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nginx的geo模块可以做全局负载均衡，可以要根据客户端ip访问到不同的server。比如，可以将电信的用户访问定向到电信服务器，网通的用户重定向到网通服务器。
我这里实现只有移动手机用户才能访问服务器。首先要收集全移动网关ip.
配置如下：

worker_processes 1;
events {
        worker_connections 1024;
}

http {
        include         mime.types;
        default_type    application/octet-stream;
        sendfile        on;
        keepalive_timeout 65;
        geo $cmccip {
                default 1;　　　#　未定义ip的值为1
                include cmcc.conf; 加载geo.conf文件，这个文件定义移动网关ip
        }
        server {
                listen 801;
                server_name XXXXX;
                location / {
                        if ($cmccip) {
                                rewrite ^ http://tx.com.cn;   未定义ip即非移动ip重定向到tx.com.cn;
                        }
                        root /data/www;
                        index index.wml index.html;

                }
        }
}

cmcc.conf文件内容如下：
211.136.222.90/32 0;

测试环境：

CPU：Xeon2.8G X2 
RAM：4G
OS：RedHat As5.3 X64

工具：apache ab
参数：ab -i -c 500 -n 100000

最终服务端：2个squid 需实现均衡负载

成绩如下：

####### Nginx + haproxy :  (由Nginx通过反向代理发送请求至haproxy, 并由其进行均衡负载)

Concurrency Level:      500
Time taken for tests:   53.758 seconds
Complete requests:      100000
Failed requests:        0
Write errors:           0
Total transferred:      38600386 bytes
HTML transferred:       0 bytes
Requests per second:    1860.19 [#/sec] (mean)
Time per request:       268.790 [ms] (mean)
Time per request:       0.538 [ms] (mean, across all concurrent requests)
Transfer rate:          701.21 [Kbytes/sec] received

####### haproxy :  (单独由haproxy进行均衡负载)

Concurrency Level:      500
Time taken for tests:   32.562 seconds
Complete requests:      100000
Failed requests:        0
Write errors:           0
Total transferred:      36606588 bytes
HTML transferred:       0 bytes
Requests per second:    3071.02 [#/sec] (mean)
Time per request:       162.812 [ms] (mean)
Time per request:       0.326 [ms] (mean, across all concurrent requests)
Transfer rate:          1097.85 [Kbytes/sec] received

####### nginx : (单独由nginx进行均衡负载)

Concurrency Level:      500
Time taken for tests:   36.539 seconds
Complete requests:      100000
Failed requests:        0
Write errors:           0
Total transferred:      38600000 bytes
HTML transferred:       0 bytes
Requests per second:    2736.82 [#/sec] (mean)
Time per request:       182.694 [ms] (mean)
Time per request:       0.365 [ms] (mean, across all concurrent requests)
Transfer rate:          1031.65 [Kbytes/sec] received

反复测试，得出其结果：

Haproxy 单独进行均衡负载的性能最强，超过了Nginx。
然而 Nginx + Haproxy 的搭配性能最弱，应该是跟通过了2层反向代理有关。

所以想用 Haproxy 替代 Nginx 所自带的均衡负载功能将会令性能打折。
但 Nginx 的配置法则确远比 Haproxy 灵活。

还是视乎用途而决定吧。