负载均衡有多种实现方法，nginx、apache、LVS、F5硬件、DNS等。

DNS的负载均衡就是一个域名指向多个ip地址，客户访问的时候进行轮询解析

操作方法，在域名服务商解析的DNS也可以是第三方DNS提供商 上添加多条A记录

qq.com DNS解析

参考：

http://blog.csdn.net/cywosp/article/details/38017027

http://www.cnblogs.com/cuihongyu3503319/archive/2012/07/09/2583129.html

dns解析的弊端：

1：无法获取解析的主机状态

2：dns一般三大运行商做了N多节点解析，修改dns后会有一定时间的延迟

Nginx的负载均衡

Nginx的负载就是多个主机之间进行负载解析

分配方式：

配置：

操作

这里我们设置的是dns解析和一台nginx的负载均衡（非两台nginx互做解析），在A主机nginx.conf之前设置不变的情况下，新增多个端口对应之前域名

我们非两台nginx互做解析是因为A配置强劲，且已经上线运行。不影响A的情况下，用B做一个当A不工作时的负载。

################  A主机原域名设置 #########################################server {listen       80 ;server_name  yiiui.com;root   "E:/www/yiiui/backend/web";location / {index  index.html index.htm index.php;#autoindex  on;if (!-e $request_filename){rewrite ^/(.*) /index.php?r=$1 last;}}location ~ \.php(.*)$ {fastcgi_pass   127.0.0.1:9000;fastcgi_index  index.php;fastcgi_split_path_info  ^((?U).+\.php)(/?.+)$;fastcgi_param  SCRIPT_FILENAME  $document_root$fastcgi_script_name;fastcgi_param  PATH_INFO  $fastcgi_path_info;fastcgi_param  PATH_TRANSLATED  $document_root$fastcgi_path_info;include        fastcgi_params;}
}server {listen       80;server_name  m.yiiui.com ;root   "E:/www/yiiui/myweb/web";location / {index  index.html index.htm index.php;#autoindex  on;if (!-e $request_filename){rewrite ^/(.*) /index.php?r=$1 last;}}location ~ \.php(.*)$ {fastcgi_pass   127.0.0.1:9001;fastcgi_index  index.php;fastcgi_split_path_info  ^((?U).+\.php)(/?.+)$;fastcgi_param  SCRIPT_FILENAME  $document_root$fastcgi_script_name;fastcgi_param  PATH_INFO  $fastcgi_path_info;fastcgi_param  PATH_TRANSLATED  $document_root$fastcgi_path_info;include        fastcgi_params;}
}################  新增 nginx负载均衡端口域名  81  82  .... #########################################server {listen       81 ;server_name  yiiui.com;root   "E:/www/yiiui/backend/web";location / {index  index.html index.htm index.php;#autoindex  on;if (!-e $request_filename){rewrite ^/(.*) /index.php?r=$1 last;}}location ~ \.php(.*)$ {fastcgi_pass   127.0.0.1:9000;fastcgi_index  index.php;fastcgi_split_path_info  ^((?U).+\.php)(/?.+)$;fastcgi_param  SCRIPT_FILENAME  $document_root$fastcgi_script_name;fastcgi_param  PATH_INFO  $fastcgi_path_info;fastcgi_param  PATH_TRANSLATED  $document_root$fastcgi_path_info;include        fastcgi_params;}
}server {listen       82;server_name  m.yiiui.com ;root   "E:/www/yiiui/myweb/web";location / {index  index.html index.htm index.php;#autoindex  on;if (!-e $request_filename){rewrite ^/(.*) /index.php?r=$1 last;}}location ~ \.php(.*)$ {fastcgi_pass   127.0.0.1:9001;fastcgi_index  index.php;fastcgi_split_path_info  ^((?U).+\.php)(/?.+)$;fastcgi_param  SCRIPT_FILENAME  $document_root$fastcgi_script_name;fastcgi_param  PATH_INFO  $fastcgi_path_info;fastcgi_param  PATH_TRANSLATED  $document_root$fastcgi_path_info;include        fastcgi_params;}
}

B主机的nginx.conf中新增同A主机一样的带端口设置 （如果为内网局域网先设置hosts）

server {listen       81;server_name  yiiui.com;root   "C:/www/yiiui/backend/web";location / {index  index.html index.htm index.php;#autoindex  on;if (!-e $request_filename){rewrite ^/(.*) /index.php?r=$1 last;}}location ~ \.php(.*)$ {fastcgi_pass   127.0.0.1:9000;fastcgi_index  index.php;fastcgi_split_path_info  ^((?U).+\.php)(/?.+)$;fastcgi_param  SCRIPT_FILENAME  $document_root$fastcgi_script_name;fastcgi_param  PATH_INFO  $fastcgi_path_info;fastcgi_param  PATH_TRANSLATED  $document_root$fastcgi_path_info;include        fastcgi_params;}
}server {listen       82;server_name  m.yiiui.com;root   "C:/www/yiiui/myweb/web";location / {index  index.html index.htm index.php;#autoindex  on;if (!-e $request_filename){rewrite ^/(.*) /index.php?r=$1 last;}}location ~ \.php(.*)$ {fastcgi_pass   127.0.0.1:9000;fastcgi_index  index.php;fastcgi_split_path_info  ^((?U).+\.php)(/?.+)$;fastcgi_param  SCRIPT_FILENAME  $document_root$fastcgi_script_name;fastcgi_param  PATH_INFO  $fastcgi_path_info;fastcgi_param  PATH_TRANSLATED  $document_root$fastcgi_path_info;include        fastcgi_params;}
}

设置B主机的负载域名：

upstream yiiui.com{server 127.0.0.1:81;  #这里是你自己要做负载均衡的服务器地址1    # 本地windows可以，外网linux 要用局域网的IPserver 192.168.2.101:81; #这里是要参与负载均衡的地址2
}upstream m.yiiui.com{server 127.0.0.1:82 weight=200;  #这里是你自己要做负载均衡的服务器地址1server 192.168.2.101:82 weight=2; #这里是要参与负载均衡的地址2
}server {listen       80;server_name  yiiui.com;     #设置所有web服务器负载的共同域名 location / {proxy_pass http://yiiui.com;  #确定需要代理的URL，端口或socket。 proxy_set_header Host   $host;}
}server {listen       80;server_name  m.yiiui.com;     #设置所有web服务器负载的共同域名 location / {proxy_pass http://m.yiiui.com;  #确定需要代理的URL，端口或socket。 proxy_set_header Host   $host;}
}

参考:

http://www.cnblogs.com/xiaogangqq123/archive/2011/03/04/1971002.html

http://825536458.blog.51cto.com/4417836/1784794

http://baidutech.blog.51cto.com/4114344/1033718/

设置nginx的负载均衡后的session同步登录状态问题

必须要将A、B主机的session指向一个地方才能使访问的域名当前登录的状态一致。可以使用mysql、memcache进行会话存储

windows的memcached 同时运行局域网ip访问

Yii2 的设置：

# 设置session保存在mysql中'session' => ['class' => 'yii\web\DbSession',// Set the following if you want to use DB component other than// default 'db'.// 'db' => 'mydb',// To override default session table, set the following// 'sessionTable' => 'my_session',],

参考：

http://wiki.jikexueyuan.com/project/yii-2.0-guide/tutorial-performance-tuning.html

http://blog.sina.com.cn/s/blog_8a18c33d01013rp9.html

注：memcache存储会话时，重启、重启操作系统会导致全部数据消失。内容容量达到指定值之后，就基于LRU(Least Recently Used)算法自动删除不使用的缓存。