Keepalived study, dual-standby HA

First, the host installation　

　　1, extract

　　　　　　tar -zxvf keepalived-2.0.18.tar.gz
　　　2、解压后进入到解压出来的目录，看到会有configure，那么就可以做配置了　　　
　　　3、使用configure命令配置安装目录与核心配置文件所在位置：　　　　　　
　　　　　　./configure --prefix=/usr/local/keepalived --sysconf=/etc

　　　　　　prefix: keepalived installation location 
　　　　　　sysconf: Location keepalived core configuration file is located, fixed position, then changed to a different location keepalived not start, / var / log / messages will be error

　　　　　　A warning message may appear in the configuration process, as follows:

　　　　　　　　　　*** WARNING - this build will not support IPVS with IPv6. Please install libnl/libnl-3 dev libraries to support IPv6 with IPVS.

　　　　　　Installation libnl/libnl-3dependence

　　　　　　　　　　yum -y install libnl libnl-devel

　　　　　　Re- configurelook, this time OK.

　　　　4, installation keepalived

　　　　　　make && make install

　　　　5, into /etc/keepalived, the directory configuration file to the core keepalived

　　　　6, the command vim keepalived.conf to open the configuration file (the host)

global_defs {
   Route # id: keepalived currently installed host node identifier to ensure globally unique
   router_id keep_108
}

vrrp_instance VI_1 {
    MASTER state # indicates master or backup machine BACKUP
    state MASTER
    # NIC bind that instance by ip addr command to view, each machine is not the same
    interface ens33
    # Ensure consistent standby node can be
    virtual_router_id 51
    # Weights, master weight is generally higher than backup, if there is more that election, whose high weight, whoever elected
    priority 100
    # Primary synchronization check interval between standby, in seconds
    advert_int 2
    # Permissions password authentication to prevent illegal node enters
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    # Out of the virtual ip, there can be multiple (vip)
    virtual_ipaddress {
        192.168.1.161
    }
}

　　　　7, start keepalived

　　　　　　/usr/local/keepalived/sbin/keepalived

　　　　8, view the process

　　　　　　ps -ef | grep keepalived

　　　　9, see the vip, in the card ens33, one more 192.168.1.161, this is the virtual ip

　　　　　　ip addr

　　　　10, the keepalived registered as a system service, easy to lose command

　　　　　　Keepalived into the extracted directory

　　　　　　　　cd keepalived/etc/

　　　　　　　　cp init.d/keepalived /etc/init.d/

　　　　　　　　cp sysconfig/keepalived /etc/sysconfig/

　　　　　　　　systemctl daemon-reload

　　　　　　So you can use the following command to the

Second, the installation preparation

　　　　1 to 5 with the host

　　　　6, the command vim keepalived.conf to open the configuration file (backup unit)　　　

global_defs {
   router_id keep_101
}

vrrp_instance VI_1 {
    # Standby machine set BACKUP
    state BACKUP
    interface ens33
    virtual_router_id 51
    # Weight less than MASTER
    priority 80
    advert_int 2
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        # 注意：主备两台的vip都是一样的，绑定到同一个vip
        192.168.1.161
    }
}

　　　　7~10同主机

　　　　这样我请求192.168.1.161时，时请求的主机，当主机的keepalived挂掉后，我请求192.168.1.161时，请求自动到达备机，当主机恢复正常后请求又会到达主机，从而实现双击主备高可用。

三、keepalived实现nginx双机主备高可用

　　　　上边可知，主备机的切换是基于keepalived是否挂掉实现的，那么如何实现当主机nginx挂掉，自动切换到备机nginx呢？那就需要让keepalived去检测本机的nginx是否正常，如果发现nginx进程不在了，尝试重启nginx，如果重启失败，那么杀掉keepalived的进程，从而让请求到达备机。下边实现keepalived绑定nginx

　　　　1. 增加Nginx重启检测脚本

　　　　　　vim /etc/keepalived/check_nginx_alive_or_not.sh

#!/bin/bash

A=`ps -C nginx --no-header |wc -l`
# 判断nginx是否宕机，如果宕机了，尝试重启
if [ $A -eq 0 ];then
    /usr/local/nginx/sbin/nginx
    # 等待一小会再次检查nginx，如果没有启动成功，则停止keepalived，使其启动备用机
    sleep 3
    if [ `ps -C nginx --no-header |wc -l` -eq 0 ];then
        killall keepalived
    fi
fi

　　　　　　　增加运行权限

　　　　　　　　chmod +x /etc/keepalived/check_nginx_alive_or_not.sh

　　　　2. 在/etc/keepalived/keepalived.conf中添加下边两段

vrrp_script check_nginx_alive {
    script "/etc/keepalived/check_nginx_alive_or_not.sh"
    interval 2 # 每隔两秒运行上一行脚本
    weight 10 # 如果脚本运行成功，则升级权重+10
}

track_script {
    check_nginx_alive   # 追踪 nginx 脚本
}

　　　　最终是这样的：

　　　　3. 重启Keepalived使得配置文件生效

　　　　　　systemctl restart keepalived