详解：nginx手机用户访问自适应页面

1. 当后端服务器出现异常，响应码为500 501 502 503 504，请求转发到静态降级服务器，从而保证业务不至于完全无法访问，对于浏览型且实时性要求不高的站点非常有用。

app_servers：应用服务器，提供正常服务页面

shopwebstatic：静态服务器，提供定时爬取的静态页面

2.请求重试：

proxy_next_upstream http_500 http_502 http_504 error timeout invalid_header;

3.根据user agent,cookie特定字段，将来源为PC版用户的请求转发到手机版页面或者恢复访问PC版本页面。

默认手机用户访问站点会跳转到手机版本，跳转判断依据是user agent，当用户点击访问电脑版本的时候，除了要判断用户的user agent外还需要判断用户的访问模式，通过cookie中特定字段的值来判断用户访问请求是到手机版本还是到PC版本。

mode=pc，mode标记用户的访问模式是PC版本，通过此cookie字段，可判断是否将user agent匹配智能手机字段的用户的请求转发到手机版本。

limit_conn_zone $server_name zone=limit:10m;
upstream app_servers {
server app_server01_ip:80 weight=1 max_fails=2;
server app_server01_ip:80 weight=1 max_fails=2 backup;
}
upstream shopwebstatic {
server shopwebstatic_server01_ip:80 weight=5;
server shopwebstatic_server02_ip:80 weight=5;
}

server {
listen 80;
server_name qunying.liu.dianping.com;
# config_apps_begin
root /data/webapps/shops-web/shared/webroot;
access_log logs/shops-web.access.log main;
error_log logs/shops-web.error.log notice;
# config_apps_end
limit_conn limit 280;
proxy_next_upstream http_500 http_502 http_504 error timeout invalid_header;

location / {

proxy_intercept_errors on;
location ~* ^/shop/(/d+)/menu{
set $mobile 0;
set $shopid $1;
set $hostid 0;
if ( $http_user_agent ~* "(Android|iPhone|Windows Phone)" ){
set $mobile "${mobile}1";
}
if ( $host ~* "m/.dianping/.com" ){
set $hostid "${hostid}1";
}

if ( $http_cookie !~* "mode=pc"){
set $mobile "${mobile}1";
}

if ( $hostid = "01" ){
proxy_pass http://app_servers/shop/$shopid/mobilemenu;
break;
}
if ( $mobile = "011" ){
rewrite ^/(.*)$ http://mobile-servers/\ redirect;
break;
}
proxy_pass http://app_servers;
break;
}
location ~* ^/shop/(/d+)/dish-(.*){
set $mobile 0;
set $shopid $1;
set $dishurl $2;
if ( $http_user_agent ~* "(Android|iPhone|Windows Phone)" ){
set $mobile "${mobile}1";
}
if ( $http_cookie !~* "mode=pc"){
set $mobile "${mobile}1";
}

if ( $mobile = "011" ){
rewrite ^/(.*)$ http://mobile-servers/shop/$shopid/product-$dishurl redirect;
break;
}
proxy_pass http://app_servers;
break;
}
location ~* ^/map/shop/(/d+)$ {
set $shopid $1;
rewrite ^/(.*)$ http://www.servers/shop/$shopid/map permanent;
proxy_set_header Host "www.servers";
break;
}
location ~* ^/shop/(/d+)(/map|/)?$ {
set $mobile 0;
if ( $http_user_agent ~* "(Android|iPhone|Windows Phone)" ){
set $mobile "${mobile}1";
}
if ( $http_cookie !~* "mode=pc"){
set $mobile "${mobile}1";
}

if ( $mobile = "011" ){
rewrite ^/(.*)$ http://mobile-servers/\ redirect;
break;
}
proxy_pass http://app_servers;
break;
}
# appserverfavcion
location ~* ^.*/favicon.ico$ {
root /data/webapps;
expires 30d;
break;
}
if ( !-f $request_filename ) {
proxy_pass http://app_servers;
break;
}
}
error_page 500 501 502 503 504 @shopstatic;
location @shopstatic {
access_log logs/shops-static-web.access.log retry;
proxy_pass http://shopwebstatic;
}

发现过去配置的规则中，由于未判断访问的主机名导致当一个应用同时被配置在pc和手机域名下，当访问pc版本域名跳转手机版本时会产生死循环重定向，如www（手机访问时）—-自动跳转到m域名—m域名解析到应用会再根据user agent和cookie规则跳转一次m域名，然后陷入死循环。

在做域名跳转的时候，最好对域名做一个判断。

location ~* /mylist/{
set $mobile 0;
if ( $http_user_agent ~* "(Android|iPhone|Windows Phone|UC|Kindle)" ){
set $mobile "${mobile}1";
}
if ( $http_host !~ "m.dianping.com" ){
set $mobile "${mobile}2";
}
if ( $cookie_vmod !~ "pc" ){
set $mobile "${mobile}3";
}
if ( $mobile = "0123" ){
rewrite ^/(.*)$ http://m.dianping.com/\ last;
break;
}
proxy_pass http://jboss8080;
break;
}