主主 高可用keepalived应用

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* 在两台主备节点编辑keepalived配置文件

* 主节点主机上：
```
]# vim /etc/keepalived/keepalived.conf
------------------------------------------------------------------------------
global_defs {
    notification_email {
        [size=1em]root@localhost
    }
    notification_email_from kaadmin@magedu.com
    smtp_server 172.0.0.1
    smtp_connect_timeout 30
    router_id node1
    vrrp_mcast_group4 224.0.11.18
}


vrrp_script chk_down {
    script "[[ -f /etc/keepalived/down ]] && exit 1 || exit 0"
    interval 2
    weight -5
}


vrrp_script chk_httpd {
    script "killall -0 httpd"
    interval 2
    weight 5
}


vrrp_instance VI_1 {
    state MASTER
    interface eno16777736
    virtual_router_id 11
    priority 100
    advert_int 1
    authentication {
        [size=1em]auth_type PASS
        [size=1em]auth_pass vHFHLlTA
    }

    virtual_ipaddress {
        [size=1em]172.18.11.7 dev eno16777736 label eno16777736:0
    }

    track_script {
        [size=1em]chk_down
    }

    notify_master "/etc/keepalived/notify.sh master"
    notify_backup "/etc/keepalived/notify.sh backup"
    notify_fault "/etc/keepalived/notify.sh fault"
}


vrrp_instance VI_2 {
    state BACKUP
    interface eno16777736
    virtual_router_id 12
    priority 98
    advert_int 1
    authentication {
        [size=1em]auth_type PASS
        [size=1em]auth_pass RHFHLlTA
    }

    virtual_ipaddress {
        [size=1em]172.18.11.77 dev eno16777736 label eno16777736:1
    }
    track_script {
        [size=1em]chk_down
    }

    [size=1em]notify_master "/etc/keepalived/notify.sh master"
    notify_backup "/etc/keepalived/notify.sh backup"
    notify_fault "/etc/keepalived/notify.sh fault"
}
```


* 备节点主机上：
  ```
    ]# vim /etc/keepalived/keepalived.conf
    ---------------------------------------------------------------
    vrrp_instance VI_1 {
        [size=1em]state BACKUP
        [size=1em]interface eno16777736
        [size=1em]virtual_router_id 11
        [size=1em]priority 98
        [size=1em]advert_int 1
        [size=1em]authentication {
            [size=1em]auth_type PASS
            [size=1em]auth_pass vHFHLlTA
        [size=1em]}
[size=1em]

        [size=1em]virtual_ipaddress {
            [size=1em]172.18.11.7 dev eno16777736 label eno16777736:0
        [size=1em]}
[size=1em]

        [size=1em]track_script {
            [size=1em]chk_down
        [size=1em]}
[size=1em]

        [size=1em]notify_master "/etc/keepalived/notify.sh master"
        [size=1em]notify_backup "/etc/keepalived/notify.sh backup"
        [size=1em]notify_fault "/etc/keepalived/notify.sh fault"
    }


    vrrp_instance VI_2 {
        state MASTER
        [size=1em]interface eno16777736
        [size=1em]virtual_router_id 12
        [size=1em]priority 100
        [size=1em]advert_int 1
        [size=1em]authentication {
            [size=1em]auth_type PASS
            [size=1em]auth_pass RHFHLlTA
        [size=1em]}
[size=1em]

        [size=1em]virtual_ipaddress {
            [size=1em]172.18.11.77 dev eno16777736 label eno16777736:1
        [size=1em]}
[size=1em]

        [size=1em]track_script {
            [size=1em]chk_down
        [size=1em]}
[size=1em]

        [size=1em]notify_master "/etc/keepalived/notify.sh master"
        [size=1em]notify_backup "/etc/keepalived/notify.sh backup"
        [size=1em]notify_fault "/etc/keepalived/notify.sh fault"
    }


        [size=1em]主备节点都关闭keepalived服务；
    ]# systemctl stop keepalived.service

        [size=1em]先启动B备节点的keepalived服务；
    ]# systemctl start keepalived.service

    ]# ifconfig
        [size=1em]可见有两个VIP的地址都获得了即：
        [size=1em]172.18.11.7
        [size=1em]172.18.11.77
        [size=1em]此时，只有B节点，所以都当做主服务；
[size=1em]

        [size=1em]再启动A节点的keepalived服务；
    ]# systemctl start keepalived.service

    ]# ifconfig
        [size=1em]则发现，获得了VIP为172.18.11.7；
[size=1em]

       [size=1em] [size=1em]在A节点创建一个down文件
    ]# touch down

    ]# ifconfig
        [size=1em]此时VIP丢失；
[size=1em]

        [size=1em]在B节点查看：
    ]# ifconfig
        [size=1em]获得成为了两个VIP的主用；

        [size=1em]同理，在B节点创建一个down文件，A节点会成为两个VIP的主用；
  ```
以上演示就是互为主备的高可用keepalived应用

**如果再加上vrrp_script的脚本监控nginx服务，于是这就双主模型的nginx节点；如果nginx工作在反代模式就是高可用调度器；把配置文件中httpd改为nginx，再调用[size=1em]即可；**