Discuss anti-crawler and anti-DDoS attack strategies for Nginx servers

Nginx server is a high-performance web server and reverse proxy server with powerful anti-crawler and anti-DDoS attack capabilities. This article will discuss the anti-crawler and anti-DDoS attack strategies of Nginx server and give relevant code examples.

1. Anti-crawler strategy

A crawler is an automated program used to collect data on specific websites from the Internet. Some crawler programs will put a huge burden on the website and seriously affect the normal operation of the website. Nginx can prevent malicious behavior of crawlers through the following strategies:

1. User-Agent filtering
   Crawler programs usually use specific User-Agent strings to identify themselves. By adding the following code to the Nginx configuration file, you can prohibit access to certain User-Agents:

if ($http_user_agent ~* (Baiduspider|Googlebot|Yandex)) {
    return 403;
}

The above code will prohibit access to Baidu spiders, Google crawlers and Yandex crawlers.

2. IP access frequency limit
   By setting the ngx_http_limit_req_module module of Nginx, you can limit the access frequency of IP addresses. The following is a code example:

http {
    limit_req_zone $binary_remote_addr zone=one:10m rate=100r/m;

    server {
        location / {
            limit_req zone=one burst=20 nodelay;

            ...
        }
    }
}

The above code will limit each IP address to a maximum of 100 accesses per minute. Requests exceeding the limit will be delayed or rejected.

2. Anti-DDoS attack strategy

Distributed denial of service (DDoS) attacks overload the target server through a large amount of malicious traffic. Nginx can adopt the following strategies to resist DDoS attacks:

1. Connection limit
   Set the ngx_http_limit_conn_module module of Nginx to limit the number of simultaneous connections for each IP address. The following is a code example:

http {
    limit_conn_zone $binary_remote_addr zone=concurrent:10m;

    server {
        location / {
            limit_conn concurrent 50;

            ...
        }
    }
}

The above code will limit each IP address to a maximum of 50 simultaneous connections.

2. Request length limit
   By setting Nginx's client_body_buffer_size and client_max_body_size parameters, you can limit the length of the request to prevent malicious requests from causing server overflow. The following is a code example:

http {
    client_body_buffer_size 10K;
    client_max_body_size 10m;

    server {
        location / {
            ...
        }
    }
}

The above code will limit the requested size to no more than 10MB.

To sum up, Nginx server has powerful anti-crawler and anti-DDoS attack capabilities. Through policies such as User-Agent filtering, IP access frequency limit, connection number limit, and request length limit, the server can be effectively protected from crawlers and DDoS attacks.

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