keepalived： 防止单点故障，实现集群高可用
作用： 起初就是为了搭配lvs使用，因为lvs没有健康检查的作用，如果服务端有一个主机宕机，lvs还会交给该主机，为了避免这种情况的发生，所以使用keepalived搭配lvs使用，使其能够对后端有健康检查的功能，从而剔除掉不正常的主机。之后为了解决更多的问题对leepalived进行优化，使其实现了vrrp协议（虚拟路由冗余协议）从而能够解决单点故障，保证集群的高可用状态。
高可用： 防止集群中因为某个节点坏掉，而导致整个集群不能使用
高并发： 能够供多个客户端访问
单点故障： 集群中一个节点坏掉
原理： keepalived如何实现故障转移，解决单点故障，是因为keepalived可以设值虚拟IP，这个虚拟IP是实际工作的IP，当keepalived配置了虚拟IP，这个虚拟IP就会有一定的特定，会变成漂移IP。这个IP漂移到那个主机，就是那个主机正在工作，keepalived分为主和备（master和backup），这回定期给备份发动消息（消息时间为1s）从而证明自己在工作，如果当备份接收不到主的消息，则会认为宕机，之后漂移IP将会漂移到备档主恢复以后，漂移IP优惠漂移到主上面，继续为整个集群工作

服务名

IP

客户端

192.168.1.1

lvs主+keepalived主

192.168.1.2/虚拟IP192.168.1.200

lvs备+keepalived备

192.168.1.3

web1

192.168.1.4

web2

192.168.1.5

操作：
lvs主+keepalived主

[root@CentOS2 ~]# yum -y install popt-devel kernel-devel openssl-devel
[root@CentOS2 ~]# tar zxf keepalived-1.2.13.tar.gz 
[root@CentOS2 ~]# cd keepalived-1.2.13/
[root@CentOS2 keepalived-1.2.13]# ./configure --prefix=/ --with-kernel-dir=/usr/src/kernel && make -j4 && make install
[root@CentOS ~]# modprobe ip_vs
[root@CentOS2 ~]# yum -y install ipvsadm
[root@Centos2 ~]# cp /etc/keepalived/keepalived.conf /etc/keepalived/keepalived.bak
[root@CentOS2 ~]# vim /etc/keepalived/keepalived.conf
global_defs {	#邮件地址
   notification_email {
     acassen@firewall.loc
     failover@firewall.loc
     sysadmin@firewall.loc
   }
   notification_email_from Alexandre.Cassen@firewall.loc	#发件人的信息
   smtp_server 192.168.200.1	#邮件服务器
   smtp_connect_timeout 30		#和邮件服务器连接的超时时间
   router_id LVS_DEVEL			#节点标识
}
vrrp_instance VI_1 {		#vrrp协议组名
    state MASTER			#主节点
    interface ens33			#用来接收漂移IP的网卡
    virtual_router_id 51	#server_id 一个组的id一致
    priority 100
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }   
    virtual_ipaddress {
        192.168.1.200
    }   
}
virtual_server 192.168.1.200 80 {
    delay_loop 6	#对后端健康检查时间
    lb_algo rr		#调度算法 rr
    lb_kind DR		#工作模式 直接路由
    nat_mask 255.255.255.0	#子网掩码
    persistence_timeout 0	#会话保持时间
    protocol TCP			#tcp连接

    real_server 192.168.1.4 80 {	#后端真是主机
        weight 1	#权重
            connect_port 80	#连接端口
            connect_timeout 3	#超时时间
            nb_get_retry 3	#节点连接的成功次数
            delay_before_retry 3	#每个多就建立连接
    }
    real_server 192.168.1.5 80 {
        weight 1
            connect_port 80
            connect_timeout 3
            nb_get_retry 3
            delay_before_retry 3
    }
}
[root@CentOS2 ~]# scp /etc/keepalived/keepalived.conf root@192.168.1.3:/etc/keepalived/keepalived.conf 
[root@CentOS2 ~]# service keepalived start

lvs备+keepalived备

[root@Centos3 ~]# yum -y install popt-devel kernel-devel openssl-devel
[root@Centos3 ~]# tar zxf keepalived-1.2.13.tar.gz 
[root@Centos3 ~]# cd keepalived-1.2.13/
[root@Centos3 keepalived-1.2.13]# ./configure --prefix=/ --with-kernel-dir=/usr/src/kernel && make -j4 && make install
[root@Centos3 ~]# modprobe ip_vs
[root@CentOS3 ~]# yum -y install ipvsadm
[root@Centos3 ~]# cp /etc/keepalived/keepalived.conf /etc/keepalived/keepalived.bak
[root@Centos3 ~]# vim /etc/keepalived/keepalived.conf
#更改为以下内容
16     state BACKUP
19     priority 90

web端

#web1
[root@CentOS4 ~]# yum -y install httpd
[root@CentOS4 ~]# echo "192.168.1.4" > /var/www/html/index.html
[root@CentOS4 ~]# systemctl start httpd
[root@CentOS4 ~]# netstat -anput | grep 80
tcp6       0      0 :::80                   :::*                    LISTEN      56025/httpd  
[root@CentOS4 ~]# cd /etc/sysconfig/network-scripts/
[root@CentOS4 network-scripts]# cp ifcfg-lo ifcfg-lo:0
[root@CentOS4 network-scripts]# vim ifcfg-lo:0
#需要更改的东西
DEVICE=lo:0
IPADDR=192.168.1.200
NETMASK=255.255.255.255
NAME=lo
[root@CentOS4 network-scripts]# systemctl restart network
[root@CentOS4 network-scripts]# route add -host 192.168.1.200 dev lo:0
[root@CentOS4 network-scripts]# vim /etc/sysctl.conf
#在末尾处添加
net.ipv4.conf.lo.arp_ignore = 1
net.ipv4.conf.all.arp_ignore = 1
net.ipv4.conf.default.arp_ignore = 1
net.ipv4.conf.lo.arp_announce = 2
net.ipv4.conf.all.arp_announce = 2
net.ipv4.conf.default.arp_announce = 2
[root@CentOS4 network-scripts]# sysctl -p
#web2
[root@centos5 ~]# yum -y install httpd
[root@centos5 ~]# echo "192.168.1.5" > /var/www/html/index.html
[root@centos5 ~]# systemctl start httpd
[root@centos5 ~]# netstat -anput | grep 80
tcp6       0      0 :::80                   :::*                    LISTEN      54759/httpd    
[root@centos5 ~]# cd /etc/sysconfig/network-scripts/
[root@centos5 network-scripts]# cp ifcfg-lo ifcfg-lo:0
[root@centos5 network-scripts]# vim ifcfg-lo:0
#更改以下内容
DEVICE=lo:0
IPADDR=192.168.1.200
NETMASK=255.255.255.255
NAME=lo
[root@centos5 network-scripts]# systemctl restart network
[root@centos5 network-scripts]# route add -host 192.168.1.200 dev lo:0
[root@centos5 network-scripts]# vim /etc/sysctl.conf
#在末尾处添加
net.ipv4.conf.lo.arp_ignore = 1
net.ipv4.conf.all.arp_ignore = 1
net.ipv4.conf.default.arp_ignore = 1
net.ipv4.conf.lo.arp_announce = 2
net.ipv4.conf.all.arp_announce = 2
net.ipv4.conf.default.arp_announce = 2
[root@centos5 network-scripts]# sysctl -p

客户端验证

[root@CentOS1 ~]# curl 192.168.1.200
192.168.1.5
[root@CentOS1 ~]# curl 192.168.1.200
192.168.1.4

生产环境中不会设置主，会设置两个从，会根据优先级来争取漂移IP

[root@CentOS2 ~]# vim /etc/keepalived/keepalived.conf
 16     state BACKUP
 17     nopreempt	#开启非抢占模式