Troubleshooting Common .NET HTTP Connection Errors

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The first is to identify whether the error is with the client or server (or even intermediaries). Most of the errors begin with “The underlying connection was closed: “…

Indications of client error

  • An unexpected error occurred on a send – Could be due to:
    • antivirus software installed on the client machine

 

Indications of intermediary error

  • The remote name could not be resolved or The proxy name could not be resolved – Could be due to:
    • DNS issue
    • inability to access the hosts file
  • Unable to connect to the remote server – Likely to have gotten through the DNS but hit a connection glitch due to:
    • proxy
    • firewall
    • network authentication

 

Indications of server error or intermediaries (e.g. load balancer, proxy, etc.)

  • An unexpected error occurred on a receive – Server or intermediary unexpectedly closes the TCP connection. May be due to:
    • Server or intermediary timeout values set too low (TODO: increase the client’s request timeout & also the server’s execution timeout such that client’s request timeout < intermediary’s < server’s)
    • Server crashes (TODO: check the server logs)
  • The request was canceled or The connection was closed unexpectedly – Server or intermediary cancels the TCP connection (TCP RSET). May be due to:
    • low (execution) timeout setting on the server or intermediary (TODO: increase the client’s request timeout & also the server’s execution timeout such that client’s request timeout < intermediary’s < server’s)
    • low keep-alive timeout setting on the server or intermediary (TODO: set client’s keep-alive timeout < intermediary’s < server’s)
    • Although improbable, it could be the result of insufficient concurrent connections at the client machine (typically defaulted to 2 by ServicePointManager.DefaultConnectionLimit). This is aggravated by slow processing at the server side
  • Could not establish trust relationship for the SSL/TLS secure channel -
    • Root and chain certificates are not installed correctly (TODO: install in the Local Machine store)
  • A connection that was expected to be kept alive was closed by the server – Server or intermediary closed the connection that is to be kept-alive due to:
    • client’s keep-alive timeout is longer than that of the server or intermediary (TODO: set client’s keep-alive timeout < intermediary’s < server’s)
  • The operation has timed out – Could be due to:
    • stale DNS entry for the proxy
    • socket timed-out before the response is returned (TODO: increase the client’s request timeout & read-write timeout. Increase the server’s execution timeout)
    • insufficient connection at the server such that no connection thread is available (TODO: increase server’s max connection to 12x number of processors)

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