Is there a way to specify which NIC the traffic goes?

[rodolfo-sousa]

Is there a way to specify which network card the traffic of a specific route goes?
Something like this:

            var handler = new SocketsHttpHandler
            {
                // Set the specific local IP address to bind to a NIC
                LocalEndPoint = new IPEndPoint(IPAddress.Parse("YOUR_NIC_IP_ADDRESS"), 0), 
            };

[MihaZupan]

You can customize how the socket is created by setting the SocketsHttpHandler.ConnectCallback, presumably calling Bind there should work.
For reference the default implementation is

Socket socket = new Socket(SocketType.Stream, ProtocolType.Tcp) { NoDelay = true };
try
{
    // Bind here
    await socket.ConnectAsync(endPoint, cancellationToken);
    return new NetworkStream(socket, ownsSocket: true);
}
catch
{
    socket.Dispose();
    throw;
}

[rodolfo-sousa]

You can customize how the socket is created by setting the SocketsHttpHandler.ConnectCallback, presumably calling Bind there should work. For reference the default implementation is

Socket socket = new Socket(SocketType.Stream, ProtocolType.Tcp) { NoDelay = true };
try
{
    // Bind here
    await socket.ConnectAsync(endPoint, cancellationToken);
    return new NetworkStream(socket, ownsSocket: true);
}
catch
{
    socket.Dispose();
    throw;
}

Thank you for your suggestion, so could be something like this:

public class CustomHttpClientFactory(ILogger<CustomHttpClientFactory> logger) : IForwarderHttpClientFactory
{
    private readonly ILogger<CustomHttpClientFactory> _logger = logger;

    public HttpMessageInvoker CreateClient(ForwarderHttpClientContext context)
    {
        var handler = new SocketsHttpHandler
        {
            // Other HttpClient handler configurations as needed
            ConnectCallback = async (context, cancellationToken) =>
            {
                Socket socket = new(SocketType.Stream, ProtocolType.Tcp) { NoDelay = true };
                try
                {
                    // Bind here
                    await socket.ConnectAsync(new IPEndPoint(IPAddress.Parse("YOUR_NIC_IP_ADDRESS"), 0), cancellationToken);
                    return new NetworkStream(socket, ownsSocket: true);
                }
                catch
                {
                    socket.Dispose();
                    throw;
                }
            }
        };

        return new HttpMessageInvoker(handler, disposeHandler: true);
    }
}

and there is a way to specify only for a specific route and not all routes configured?

[MihaZupan]

You should inherit from ForwarderHttpClientFactory instead of the interface and just extend the ConfigureHandler virtual method. That will reuse clients between cluser updates for you, honor other client configuration, and set reasonable defaults.

Each cluster has a separate client, so you can change behavior based on the ForwarderHttpClientContext that's passed in.

await socket.ConnectAsync(new IPEndPoint(IPAddress.Parse("YOUR_NIC_IP_ADDRESS"), 0)

No. You're still connecting the the remote endpoint, you just want to socket.Bind(nic) before that.

[rodolfo-sousa]

Something like this? Should ConnectAsync have the same IP of the NIC that handle the traffic?

public class CustomHttpClientFactory(ILogger<CustomHttpClientFactory> logger) : ForwarderHttpClientFactory
{
    private readonly ILogger<CustomHttpClientFactory> _logger = logger;

        protected override void ConfigureHandler(ForwarderHttpClientContext context, SocketsHttpHandler handler)
    {
        base.ConfigureHandler(context, handler);
        //Only a specific cluster needs to bind to a specific NIC
        if (context.ClusterId == "cluster1")
        {
            handler.ConnectCallback = async (context, cancellationToken) =>
            {
                Socket socket = new(SocketType.Stream, ProtocolType.Tcp) { NoDelay = true };
                try
                {
                    // IPAddress to bind to a specific NIC
                    socket.Bind(new IPEndPoint(IPAddress.Parse("YOUR_NIC_IP_ADDRESS"), 0));
                    // Connect here
                    await socket.ConnectAsync(new IPEndPoint(IPAddress.Parse("YOUR_NIC_IP_ADDRESS"), 0), cancellationToken);
                    return new NetworkStream(socket, ownsSocket: true);
                }
                catch
                {
                    socket.Dispose();
                    throw;
                }
            };
        }
    }
}

[MihaZupan]

Connect takes the address of the endpoint you actually want to connect to, i.e. your backend server, so you should pass it the context.DnsEndPoint.
That's the destination you specified in the cluster config.

Otherwise that seems right.