TCP socket accept() returns on [SYN] on windows server 2012

Asked 7 years ago
Viewed 593 times

I use HAProxy which sends health check every 10 seconds.

It goes in the following fashion:

HAProxy -> server: [SYN]
server-> HAProxy : [SYN, ACK]
HAProxy->server  : [RST, ACK]

My TCP server is written in java in the following way:

while (true){
    Socket socket = kaServerSocket.accept();
    MyListener listener = new MyListener(socket);
    listener.start(); //costly operation

On windows 7, accept() does not return after this exchange (it returns after the regular syn->ack->syn handshake), and that's what I need.

However, when the application is running on Windows server 2012, accept() function returns on the first [SYN] which is sent from HAProxy, and performs the costly operation.

So I have 2 questions:

  1. Is this behavior configurable?

  2. If I don't want to wait for the first bit or message before I run the listener, how can I detect the connection is from HAProxy on windows 2012?


May it be connected to the ATM TCP/IP on Windows?

When using the accept function, realize that the function may return before connection establishment has traversed the entire distance between sender and receiver. This is because the accept function returns as soon as it receives a CONNECT ACK message; in ATM, a CONNECT ACK message is returned by the next switch in the path as soon as a CONNECT message is processed (rather than the CONNECT ACK being sent by the end node to which the connection is ultimately established). As such, applications should realize that if data is sent immediately following receipt of a CONNECT ACK message, data loss is possible, since the connection may not have been established all the way between sender and receiver.

asked 7 years ago

Correct Answer

See How does the socket API accept() function work?

From It seems like this is the expected behavior as HAproxy is opening the socket to the client in order to route it to the other machine.

The problem is that HAproxy is TCP compliant :)

A workaround should be to start doing your logic after some logic from the server was verified (for example, a small message was sent and an ACK was recieved though the socket).

answered 7 years ago