A Nginx module make nginx in self-defence according to the values in shared memory. A external script can periodically change the values in shared memory according to the gathered information of the server machine, such as free memory, load average, swap ratio, bandwidth and so on. ngx_http_self_defence will make internal redirect according to the value and matched action in config.

http {
    defence_shm      12345 10;

    server {
        listen       80  default deferred;
        server_name  localhost;

        defence_at       1;
        defence_action   1  90% @internal;
        defence_action   2  80% /defence;

        location @internal {
            return 500;
        }

        location /defence {
            return 503;
        }

        location / {
            root   html;
            index  index.html index.htm;
        }
    }
}

• syntax : defence_shm shm_key [shm_length]
• default: --
• context: http

Set SYSV shared memory key and length used in defence module. The shm_length must between 0(excluding) and 255(including). If no 'shm_length' supplied, use 8 as default;

• syntax : defence_at pos
• default: defence_at 0
• context: http, server, location

Specify the offset in shared memory of the byte whose value the module will detect to trigger the action handler specified in defence_action. 'pos' should be between 0(excluding) and 255(including).

• syntax : defence_action value [ratio% [action]]
• default: --
• context: http, server, location

Specify the value of shared memory. When matched with 'value' parameter, the request will be redirected to the URL specified by the 'action' parameter. Nginx will return 503 if no 'action' URL provided.

If no 'ratio' specified, all request will trigger the action. Otherwise, only ratio percentage will trigger the action. The 'ratio' must be between 0 and 100.

A external script should periodically update the value in shared memory, then the Nginx can make it in self-defence according the values.

This module is only tested on Linux machine.

FengGu [email protected]