Keepalived:
keepalived是基于vrrp协议实现的一个高可用集群解决方案，可以利用keepalived来解决单点故障问题，使用keepalived实现的高可用集群方案中，一般有两台服务器，一个是MASTER（主服务器），另一个是BACKUP（备用服务器），这个集群中对外提供一个虚拟IP，MASTER服务器会定时发送特定信息给BACKUP服务器，当BACKUP服务器接收不到MASTER发送的消息时，BACKUP服务器会接管虚拟IP，继续提供服务。
当keepalived基于主备模式实现高可用时，提供服务的只有一台主服务器，备服务器只有在主服务器出现故障时才能提供作用，这就造成了资源的浪费，所以keepalived可以通过实现双主模式来实现资源的利用。两台服务器都对外提供服务，并且当一台服务器出现故障时，这台IP地址就会转移到另外一台服务器上，继续提供服务。
keepalived双主模式图：
实验准备：
1、虚拟机 172.18.250.75 反向代理服务器
2、虚拟机 172.18.250.76 反向代理服务器
3、虚拟机 172.18.250.77 Web服务器
4、虚拟机 172.18.250.79 Web服务器
注意：iptables和selinux不会影响keepalived，两台服务时间要同步
一、安装keepalived服务
~]# yum -y install keepalived
编辑配置文件/etc/keepalived/keepalived.conf
~]# vim /etc/keepalived/keepalived.conf
global_defs {
notification_email {
root@localhost
}
notification_email_from Alexandre.Cassen@firewall.loc
smtp_server 127.0.0.1
smtp_connect_timeout 30
router_id node1
vrrp_mcast_group4 224.0.74.18
}
vrrp_instance VI_1 {
state MASTER
interface eth0
virtual_router_id 151
priority 100
advert_int 1
authentication {
auth_type PASS
auth_pass 1111
}
virtual_ipaddress {
172.18.250.99 dev eth0 label eth0:0
}
}
vrrp_instance VI_2 {
state BACKUP
interface eth0
virtual_router_id 152
priority 98
advert_int 1
authentication {
auth_type PASS
auth_pass 2222
}
virtual_ipaddress {
172.18.250.100 dev eth0 label eth0:1
}
}另一台上面也配置相同的文件（250.76）
~]# vim /etc/keepalived/keepalived.conf
global_defs {
notification_email {
root@localhost
}
notification_email_from Alexandre.Cassen@firewall.loc
smtp_server 127.0.0.1
smtp_connect_timeout 30
router_id node1
vrrp_mcast_group4 224.0.74.18
}
vrrp_instance VI_1 {
state BACKUP
interface eth0
virtual_router_id 151
priority 98
advert_int 1
authentication {
auth_type PASS
auth_pass 1111
}
virtual_ipaddress {
172.18.250.99 dev eth0 label eth0:0
}
}
vrrp_instance VI_2 {
state MASTER
interface eth0
virtual_router_id 152
priority 100
advert_int 1
authentication {
auth_type PASS
auth_pass 2222
}
virtual_ipaddress {
172.18.250.100 dev eth0 label eth0:1
}
}配置完后启动keepalived服务：
]# service keepalived start Starting keepalived: [ OK ] ]# ifconfig eth0:0 Link encap:Ethernet HWaddr 00:0C:29:C5:A4:6B inet addr:172.18.250.99 Bcast:0.0.0.0 Mask:255.255.255.255 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 ]# ifconfig eth0:1 Link encap:Ethernet HWaddr 00:0C:29:F6:9E:DF inet addr:172.18.250.100 Bcast:0.0.0.0 Mask:255.255.255.255 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
这样就实现了keepalived的双主模式，测试下如果一台keepalived服务器down,地址会不会转移到另一台服务。
]# service keepalived stop Stopping keepalived: [ OK ] ]# ifconfig eth0:0 Link encap:Ethernet HWaddr 00:0C:29:F6:9E:DF inet addr:172.18.250.99 Bcast:0.0.0.0 Mask:255.255.255.255 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 eth0:1 Link encap:Ethernet HWaddr 00:0C:29:F6:9E:DF inet addr:172.18.250.100 Bcast:0.0.0.0 Mask:255.255.255.255 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
地址能转移。也可以通过vrrp_script脚本来实现keepalived的IP地址转移。
编辑配置文件：
~]# vim /etc/keepalived/keepalived.conf
vrrp_script ck_down {
script "[[ -e /etc/keepalived/down ]] && exit 1 || exit 0" //如果down文件存在，则返回错误码
weight -5 //返回错误码后权重就减5
interval 2 //2秒钟扫描一次文件
}
在两个虚拟节点中调用此脚本：
track_script {
ch_down
}
重启keepalived服务：
]# service keepalived restart
Stopping keepalived: [ OK ]
Starting keepalived: [ OK ]
测试：
]# touch down
]# ls
down keepalived.conf keepalived.conf.bak
]# ifconfig
eth0:0 Link encap:Ethernet HWaddr 00:0C:29:F6:9E:DF
inet addr:172.18.250.99 Bcast:0.0.0.0 Mask:255.255.255.255
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
eth0:1 Link encap:Ethernet HWaddr 00:0C:29:F6:9E:DF
inet addr:172.18.250.100 Bcast:0.0.0.0 Mask:255.255.255.255
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1已经转移到另一台服务器上来了。
]# rm down ]# ifconfig eth0:0 Link encap:Ethernet HWaddr 00:0C:29:C5:A4:6B inet addr:172.18.250.99 Bcast:0.0.0.0 Mask:255.255.255.255 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
双主模型就是这样实现。
二、通过脚本实现反向代理服务nginx的高可用
~]# yum -y install nginx
编辑配置文件：
~]# vim /etc/keepalived/keepalived.conf
vrrp_script chk_nginx_down {
script "killall -0 nginx" //查看nginx进程是否存在
weight -5
interval 2
}
在两个虚拟节点中添加调用此脚本：
track_script {
ch_down
chk_nginx_down
}重启服务：
]# service keepalived restart Stopping keepalived: [ OK ] Starting keepalived: [ OK ]
测试如果一台nginx服务挂了，地址会不会转移
]# nginx -s stop ]# ifconfig eth0 Link encap:Ethernet HWaddr 00:0C:29:C5:A4:6B inet addr:172.18.250.75 Bcast:172.18.255.255 Mask:255.255.0.0 inet6 addr: fe80::20c:29ff:fec5:a46b/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:122298 errors:0 dropped:0 overruns:0 frame:0 TX packets:8029 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:39436766 (37.6 MiB) TX bytes:918430 (896.9 KiB)
IP地址立马转移到另一台服务器上，所以实现了nginx的高可用。
keepalived也可以实现Web服务器的高可用，可以参考我的前一篇博客keepalived实现LVS集群的高可用。
