  7/17/2018 1:57:41 PM  
  Error  Error 404. The requested page (/plus/pbyynqucweku.php) was not found  7/17/2018 1:57:36 PM  
  Error  Error 404. The requested page (/include/dialog/select_soft_post.php) was not found  7/17/2018 1:57:31 PM  
  Error  Error 404. The requested page (/bridgestone-m204-7-2) was not found  7/17/2018 1:53:43 PM  
  Error  Error 404. The requested page (/dunlop-kt355-2) was not found  7/17/2018 1:50:18 PM  
  Error  Error 404. The requested page (/conti-twist-18-2) was not found


The website is at a complete standstill due to all these issues but I am not sure even where to start as most of the errors do not mean anything to me! Can anyone help please?

A number of those requests are for PHP pages which Nop is not written in. Could this be a hack or denial-of-service attempt from someone?

I would suggest turning on logging in IIS and see if the bad requests are originating from a small range of IP numbers.  You then have the option of blocking requests those IP numbers (again in IIS).

If this is caused by shenanigans from a third party then it might be worth talking to your hosting company and seeing what they can offer to prevent the requests before they even reach your server.

Another option might be to try Cloud Flare.  They offer a free package that helps block DDOS attacks and reduce server load (https://www.cloudflare.com/ddos/). I've not tried it with Nop though so don't know how well it fits.

Thank you for your reply! This is very useful information. Again right now the application server is so slow I cannot even access the logs via the admin area. I will investigate the Cloud flare avenue.

Thanks again

You can directly query the Log table in SQL Server (the IP addresses are in the record)