原理

实现原理是靠 TCP/IP 的 ARP 协议。因为 IP 地址只是一个逻辑 地址，在以太网中 MAC 地址才是真正用来进行数据传输的物理地址，每台主机中都有一个 ARP 缓存，存储同一个网络内的 IP 地址与 MAC 地址的对应关系，以太网中的主机发送数据时会先从这个缓存中查询目标 IP 对应的 MAC 地址，会向这个 MAC 地址发送数据。操作系统会自动维护这个缓存。

命令

yum install -y keepalived # 安装

systemctl status keepalived # 查看服务状态
systemctl restart keepalived # 启动服务
systemctl stop keepalived # 停止服务

systemctl enable keepalived # 开机启动
systemctl disable keepalived # 开机禁用

cat /etc/keepalived/keepalived.conf # 查看配置
vi /etc/keepalived/keepalived.conf # 编辑配置

ip addr show eth0 # 查看网卡信息，eth0 为网卡名

配置

Master

! Configuration File for keepalived

global_defs {
    script_user root
    router_id LVS_DEVEL
    vrrp_skip_check_adv_addr
    vrrp_strict
    vrrp_garp_interval 0
    vrrp_gna_interval 0
}

vrrp_instance VI_1 {
    state MASTER    # 主备配置不一致
    interface eth0
    virtual_router_id 51
    priority 100
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass aaaaaaa   # 主备该配置必须一样
    }
    virtual_ipaddress {
        192.168.100.199/24  # VIP，可配置多个
    }

    # 当这台机器成为 Master 时发送通知
    # notify_master "/etc/keepalived/notify.sh 192.168.100.199 master" 
    # notify_backup "/etc/keepalived/notify.sh 192.168.100.199 backup"
    # notify_fault  "/etc/keepalived/notify.sh 192.168.100.199 fault"
}

Backup

! Configuration File for keepalived

global_defs {
    script_user root
    router_id LVS_DEVEL
    vrrp_skip_check_adv_addr
    vrrp_strict
    vrrp_garp_interval 0
    vrrp_gna_interval 0
}

vrrp_instance VI_1 {
    state BACKUP    # 主备配置不一致
    interface eth0
    virtual_router_id 51
    priority 90     # 备机权重比主机低
    advert_int 1
    nopreempt       # 防止争抢 VIPA，只有 state 设置为 BACKUP 才能使用该选项
    authentication {
        auth_type PASS
        auth_pass aaaaaaa   # 主备该配置必须一样
    }
    virtual_ipaddress {
        192.168.100.199/24  # VIP，可配置多个
    }
}

引用

https://www.cnblogs.com/schaepher/p/12842624.html
https://www.jianshu.com/p/11f6e16cf8d9

附

甲骨文免费的 Oracle 两台小鸡部署失败，默认网卡名为 ens3，或许姿势不对需要哪里配置一下，换到本地虚拟机部署成功，网卡名默认 eth0