什么是双机热备

双机热备，也叫高可用服务，主要解决单点故障问题。

高可用常用软件keepalive

keepalive在主备机器上都必须安装,yum, 主要的任务是通过vrrp虚拟路由协议来进行心跳检测。

安装软件

当前的环境

安装步骤

1. 安装软件

yum -y install keepalived 

2. 修改配置文件
   在master主机上，修改如下，主要是看优先级不能错，和state不能错
   virutal_router_id在同一个组高可用下需要相同，且局域网内部需要唯一。

[root@db01 keepalived]# cat keepalived.conf
global_defs {
   notification_email {
     acassen@firewall.loc
     failover@firewall.loc
     sysadmin@firewall.loc
   }
   notification_email_from Alexandre.Cassen@firewall.loc
   router_id LVS_DEVEL
   vrrp_skip_check_adv_addr
   vrrp_garp_interval 0
   vrrp_gna_interval 0
}

vrrp_instance VI_1 {
    state MASTER
    interface eth0
    virtual_router_id 51
    priority 100
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        192.168.10.30
   }
}

在slave 机器上，如下

[root@db01 keepalived]# cat keepalived.conf
global_defs {
   notification_email {
     acassen@firewall.loc
     failover@firewall.loc
     sysadmin@firewall.loc
   }
   notification_email_from Alexandre.Cassen@firewall.loc
   router_id LVS_DEVEL
   vrrp_skip_check_adv_addr
   vrrp_garp_interval 0
   vrrp_gna_interval 0
}

vrrp_instance VI_1 {
    state BACKUP
    interface eth0
    virtual_router_id 51
    priority 80
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        192.168.10.30
   }
}

测试

1. 主机上和备份机上 启动keepakive

   systemctl start keepalived

2. 可以看到主机上获取了VIP.

[root@master keepalived]# systemctl start keepalived
[root@master keepalived]# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host  valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000  link/ether 52:54:00:e0:98:b0 brd ff:ff:ff:ff:ff:ff
    inet 192.168.10.174/24 brd 192.168.10.255 scope global noprefixroute dynamic eth0       valid_lft 631065sec preferred_lft 631065sec    inet 192.168.10.30/32 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::7ef4:cacc:9f94:b9ca/64 scope link tentative noprefixroute dadfailed
       valid_lft forever preferred_lft forever
    inet6 fe80::7164:8429:bba:c759/64 scope link tentative noprefixroute dadfailed
       valid_lft forever preferred_lft forever
    inet6 fe80::40fd:5b2:4af7:b811/64 scope link tentative noprefixroute dadfailed
       valid_lft forever preferred_lft forever

3. 把主机上 的keepalive停掉，模拟宕机。

   systemctl stop keepalived

可以看到备份机器获取了IP。

[root@db01 keepalived]# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 52:54:00:c5:e3:b2 brd ff:ff:ff:ff:ff:ff
    inet 192.168.10.153/24 brd 192.168.10.255 scope global noprefixroute dynamic eth0
       valid_lft 619941sec preferred_lft 619941sec
    inet 192.168.10.30/32 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::cfeb:25dd:a383:2d45/64 scope link tentative noprefixroute dadfailed
       valid_lft forever preferred_lft forever
    inet6 fe80::c142:2d8d:c705:21e0/64 scope link tentative noprefixroute dadfailed
       valid_lft forever preferred_lft forever
    inet6 fe80::9224:32eb:8e7b:df11/64 scope link tentative noprefixroute dadfailed
       valid_lft forever preferred_lft forever

自动做nginx生存测试或者完备测试进行漂移

1. 首先主机上创建检查nginx是否能够工作的脚本，如果不能工作，就直接关闭keepalived服务，让备份机器获取到VIP。

cat <<EOF >/opt/checknginx.sh
#!/bin/bash
running=` curl -I localhost 2>/dev/null | wc -l `
if [ $running -eq 0 ] ; then
      exit 1
else
      exit 0
fi
EOF

2. 修改主机上的keepalived配置文件，使得能够让keepalive自动执行脚本。

! Configuration File for keepalived

global_defs {
   notification_email {
     acassen@firewall.loc
     failover@firewall.loc
     sysadmin@firewall.loc
   }
   notification_email_from Alexandre.Cassen@firewall.loc
   router_id LVS_DEVEL
   vrrp_skip_check_adv_addr
   vrrp_garp_interval 0
   vrrp_gna_interval 0
}
！定义脚本名称，执行指定的脚本。
！interval 3表示 3秒钟执行一次。
vrrp_script nginx {
    script "/opt/checknginx.sh"
    interval 3
    weight -30
    fall 2
    rise 1
}

vrrp_instance VI_1 {
    state MASTER
    interface eth0
    virtual_router_id 251
    priority 100
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        192.168.10.30
    }
! 这里要增加检查的脚本名称 
   track_script {
        nginx
   }

}

测试

步骤一

启动ngnix,启动2个keeplive

步骤二

关闭主机上的nginx服务，会发现VIP会漂移到备份机器。