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前言

CDN（Content Delivery Network），即内容分发网络。通过中心平台的负载均衡、内容分发、调度等功能模块，使用户快速就近获取所需内容，提高访问命中率。

CDN关键技术：
1.缓存
2.分发能力
3.负载均衡

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一、CDN安装以及负载均衡

准备：

三台虚拟机一台server1作为CDN服务的主机，其余两台server2、3为后端接收负载均衡的主机。
varnish安装包及相关依赖包。

server1

安装varnish

yum install -y jemalloc-3.6.0-1.el7.x86_64.rpm jemalloc-devel-3.6.0-1.el7.x86_64.rpm varnish-4.0.5-1.el7.x86_64.rpm varnish-libs-4.0.5-1.el7.x86_64.rpm

配置文件修改

可以修改内核文件数

sysctl -a|grep file

vim /etc/security/limits.conf

vim /etc/varnish/default.vcl

#
# This is an example VCL file for Varnish.
#
# It does not do anything by default, delegating control to the
# builtin VCL. The builtin VCL is called when there is no explicit
# return statement.
#
# See the VCL chapters in the Users Guide at https://www.varnish-cache.org/docs/
# and http://varnish-cache.org/trac/wiki/VCLExamples for more examples.

# Marker to tell the VCL compiler that this VCL has been adapted to the
# new 4.0 format.
vcl 4.0;

# Default backend definition. Set this to point to your content server.
# 定义web1访问172.25.9.2的80端口，web2为访问172.25.9.3的80端口
backend web1 {
    .host = "172.25.9.2";
    .port = "80";
}

backend web2 {
    .host = "172.25.9.3";
    .port = "80";
}
#负载均衡，当访问域名为www.westos.org/westos.org 访问web1；当访问域名为bbs.westos.org访问web2；其余返回404
sub vcl_recv {
if (req.http.host ~ "^(www.)?westos.org") {
                set req.http.host = "www.westos.org";
                set req.backend_hint = web1;
                #return(pass);
        }
        elseif (req.http.host ~ "^bbs.westos.org") {
                set req.backend_hint = web2;
                #return(pass);
        }
        else {
                return(synth(404,"Not in cache"));
        }

    # Happens before we check if we have this in cache already.
    #
    # Typically you clean up the request here, removing cookies you don't need,
    # rewriting the request, etc.
}

sub vcl_backend_response {
    # Happens after we have read the response headers from the backend.
    #
    # Here you clean the response headers, removing silly Set-Cookie headers
    # and other mistakes your backend does.
}
# 如果命中，显示HIT from westos cache；否则显示MISS from westos cache
sub vcl_deliver {
    if (obj.hits > 0) {
        set resp.http.X-Cache = "HIT from westos cache";
        }
        else {
        set resp.http.X-Cache = "MISS from westos cache";
        }
        return (deliver);
}

    # Happens when we have all the pieces we need, and are about to send the
    # response to the client.
    #
    # You can do accounting or modifying the final object here.

vim varnish.params
设定监听端口为80

VARNISH_LISTEN_PORT=80

开启服务

systemctl start varnish.service

server2\3
后端主机安装并打开apache服务即可

yum install -y httpd
echo 'www.westos.org' > /var/www/html/index.html
systemctl start httpd

测试机（访问的主机）解析：

访问结果：

二、CDN + Nginx负载均衡

重新打开全新的虚拟机server4配置nginx

server4

详细源码编译步骤可参考本人之前的博客：
企业运维实战LAMP架构–nginx、php、mysql源码编译安装及结合phpmyadmin使用

解压tar包并进入解压后目录

tar zxf nginx-1.20.1.tar.gz
ls
cd nginx-1.20.1/

安装依赖性

yum install -y gcc
yum install -y pcre-devel
yum install -y openssl-devel

编译

./configure --help
./configure --with-http_ssl_module

安装

make install

制作软链接

ln -s /usr/local/nginx/sbin/nginx /usr/local/bin/

检测软链接

nginx -t

编辑nginx配置文件进行负载均衡

vim /usr/local/nginx/conf/nginx.conf

#upstream 负载均衡器
upstream westos {
    server 172.25.9.2:80;
    server 172.25.9.3:80;
    }


...
# proxy_pass 反向代理器
server {
        listen 80;
        server_name www.westos.org;

        location / {
        proxy_pass http://westos;
}


}

检测语法，开启nginx服务

nginx -t
nginx

server1 将cdn与nginx连接完成负载均衡

vim default.vcl

# 添加web3
backend web3 {
    .host = "172.25.9.4";
    .port = "80";
}

...
# 访问域名www.westos.org，代理到web3
sub vcl_recv {
if (req.http.host ~ "^(www.)?westos.org") {
                set req.http.host = "www.westos.org";
                set req.backend_hint = web3;
                return(pass);
        }
        elseif (req.http.host ~ "^bbs.westos.org") {
                set req.backend_hint = web2;
                #return(pass);
        }
        else {
                return(synth(404,"Not in cache"));
        }

    # Happens before we check if we have this in cache already.
    #
    # Typically you clean up the request here, removing cookies you don't need,
    # rewriting the request, etc.
}

平滑刷新varnish

systemctl reload varnish.service

测试：

curl www.westos.org 访问多次

查看后端httpd服务日志 server2、3

cat /var/log/httpd/access_log

172.25.9.4 - - [13/Jul/2021:11:26:22 +0800] "GET / HTTP/1.0" 200 25 "-" "curl/7.61.1"
172.25.9.4 - - [13/Jul/2021:11:26:23 +0800] "GET / HTTP/1.0" 200 25 "-" "curl/7.61.1"

日志查看得，访问来源于nginx。

CDN对后端进行健康检查

probe backend_healthcheck {
    .url = "/index.html";
    .window = 3;
    .threshold = 2;
    .interval = 3s;
}
backend web1 {
    .host = "172.25.9.2";
    .port = "80";
    .probe = backend_healthcheck;
}
backend web2 {
    .host = "172.25.9.3";
    .port = "80";
    .probe = backend_healthcheck;
}

访问nginx显示实际访问ip

架构cdn + nginx（1） +nginx（2）

nginx默认访问地址查看

cat /usr/local/nginx/logs/access.log

nginx（1）配置 server4

只留一个后端服务器 指向后端nginx，其余注释掉

nginx（2） server3 关闭apache服务，源码编译安装nginx，并导入real ip模块

安装real ip模块

./configure --with-http_realip_module --with-http_ssl_module

make install
ln -s /usr/local/nginx/sbin/nginx /usr/local/bin/

添加real ip模块

vim /usr/local/nginx/conf/nginx.conf

 46             real_ip_header    X-Forwarded-For;
 47             real_ip_recursive on;
 48             set_real_ip_from 172.25.9.0/24;

开启服务并刷新修改

nginx

nginx -s reload

测试机访问几次，查看nginx日志

cat /usr/local/nginx/logs/access.log

访问来源于真实访问ip。