网站接入百度云加速后，nginx的访问日志里面多了很多云加速节点来探测网站是否存活的记录：

42.236.7.68 - - [30/May/2017:08:36:59 +0800] "HEAD / HTTP/1.1" 200 0 "-" "Baidu-YunJiaSu-Bot(su.baidu.com)"
42.236.7.68 - - [30/May/2017:08:36:59 +0800] "HEAD / HTTP/1.1" 200 0 "-" "Baidu-YunJiaSu-Bot(su.baidu.com)"
122.246.5.11 - - [30/May/2017:08:37:52 +0800] "HEAD / HTTP/1.1" 200 0 "-" "Baidu-YunJiaSu-Bot(su.baidu.com)"
117.34.28.13 - - [30/May/2017:08:37:52 +0800] "HEAD / HTTP/1.1" 200 0 "-" "Baidu-YunJiaSu-Bot(su.baidu.com)"
119.188.132.10 - - [30/May/2017:08:37:52 +0800] "HEAD / HTTP/1.1" 200 0 "-" "Baidu-YunJiaSu-Bot(su.baidu.com)"
124.95.168.140 - - [30/May/2017:08:37:52 +0800] "HEAD / HTTP/1.1" 200 0 "-" "Baidu-YunJiaSu-Bot(su.baidu.com)"
61.182.137.6 - - [30/May/2017:08:37:52 +0800] "HEAD / HTTP/1.1" 200 0 "-" "Baidu-YunJiaSu-Bot(su.baidu.com)"
122.246.5.11 - - [30/May/2017:08:37:53 +0800] "HEAD / HTTP/1.1" 200 0 "-" "Baidu-YunJiaSu-Bot(su.baidu.com)"
119.188.132.10 - - [30/May/2017:08:37:53 +0800] "HEAD / HTTP/1.1" 200 0 "-" "Baidu-YunJiaSu-Bot(su.baidu.com)"
117.34.28.13 - - [30/May/2017:08:37:53 +0800] "HEAD / HTTP/1.1" 200 0 "-" "Baidu-YunJiaSu-Bot(su.baidu.com)"
61.182.137.6 - - [30/May/2017:08:37:53 +0800] "HEAD / HTTP/1.1" 200 0 "-" "Baidu-YunJiaSu-Bot(su.baidu.com)"
124.95.168.140 - - [30/May/2017:08:37:53 +0800] "HEAD / HTTP/1.1" 200 0 "-" "Baidu-YunJiaSu-Bot(su.baidu.com)"

[root@dish log]# grep -c YunJiaSu  20170529_wordpress.log
4131
[root@dish log]# grep -c YunJiaSu  20170528_wordpress.log
4068
[root@dish log]# grep -c YunJiaSu  20170527_wordpress.log
3744

显然这些记录是无意义的，我们要让nginx写日志的时候，自动排除这些云加速的HEAD请求。
网上搜到的方法经过测试后无效，不知道是不是我姿势不对：

if ($request_method = "HEAD" ) {
 access_log off;
}

ngx_log_if模块

ngx_log_if模块是一个nginx的第三方模块，这个模块能很好的实现日志过滤功能。
下载 ngx_log_if 模块

cd /root/download
wget https://github.com/cfsego/ngx_log_if/archive/master.zip
unzip master.zip

nginx添加第三方模块

1、查看ngixn版本极其编译参数

/usr/local/nginx/sbin/nginx -V

2、进入nginx源码目录

cd nginx-1.4.4

3、以下是重新编译的代码和模块

./configure --user=www --group=www --prefix=/usr/local/nginx --without-http-cache --with-http_ssl_module --with-http_gzip_static_module --with-http_realip_module --add-module=/root/download/ngx_log_if-master

make 千万别make install，否则就覆盖安装了

make完之后在objs目录下就多了个nginx，这个就是新版本的程序了

4、备份旧的nginx程序

/usr/local/nginx/sbin/nginx -s stop
cp /usr/local/nginx/sbin/nginx{,.bak}

5、把新的nginx程序覆盖旧的
cp objs/nginx /usr/local/nginx/sbin/nginx

通过ngx_log_if进行nginx日志过滤

server {
	access_log_bypass_if ($http_user_agent ~* 'Baidu-YunJiaSu-Bot' ); 
        ## Your website name goes here.
        server_name hqidi.com www.hqidi.com;

若这个access_log_bypass_if语句加在location标签下无效的话，就把该语句加在server标签下，我就刚好遇到此问题。

ngx_log_if常用例子

server {
    # 不记录204响应状态的access日志
    access_log_bypass_if ($status = 204);
    
    # 不记录200响应状态且uri为 status.nginx 的访问日志
    access_log_bypass_if ($uri = 'status.nginx') and;
    access_log_bypass_if ($status = 200);

    # 不记录HEAD请求的日志
    access_log_bypass_if ($request = 'HEAD');

}