如何解决 C# IIS 托管 WCF NET TCP 服务超时问题

Question

I have inherited a C# web service hosted by IIS on Windows Server 2019 that is having a problem that I'm struggling to track down.

The WCF service listens on port 82 for http connections, and on port 8002 for net tcp connections; the IIS config for the site has it's Bindings set to http:*:82:,net.tcp:8002:*

However, when the service has been running for a few hours it stops responding on the net tcp port (8002) - other apps that attempt to connect to it end up timing out:

System.TimeoutException: The open operation did not complete within the allotted timeout of 00:01:00. The time allotted to this operation may have been a portion of a longer timeout. ---> System.TimeoutException: The socket transfer timed out after 00:01:00. You have exceeded the timeout set on your binding. The time allotted to this operation may have been a portion of a longer timeout. ---> 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

Yet connections to the http port (82) still work as expected, so the service is still running.

Recycling the appropriate app pool causes the net tcp connections to start working properly again, which suggests to me that it might be some sort of resource leak, but I can see nothing obvious in the code, and it doesn't appear to be a lack of memory.

I'm at a loss as to how to troubleshoot this further - any suggestions?

Answer 1

According to your description, the problem may be that the number of connected clients exceeds the maximum capacity of the server-side, and the server can't handle it. If the client-side waits for a timeout, the TimeoutException will appear.

You can view the maximum number of connections for the service through the following code:

        NetTcpBinding binding = new NetTcpBinding();
        Console.WriteLine(binding.MaxConnections);

This is a reference link for maxconnections:

https://docs.microsoft.com/en-us/dotnet/api/system.servicemodel.nettcpbinding.maxconnections?view=netframework-4.8

There is servicethrottling property in WCF service, which specifies the restriction mechanism of windows communication foundation (WCF) service. You can prevent excessive consumption of resources by setting serviceThrottling in the service.

The following configuration example specifies that the service limits the maximum concurrent calls to 2, and the maximum number of concurrent instances to 10.

In order to prevent excessive consumption of resources, the channel needs to be closed after each call by the client-side.

       ServiceReference1.Service1Client service1Client = new ServiceReference1.Service1Client();
        service1Client.GetData(0);
        service1Client.Close();

For more information about serviceThrottling, please refer to the following link:

https://docs.microsoft.com/zh-cn/dotnet/framework/configure-apps/file-schema/wcf/servicethrottling