backlog <conns>

Give hints to the system about the approximate listen backlog desired size

可用段落 :

参数 :

<conns> is the number of pending connections. Depending on the operating system, it may represent the number of already acknowledged connections, of non-acknowledged ones, or both.

In order to protect against SYN flood attacks, one solution is to increase the system's SYN backlog size. Depending on the system, sometimes it is just tunable via a system parameter, sometimes it is not adjustable at all, and sometimes the system relies on hints given by the application at the time of the listen() syscall. By default, HAProxy passes the frontend's maxconn value to the listen() syscall. On systems which can make use of this value, it can sometimes be useful to be able to specify a different value, hence this backlog parameter.

On Linux 2.4, the parameter is ignored by the system. On Linux 2.6, it is used as a hint and the system accepts up to the smallest greater power of two, and never more than some limits (usually 32768).

参考 : "maxconn" and the target operating system's tuning guide.