如何阻止nginx记录Amazon Route 53运行状况检查请求？

目前,我的AWS运行状况检查正在无情地击中我的服务器:

...
54.228.16.40 - - [14/Jan/2014:10:17:22 +0000] "GET / HTTP/1.1" 301 178 "-" "Amazon Route 53 Health Check Service"
54.248.220.40 - - [14/Jan/2014:10:17:24 +0000] "GET / HTTP/1.1" 301 178 "-" "Amazon Route 53 Health Check Service"
54.232.40.110 - - [14/Jan/2014:10:17:25 +0000] "GET / HTTP/1.1" 301 178 "-" "Amazon Route 53 Health Check Service"
54.241.32.78 - - [14/Jan/2014:10:17:26 +0000] "GET / HTTP/1.1" 301 178 "-" "Amazon Route 53 Health Check Service"
54.245.168.46 - - [14/Jan/2014:10:17:28 +0000] "GET / HTTP/1.1" 301 178 "-" "Amazon Route 53 Health Check Service"
54.251.31.174 - - [14/Jan/2014:10:17:28 +0000] "GET / HTTP/1.1" 301 178 "-" "Amazon Route 53 Health Check Service"
...

我想将NginX配置为不使用用户代理记录任何请求"Amazon Route 53 Health Check Service".

我目前的尝试如下:

# default server for forwarding all requests over to main www domain
server {
    listen 80 default_server;

    server_name _;

    return 301 $scheme://www.example.com$request_uri;
}

# server configured to catch aws health check requests
server {
    listen 80;
    server_name 12.345.67.89;

    location / {
        if ( $http_user_agent ~* 'Amazon Route 53 Health Check Service' ) {
            access_log off;
            return 200 'Service OK';      
        }
    }
}

# actual application server
server {
    listen 80;
    server_name www.example.com;

    location / { 
        ...
    }
}

这看起来对我来说很好,事实上当我将CURL设置为健康检查设置为匹配的相同地址时:

curl --user-agent "Amazon Route 53 Health Check Service" http://12.345.67.89:80/

我得到了我所期望的:

Service OK

我的请求不会在日志中结束.

但是,当这些请求来自实际的AWS运行状况检查时,我的日志会继续被这些请求所淹没.

关于我在哪里做错的任何想法？

谢谢