高可用解决方案 Keepalived 案例(keepalived + nginx)

案例

Nginx + Keepalived 案例

使用 Nginx + Keepalived 实现一个 web 服务高可用方案

架构图如下:

高可用解决方案 Keepalived 案例(keepalived + nginx)_第1张图片


Nginx 的安装与配置

  1. 安装软件

    # 安装nginx以及拓展源
    yum install epel-release -y
    yum install -y nginx
    
  2. Nginx 配置 web 站点

    #web1
    [root@nginx1 ~]# vi /etc/nginx/conf.d/web.conf 
    server{
        listen 8080;
        root         /usr/share/nginx/html;
        index test.html;
    }
    
    [root@nginx1 ~]# echo "

    This is web1

    " > /usr/share/nginx/html/test.html
    #web2
    [root@nginx2 ~]# vi /etc/nginx/conf.d/web.conf 
    server{
        listen 8080;
        root         /usr/share/nginx/html;
        index test.html;
    }
    
    [root@nginx2 ~]# echo "

    This is web2

    " > /usr/share/nginx/html/test.html
  3. 启动 Nginx

    nginx -t
    nginx
    

Keepalived 的安装与配置

  1. 安装 Keepalived

    yum install -y keepalived
    
  2. 配置 Keepalived(不同角色有些选项不一样:state 和 priority 配置项)

    web1:master

    vi /etc/keepalived/keepalived.conf
    
    ! Configuration File for keepalived
    global_defs {
       router_id LVS_DEVEL_1
    }
    vrrp_script nginx_check {
      script "/tools/nginx_check.sh"
      interval 1
    }
    vrrp_instance VI_1 {
      state MASTER
      #nopreempt
      interface ens33
      virtual_router_id 52
      priority 100
      advert_int 1
      authentication {
        auth_type PASS
        auth_pass test
      }
      virtual_ipaddress {
        192.168.149.100
      }
      track_script {
        nginx_check
      }
      notify_master /tools/master.sh
      notify_backup /tools/backup.sh
      notify_fault /tools/fault.sh
      notify_stop /tools/stop.sh
    }
    

    web2:slave

    vi /etc/keepalived/keepalived.conf
    
    ! Configuration File for keepalived
    global_defs {
       router_id LVS_DEVEL_2
    }
    vrrp_script nginx_check {
      script "/tools/nginx_check.sh"
      interval 1
    }
    vrrp_instance VI_1 {
      state BACKUP
      #nopreempt
      interface ens33
      virtual_router_id 52
      priority 90
      advert_int 1
      authentication {
        auth_type PASS
        auth_pass test
      }
      virtual_ipaddress {
        192.168.149.100
      }
      track_script {
        nginx_check
      }
      notify_master /tools/master.sh
      notify_backup /tools/backup.sh
      notify_fault /tools/fault.sh
      notify_stop /tools/stop.sh
    }
    
  3. 编写相关脚本

    编写 Keepalived 日志脚本(将每次工作过程输出到日志上)

    # 将所有脚本放在同一个目录下,方便集中管理
    mkdir /tools && cd /tools
    
    cat > master.sh << 'EOF'
    ip=$(hostname -I | awk '{print $1}')
    dt=$(date +'%Y%m%d %H:%M:%S')
    echo "$0--${ip}--${dt}" >> /tmp/kp.log
    EOF
    
    cat > backup.sh << 'EOF'
    ip=$(hostname -I | awk '{print $1}')
    dt=$(date +'%Y%m%d %H:%M:%S')
    echo "$0--${ip}--${dt}" >> /tmp/kp.log
    EOF
    
    cat > fault.sh << 'EOF'
    ip=$(ip addr|grep inet| grep 192.168 |awk '{print $2}')
    dt=$(date +'%Y%m%d %H:%M:%S')
    echo "$0--${ip}--${dt}" >> /tmp/kp.log
    EOF
    
    cat > stop.sh << 'EOF'
    ip=$(ip addr|grep inet| grep 192.168| awk '{print $2}')
    dt=$(date +'%Y%m%d %H:%M:%S')
    echo "$0--${ip}--${dt}" >> /tmp/kp.log
    EOF
    

    编写健康检查脚本

    该脚本对 Nginx 进程进行检测,如果发现 Nginx 进程没了则返回失败(1)

    cat > nginx_check.sh << 'EOF'
    #!/bin/bash
    result=`pidof nginx`
    if [ ! -z "${result}" ];
      then exit 0
      else exit 1
    fi
    EOF
    
  4. 编写完脚本后对这些脚本加 x 权限,并启动 Keepalived

    cd /tools/ && chmod +x *.sh
    systemctl restart keepalived.service
    

验证

  1. 访问 VIP 地址

    现在 web1(192.168.149.130)是 master

    访问 192.168.149.100:8080,可以看到访问成功了

    高可用解决方案 Keepalived 案例(keepalived + nginx)_第2张图片

  2. 切换主备

    关闭 web1 服务

    [root@nginx1 ~]# nginx -s stop
    

    然后再 web2 服务的主机可以看到 web2(192.168.149.131)获得了 VIP,升级成了主

    高可用解决方案 Keepalived 案例(keepalived + nginx)_第3张图片

    访问 VIP 地址(192.168.149.100:8080),可以发现访问到了 web2 服务器上

    高可用解决方案 Keepalived 案例(keepalived + nginx)_第4张图片

    之后重启 web1 看一下

    可以看到 web1 主机又变成了 master,因为没有配置抢占模式/非抢占模式,所以选举机制是优先级,web1 的优先级比 web2 要高,所以 web1 启动后就会把 master 角色拿过来


问题解决

查看 keepalived 系统日志:less /var/log/messages

  • Unable to access script /shell/nginx_check.sh

    selinux 禁止了这个脚本。keepalived 进程的安全上下文与脚本的安全上下文不一致,就算有 rwx 权限也无法执行

    • 最简单的解决方案就是关闭 selinux 功能:

      # 永久关闭 selinux
      sed -i "s\SELINUX=enforcing\SELINUX=disabled\g" /etc/selinux/config
      # 重启主机
      reboot
      
      # 临时关闭selinux,reboot服务器后失效
      etenforce 0
      
    • 解决方案2:将脚本转移到 /usr/libexec/keepalived 目录中

      这个目录的安全上下文是 keepalived_unconfined_script_exec_t,与 keepalived 进程的安全上下文一致

    • 解决方案3:修改 check.sh 的安全上下文为 keepalived 进程的安全上下文

      chcon -t keepalived_unconfined_sript_exec_it /etc/keepalived/nginx_check.sh
      

      keepalived_unconfined_script_exec_t 是一个在 SELinux 中用于标识 Keepalived 执行未限制脚本的上下文

      这个上下文允许 Keepalived 进程在执行脚本时绕过一些 SELinux 限制,从而可以在需要的情况下执行脚本

    # 查看 keepalived 进程的安全上下文
    ps -eZ | grep keepalived
    #输出:system_u:system_r:keepalived_t:s0 19689 ?	00:00:00 keepalived
    
    # 查看文件/目录的安全上下文
    ll -Z /etc/keepalived/check.sh
    #输出:-rwr-xr-x. root system_u:object_r:etc_t:s0
    
  • Disabling track script chk_nginx since not found

    在 VRRP 实例中添加 track_script { chk_nginx } 以启动脚本检测

  • warning default user ‘keepalived_script’for script execution does not exist - please create

    找不到 keepalived_script 这个用户组,开启下面的配置,如果找不到就使用 root

    在全局配置 global_defs 中添加 script_user root

    注:该配置非必需,日志打印也只是警告而已

  • SECURITY VIOLATION - scripts are being executed but script_security notenabled

    在全局配置 global_defs 中添加 enable_script_security

  • Unknown keyword:’}’、‘track_script{’、'chk_nginx 等等

    配置文件格式不正确:使用到大括号 { 的地方,确保正文与大括号间有空格。

  • Can't open PID file /var/run/nginx.pid (yet?) after start: No such fileor directory

    使用 systemctl start nginx 时,先调用的是 nginx.service,启动时 nginx.pid 文件并未生成

    在 /usr/lib/systemd/system/nginx.service 中 [service] 模块下添加 ExecStartPost=/bin/sleep 0.1

  • Can't open PID file /var/run/keepalived.pid (yet?) after start: No suchfile or directory

    使用 systemctl start keepalived 时,先调用的是 keepalived.service,启动时 keealived.pid 文件并未生成

    在 /usr/lib/systemd/system/keepalived.service 中 [service] 模块下添加 ExecStartPost=/bin/sleep 0.1


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