Varnish是一款强大的反向代理加速软件，关于其工作原理可以参考上图，其具体流程及VCL语法我这里就不做说明，网上资料多，大家还可以对照参考其和。

一、安装CentOS5.8系统环境下的依耐关系

yum install gcc gcc-c++yum install automake autoconflibtool ncurses-devel libxslt groff pcre-devel pkgconfig libtool -y

二、下载varnish-2.1.5源码包，并进行编译安装。

cd /usr/local/srcwget  http://repo.varnish-cache.org/source/varnish-2.1.5.tar.gztar zxvf varnish-2.1.5.tar.gzcd varnish-2.1.5../autogen.sh

#autogen.sh命令是用来检查软件的依耐关系是否满足，如果报错的话， 则应该如下

正常所示：

+ aclocal+ libtoolize --copy --force+ autoheader+ automake --add-missing --copy --foreign+ autoconf

继续编译安装：

./configure --prefix=/usr/local/varnish --enable-dependency-tracking --enable-debugging-symbols --enable-developer-warnings -enable-extra-warningsmake && make install && cd ../

三、创建varnish用户和组，以及varnish缓存文件和日志存放目录：

/usr/sbin/groupadd varnish/usr/sbin/useradd -s /sbin/nologin  -g varnish varnishmkdir -p /data/varnish/{cache,log}chown  -R varnish:varnish /data/varnish/{cache,log}

四、我的测试环境是两台Web机器，IP为192.168.1.103（域名为http://www.yuhongchun027.net）的varnish机器对后端IP为192.168.1.104和192.168.1.105的机器进行反向代理加速，其配置文件/usr/local/varnish/etc/varnish/better.vcl如下所示：

backend rserver1{.host ="192.168.1.104";.port = "80";.probe = {.timeout = 5s;          #等待多长时间超时.interval = 2s;          #检查时间间隔.window = 10;         #varnish将维持10个sliding windows的结果.threshold = 8;         #如果是8次.windows检查是成功的，就宣告后端的Web机器是健康的}}backend rserver2{.host ="192.168.1.105";.port = "80";.probe = {.timeout = 5s;     .interval = 2s;    .window = 10;      .threshold = 8;}}#指定一个名为realserver组，使用random机制，权重越大，分配的访问越多，可根据服务器性能来设定；而round-robin（轮询）机制是不能指定weight的director realserver random {{.backend = rserver1;.weight = 5;}{.backend = rserver2;.weight = 6;}}#定义能清理缓存的机器，这里只允许本机能用purge的方式清理acl purge { "localhost"; "127.0.0.1"; }sub vcl_recv{  if (req.http.host ~"^(.*).yuhongchun027.net")  {           set req.backend =realserver;    }        else     {             error 200 "Nocahce for this domain";       }                   if (req.request =="PURGE")         {                    if (!client.ip ~purge)             {                            error 405"Not allowed.";                      }           else             {                return (pipe);              }}#获取客户端真实IP地址if(req.http.x-forwarded-for){          set req.http.X-Forwarded-For =         req.http.X-Forwarded-For "," client.ip; }else{            set req.http.X-Forwarded-For =client.ip;        }#对HTTP协议中的GET、HEAD请求进行缓存，对POST请求透过，让其直接访问后端Web服务器。之所以这样配置，是因为POST请求一般是发送数据给服务器的，需要服务器接收、处理，所以不缓存；if (req.request !="GET" && req.request != "HEAD"){         return (pipe); } if (req.http.Expect){        return (pipe);}if (req.http.Authenticate|| req.http.Cookie){         return (pass); } if (req.http.Cache-Control~ "no-cache"){        return (pass); }#对JSP或者PHP文件不缓存if(req.url ~"\.jsp" || req.url ~ "\.php" ){         return (pass); } else{ return (lookup); }}sub vcl_pipe{return (pipe);}sub vcl_pass{return (pass);}sub vcl_hash{set req.hash += req.url;if (req.http.host){   set req.hash +=req.http.host;}else{  set req.hash +=server.ip;}  return (hash);}sub vcl_hit{if (req.request =="PURGE"){  set obj.ttl = 0s;       error 200"Purged.";}if (!obj.cacheable){   return (pass);}return (deliver);}sub vcl_miss{ if (req.request =="PURGE"){   error 404 "Not incache."; }if (req.http.user-agent ~"spider"){    error 503 "Notpresently in cache"; }     return (fetch);}sub vcl_fetch{if (req.request =="GET" && req.url ~ "\.(txt|js)$"){   set beresp.ttl = 3600s; } else{   set beresp.ttl = 30d;}if (!beresp.cacheable){   return (pass);} if (beresp.http.Set-Cookie){  return (pass);} return (deliver);}sub vcl_deliver { if (obj.hits > 0) {   set resp.http.X-Cache= "HIT  FROM www.yuhongchun027.net"; } else {   set resp.http.X-Cache= "MISS FROM www.yuhongchun027.net"; }return (deliver);}

五、启动varnish的命令很长，如下所示：

/usr/local/varnish/sbin/varnishd -n /data/varnish/cache -f /usr/local/varnish/etc/varnish/better.vcl -a 0.0.0.0:80 -sfile,/data/varnish/varnish_cache.data,8G  -p user=varnish -p group=varnish -p default_ttl=14400 -p thread_pool_max=8000 -p send_timeout=20 -w5,51200,30 -T 127.0.0.1:3500  -P /usr/local/varnish/var/varnish.pid

验证其是否生效可以用curl –I命令，如下所示：

[root@localhost cache]# curl -I http://www.yuhongchun027.net/

以下结果显示varnish缓存已经起作用了：

HTTP/1.1 200 OKServer: Apache/2.2.3 (CentOS)Last-Modified: Wed, 28 Aug 2013 16:27:33 GMTETag: "10d242-e-776b6740"Content-Type: text/html; charset=UTF-8Content-Length: 14Date: Wed, 21 Aug 2013 17:47:48 GMTX-Varnish: 1584727079 1584726982Age: 10101Via: 1.1 varnishConnection: keep-aliveX-Cache: HIT  FROM www.yuhongchun027.net

六、如果vcl配置文件发生改动，想要不重启而直接reload，可以用如下操作，可以在本机上进行telnet操作，连接3500管理端口：

telnet 127.0.0.1 3500vcl.load newconfig /usr/local/varnish/etc/varnish/better.vcl200 13 VCL compiled.vcl.use newconfig200 0

如果显示有200字样，则表示已经正常reload了，newconfig这个名字是自己定义的，熟悉varnish操作的朋友应该也清楚，通过telnet连接本机还可以进行清理缓存。

七、用varnishadm命令来清理缓存，例子如下所示：

清除所有缓存

/usr/local/varnish/bin/varnishadm -T 192.168.1.103:3500 url.purge *$

清除image目录下所有缓存

/usr/local/varnish/bin/varnishadm -T 192.168.1.103:3500 url.purge /image/

查看最近清除的详细url列表，可执行如下命令：

/usr/local/varnish/bin/varnishadm –T 192.168.1.103:3500 purge.list

另外，缓存命中率的高低直接说明了varnish的运行状态和效果，如果缓存率命中率过低，我们应该对varnish配置进行检查调整来进行提高，查看其命中率命令如下所示：

/usr/local/varnish/bin/varnishstat -n /data/varnish/cache

八、内核优化如下所示：

编辑/etc/sysctl.conf，添加如下选项：

net.ipv4.tcp_syncookies = 1net.ipv4.tcp_tw_reuse = 1net.ipv4.tcp_tw_recycle = 1net.ipv4.ip_local_port_range = 1024 65000net.ipv4.tcp_max_syn_backlog = 8192net.ipv4.tcp_max_tw_buckets = 5000net.ipv4.tcp_max_syn_backlog = 65536net.core.netdev_max_backlog =  32768net.core.somaxconn = 32768net.core.wmem_default = 8388608net.core.rmem_default = 8388608net.core.rmem_max = 16777216net.core.wmem_max = 16777216net.ipv4.tcp_timestamps = 0net.ipv4.tcp_synack_retries = 2net.ipv4.tcp_syn_retries = 2net.ipv4.tcp_tw_recycle = 1net.ipv4.tcp_tw_reuse = 1net.ipv4.tcp_mem = 94500000 915000000 927000000net.ipv4.tcp_max_orphans = 3276800

执行如下命令，让改动配置立即生效：

/sbin/sysctl –p

注意：老生常谈的ulimit的问题，这个话题说得太多了，这里实在不想再提了，记得将在/etc/rc.local添加如下内容：

ulimit –SHn 65535

注意：记得在启动varnish之前将此命令手动执行一遍（最方便的做法是放进经常运行的监控脚本或服务启动脚本），另外，在工作中发现，CentOS6.X x86_64下更改ulimit跟CentOS5.X x86_64是不同的，这点也请大家注意。以上即为varnish-2.1.5在CentOS5.8 x86_64下的安装配置过程，记录下作为工作笔记，方便以后在新机器上部署，年纪大了，起个备忘作用而矣。