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Our .NET web app makes web service calls to Amazon S3 and to a partner system.

Out of nowhere, we've had two recent episodes where our web server starts to intermittently timeout on these calls. Logged error:

System.Net.WebException: Unable to connect to the remote server ---> System.Net.Sockets.SocketException: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond x.x.x.x:443 at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress) at System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Int32 timeout, Exception& exception) --- End of inner exception stack trace --- at System.Net.HttpWebRequest.GetRequestStream(TransportContext& context) at System.Net.HttpWebRequest.GetRequestStream() ...

We get a few timeout errors an hour (sometimes more; sometimes less - but each represents a failure to our users). In our first episode, the errors got gradually worse until we rebooted.

When the problem is in-effect, the Event Log shows absolutely nothing out of the ordinary. Task Manager > Networking peaks at about 25% utilization. From everything we can tell, the server is not overtaxed (CPU, files etc.); and everything looks normal.

The problem gets cleared up when we reboot (but apparently can start again at any time).

Any thoughts or suggestions would be most appreciated - including thoughts on logs we could check ... tools that we could run to monitor ... etc. Thanks!

Notes on our environment:

  • Win 2008 R2 Standard - OS Updates performed regularly
  • IIS 7.5 - App Pool is restarted nightly (but this hasn't helped)
  • .NET 4 web app - connects to a separate dedicated SQL Server machine
  • Dedicated firewall device (Win Firewall disabled)
  • Besides IIS, the only other installed software running is hMailServer and Symantec Endpoint Security
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I'd run perfmon and check your networking stats. Data throughput as well, but I'd be most interested in the number of concurrent connections and new connections being created. I've seen this before when the number of active connections gets "too high" for a server. I'd also be interested to see if maybe you're having small bursts of network activity that saturate your network connection for a short amount of time, until enough clients back off their requests (or timeout). Also, as a first troubleshooting step, disabling AV/firewall can very helpful. Turn off Symantec and see if that helps. –  HopelessN00b Genius of network Jul 24 '12 at 17:32
    
Thanks HopelessN00b! We will walk down this path. Sorry that I don't have enough points here to +1 your comment. –  Dave Clausen Jul 24 '12 at 18:39
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