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：

Nginx 的安装与配置

1. 安装软件# 安装nginx以及拓展源yum install epel-release -yyum 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 "<h1>This is web1</h1>" > /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 "<h1>This is web2</h1>" > /usr/share/nginx/html/test.html
3. 启动 Nginxnginx -tnginx

Keepalived 的安装与配置

1. 安装 Keepalivedyum 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:mastervi /etc/keepalived/keepalived.conf``````! Configuration File for keepalivedglobal_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:slavevi /etc/keepalived/keepalived.conf``````! Configuration File for keepalivedglobal_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 /toolscat> master.sh <<'EOF'ip=$(hostname -I | awk '{print $1}')dt=$(date +'%Y%m%d %H:%M:%S')echo "$0--${ip}--${dt}" >> /tmp/kp.logEOFcat> backup.sh <<'EOF'ip=$(hostname -I | awk '{print $1}')dt=$(date +'%Y%m%d %H:%M:%S')echo "$0--${ip}--${dt}" >> /tmp/kp.logEOFcat> fault.sh <<'EOF'ip=$(ip addr|grep inet| grep 192.168 |awk '{print $2}')dt=$(date +'%Y%m%d %H:%M:%S')echo "$0--${ip}--${dt}" >> /tmp/kp.logEOFcat> stop.sh <<'EOF'ip=$(ip addr|grep inet| grep 192.168| awk '{print $2}')dt=$(date +'%Y%m%d %H:%M:%S')echo "$0--${ip}--${dt}" >> /tmp/kp.logEOF编写健康检查脚本该脚本对 Nginx 进程进行检测，如果发现 Nginx 进程没了则返回失败（1）cat> nginx_check.sh <<'EOF'#!/bin/bashresult=`pidof nginx`if [ ! -z "${result}" ]; then exit 0 else exit 1fiEOF
4. 编写完脚本后对这些脚本加 x 权限，并启动 Keepalivedcd /tools/ &&chmod +x *.shsystemctl 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
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，升级成了主访问 VIP 地址（192.168.149.100:8080），可以发现访问到了 web2 服务器上之后重启 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.shselinux 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 selinuxsed-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