HA 即 （high available）高可用，又被叫做双机热备，用于关键性业务。 简单理解就是，有两台机器A和B，正常是A提供服务，B待命闲置，当A宕机或服务宕掉，会切换至B机器继续提供服务。常用实现高可用的开源软件有heartbeat和keepalived，其中keepalived有负载均衡的功能。
开机启动后，拷贝ifcfg-eth0 到 ifcfg-eth1，修改DEVICE为eth1，ip地址设为：192.168.11.20
# cd /etc/sysconfig/network-scripts/
# cp ifcfg-eth0 ifcfg-eth1
# cat ifcfg-eth1
DEVICE=eth1
TYPE=Ethernet
ONBOOT=yes
NM_CONTROLLED=yes
BOOTPROTO=static
IPADDR=192.168.11.20
设置完成后，重启网卡，ifconfig查看eth0、eth1的ip地址；
# /etc/init.d/network restart
#ifconfig
主机的配置：
hostname hello
eth0：192.168.20.20
eth1：192.168.11.20
从机的配置：
hostname web
eth0：192.168.20.30
eth1：192.168.11.30
1、设置hostname，分别为hello和 web；
2、主从都需要关闭防火墙；关闭selinux；
# iptables -F
# setenforce 0
setenforce: SELinux is disabled
3、 vi /etc/hosts //主从都需要增加内容如下：
192.168.20.20 hello
192.168.20.30 web
4、安装epel扩展源
# yum install -y epel-release
5、两个机器都安装heartbeat、libnet
#yum install -y heartbeat* libnet nginx
nginx做代理服务；
6、主上（hello）配置
Heartbeat软件的安装目录为/etc/ha.d目录；
拷贝配置文件的模板到/etc/ha.d目录；
cd /usr/share/doc/heartbeat-3.0.4/
cp authkeys ha.cf haresources /etc/ha.d/
cd /etc/ha.d
vi authkeys //去掉前面的#号，或加入下面的内容：
auth 3
3 md5 Hello!
更改权限为600
chmod 600 authkeys
vi haresources //加入
hello 192.168.11.100/24/eth1:0 nginx
192.168.11.100 ip地址是流动ip，虚拟ip；用来绑定服务的；子网掩码为24位；使用eth1:0绑定虚拟ip，并运行nginx进行测试；
注意：两台主机的haresources文件设置必须完全一致。
vi ha.cf //更改为如下内容：
debugfile /var/log/ha-debug
logfile /var/log/ha-log
logfacility local0
keepalive 2
deadtime 30
warntime 10
initdead 60
udpport 694
ucast eth1 192.168.11.30
auto_failback on
node hello
node web
ping 192.168.11.1
respawn hacluster /usr/lib/heartbeat/ipfail
7、把主上的三个配置拷贝到从上：
#cd /etc/ha.d/
#scp authkeys ha.cf haresources web:/etc/ha.d/
8、从上(web) 只需要编辑ha.cf
vi /etc/ha.d/ha.cf //只需要更改一个地方
ucast eth1 192.168.11.30 改为 ucast eth1 192.168.11.20
9、启动heartbeat
先主，后从
#service heartbeat start
10、检查测试
ifconfig 查看是否有 eth1:0 出现则说明主已经开始工作；
[root@yong ~]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0C:29:43:3D:32
inet addr:192.168.20.20 Bcast:192.168.20.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fe43:3d32/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:433 errors:0 dropped:0 overruns:0 frame:0
TX packets:429 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:37095 (36.2 KiB) TX bytes:75381 (73.6 KiB)
Interrupt:18 Base address:0x2000
eth1 Link encap:Ethernet HWaddr 00:0C:29:43:3D:3C
inet addr:192.168.11.20 Bcast:192.168.11.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fe43:3d3c/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:396 errors:0 dropped:0 overruns:0 frame:0
TX packets:399 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:83641 (81.6 KiB) TX bytes:89725 (87.6 KiB)
Interrupt:18 Base address:0x2080
eth1:0 Link encap:Ethernet HWaddr 00:0C:29:43:3D:3C
inet addr:192.168.11.100 Bcast:192.168.11.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
Interrupt:18 Base address:0x2080
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
查看是否有nginx进程、heartbeat进程；
[root@yong ha.d]# ps aux |grep nginx
root 3731 0.0 0.1 5000 632 ? Ss 10:52 0:00 nginx: master process /usr/local/nginx/sbin/nginx -c /usr/local/nginx/conf/nginx.conf
nobody 3732 0.0 0.1 5200 984 ? S 10:52 0:00 nginx: worker process
[root@yong ha.d]# ps aux |grep heartbeat
root 2765 0.3 1.3 6684 6676 ? SLs 10:44 0:01 heartbeat: master control process
root 2770 0.0 1.2 6488 6480 ? SL 10:44 0:00 heartbeat: FIFO reader
root 2771 0.0 1.2 6484 6476 ? SL 10:44 0:00 heartbeat: write: ucast eth1
root 2772 0.0 1.2 6484 6476 ? SL 10:44 0:00 heartbeat: read: ucast eth1
root 2773 0.0 1.2 6484 6476 ? SL 10:44 0:00 heartbeat: write: ping 192.168.11.1
root 2774 0.0 1.2 6484 6476 ? SL 10:44 0:00 heartbeat: read: ping 192.168.11.1
498 2787 0.0 0.2 5380 1488 ? S 10:45 0:00 /usr/lib/heartbeat/ipfail
11、测试1：主上故意禁ping
#iptables -I INPUT -p icmp -j DROP
Windows客户端一直ping 192.168.11.100 ，一直通，禁止ping之后中间会中断一会，之后一直通；
在从上ifconfig查看出现eth1:0，查看nginx进程也有，说明转换到从机器上运行；
[root@web ~]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0C:29:97:C3:EC
inet addr:192.168.20.30 Bcast:192.168.20.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fe97:c3ec/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:460 errors:0 dropped:0 overruns:0 frame:0
TX packets:469 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:37104 (36.2 KiB) TX bytes:101866 (99.4 KiB)
Interrupt:19 Base address:0x2000
eth1 Link encap:Ethernet HWaddr 00:0C:29:97:C3:F6
inet addr:192.168.11.30 Bcast:192.168.11.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fe97:c3f6/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1022 errors:0 dropped:0 overruns:0 frame:0
TX packets:1035 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:191275 (186.7 KiB) TX bytes:182393 (178.1 KiB)
Interrupt:18 Base address:0x2080
eth1:0 Link encap:Ethernet HWaddr 00:0C:29:97:C3:F6
inet addr:192.168.11.100 Bcast:192.168.11.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
Interrupt:18 Base address:0x2080
12、测试2：主上停止heartbeat服务
1 #service heartbeat stop
Windows客户端一直ping 192.168.11.100 ，一直通，停止心跳服务后中间会中断一会，之后一直通；
在从上ifconfig查看出现eth1:0，查看nginx进程也有，说明转换到从机器上运行；
13、测试3：测试脑裂，主和从都停掉eth1网卡；
eth1网卡禁用，ifdown eth1 心跳线断了之后，会发生脑裂；主从之间连接断了，从在死亡时间没收到主的心跳，则认为主死亡。
主死了，从机器接管服务，从机器使用虚拟ip地址，主和从都在运行服务；
主机器没有eth1网卡，一直运行nginx；
[root@yong ha.d]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0C:29:43:3D:32
inet addr:192.168.20.20 Bcast:192.168.20.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fe43:3d32/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:11442 errors:0 dropped:0 overruns:0 frame:0
TX packets:15376 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:842833 (823.0 KiB) TX bytes:10226838 (9.7 MiB)
Interrupt:18 Base address:0x2000
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:1163 errors:0 dropped:0 overruns:0 frame:0
TX packets:1163 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:150095 (146.5 KiB) TX bytes:150095 (146.5 KiB)
[root@yong ha.d]# ps aux |grep nginx
root 11686 0.0 0.1 5000 636 ? Ss 14:27 0:00 nginx: master process /usr/local/nginx/sbin/nginx -c /usr/local/nginx/conf/nginx.conf
nobody 11687 0.0 0.1 5200 988 ? S 14:27 0:00 nginx: worker process
从机器查看地址，eth1:0出现
[root@localhost ha.d]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0C:29:97:C3:EC
inet addr:192.168.20.30 Bcast:192.168.20.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fe97:c3ec/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:7901 errors:0 dropped:0 overruns:0 frame:0
TX packets:5891 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:603592 (589.4 KiB) TX bytes:2094606 (1.9 MiB)
Interrupt:19 Base address:0x2000
eth1 Link encap:Ethernet HWaddr 00:0C:29:97:C3:F6
inet6 addr: fe80::20c:29ff:fe97:c3f6/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:20774 errors:0 dropped:0 overruns:0 frame:0
TX packets:59144 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:3513861 (3.3 MiB) TX bytes:12998603 (12.3 MiB)
Interrupt:18 Base address:0x2080
eth1:0 Link encap:Ethernet HWaddr 00:0C:29:97:C3:F6
inet addr:192.168.11.100 Bcast:0.0.0.0 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
Interrupt:18 Base address:0x2080
[root@localhost ha.d]# ps aux |grep nginx
root 8938 0.0 0.0 3684 584 ? Ss 14:37 0:00 nginx: master process /usr/local/nginx/sbin/nginx -c /usr/local/nginx/conf/nginx.conf
nobody 8940 0.0 0.1 4936 2008 ? S 14:37 0:00 nginx: worker process
nobody 8941 0.0 0.2 4936 2064 ? S 14:37 0:00 nginx: worker process
14、测试4：设置auto_failback off
主从都需要配置，启动heartbeat，主上禁止ping之后，跳转到从机器，主恢复ping之后，也不会跳转到主，一直是从机器提供服务；
HA高可用搭建完毕；