環境
centos 64位
http://www.osyunwei.com/archives/7566.html
Keepalived 是一種高性能的服務器高可用或熱備解決方案，Keepalived可以用來防止服務器單點故障(單點故障是指一旦某一點出現故障就會導致整個系統架構的不可用)的發生，通過配合Nginx可以實現web前端服務的高可用。
Keepalived實現的基礎是VRRP協議，Keepalived就是巧用VRRP協議來實現高可用性(HA)的.
VRRP(Virtual Router Redundancy Protocol)協議是用於實現路由器冗餘的協議，VRRP協議將兩臺或多臺路由器設備虛擬成一個設備，對外提供虛擬路由器IP(一個或多個)，而在路由器組內部，如果實際擁有這個對外IP的路由器如果工作正常的話就是MASTER，或者是通過算法選舉產生，MASTER實現針對虛擬路由器IP的各種網絡功能，如ARP請求，ICMP，以及數據的轉發等；其他設備不擁有該IP，狀態是BACKUP，除了接收MASTER的VRRP狀態通告信息外，不執行對外的網絡功能。當主機失效時，BACKUP將接管原先MASTER的網絡功能。
VRRP協議使用多播數據來傳輸VRRP數據，VRRP數據使用特殊的虛擬源MAC地址發送數據而不是自身網卡的MAC地址，VRRP運行時只有MASTER路由器定時發送VRRP通告信息，表示MASTER工作正常以及虛擬路由器IP(組)，BACKUP只接收VRRP數據，不發送數據，如果一定時間內沒有接收到MASTER的通告信息，各BACKUP將宣告自己成爲MASTER，發送通告信息，重新進行MASTER選舉狀態。
192.168.8.100 ： VIP（虛擬ip地址）
keepalived安裝在兩臺物理服務器上，並相互監控對方是否在正常運行。
當節點A正常的時候:節點A上的keepalived會將下面的信息廣播出去:
192.168.8.100 這個IP對應的MAC地址爲節點A網卡的MAC地址
圖中的其它電腦如客戶端和NodeB會更新自己的ARP表，對應192.168.8.100的MAC地址=節點A網卡的MAC地址。
當節點A發生故障的時候，節點B上的keepalived會檢測到，並且將下面的信息廣播出去:
192.168.8.100 這個IP對應的MAC地址爲節點B網卡的MAC地址
圖中的其它電腦如客戶端會更新自己的ARP表，對應192.168.8.100的MAC地址=節點B網卡的MAC地址。
四、安裝keepalived
下載keeplived：http://www.keepalived.org/software/keepalived-1.2.12.tar.gz
上傳keepalived-1.2.12.tar.gz到/usr/local/src目錄
cd /usr/local/src
tar zxvf keepalived-1.2.12.tar.gz
cd keepalived-1.2.12
./configure --prefix=/usr/local/keepalived #配置，必須看到以下提示，說明配置正確，才能繼續安裝
Use IPVS Framework : Yes
IPVS sync daemon support : Yes
Use VRRP Framework : Yes
make #編輯
make install #安裝
cp /usr/local/keepalived/etc/sysconfig/keepalived /etc/sysconfig/keepalived
mkdir /etc/keepalived
ln -s /usr/local/keepalived/etc/keepalived/keepalived.conf /etc/keepalived/
cp /usr/local/keepalived/sbin/keepalived /usr/sbin/
cp /usr/local/keepalived/etc/rc.d/init.d/keepalived /etc/rc.d/init.d/
chmod +x /etc/rc.d/init.d/keepalived #添加執行權限
chkconfig keepalived on #設置開機啓動
service keepalived start #啓動
service keepalived stop #關閉
service keepalived restart #重啓
五、配置keepalived
cp /usr/local/keepalived/etc/keepalived/keepalived.conf /usr/local/keepalived/etc/keepalived/keepalived.conf-bak
vi /usr/local/keepalived/etc/keepalived/keepalived.conf #編輯，修改爲以下代碼
#########################################################
#以下爲192.168.21.129服務器
! Configuration File for keepalived
global_defs {
notification_email {
}
notification_email_from [email protected]
smtp_server 192.168.200.1
smtp_connect_timeout 30
router_id LVS_DEVEL
}
vrrp_script chk_nginx {
script "/etc/keepalived/check_nginx.sh" #Nginx服務監控腳本
interval 2
weight 2
}
vrrp_instance VI_1 {
state MASTER
interface eth0
virtual_router_id 51
priority 100
advert_int 1
authentication {
auth_type PASS
auth_pass 1111
}
track_script {
chk_nginx #監測nginx進程狀態
}
virtual_ipaddress {
192.168.21.253
}
notify_master "/etc/keepalived/clean_arp.sh 192.168.21.253" #更新虛擬服務器（VIP）地址的arp記錄到網關
}
vrrp_instance VI_2 {
state BACKUP
interface eth0
virtual_router_id 52
priority 99
advert_int 1
authentication {
auth_type PASS
auth_pass 1111
}
virtual_ipaddress {
192.168.21.252
}
notify_master "/etc/keepalived/clean_arp.sh 192.168.21.252" #更新虛擬服務器（VIP）地址的arp記錄到網關
}
#########################################################
:wq! #保存退出
#########################################################
#以下爲192.168.21.130服務器
! Configuration File for keepalived
global_defs {
notification_email {
}
notification_email_from [email protected]
smtp_server 192.168.200.1
smtp_connect_timeout 30
router_id LVS_DEVEL
}
vrrp_script chk_nginx {
script "/etc/keepalived/check_nginx.sh" #Nginx服務監控腳本
interval 2
weight 2
}
vrrp_instance VI_1 {
state BACKUP
interface eth0
virtual_router_id 51
priority 99
advert_int 1
authentication {
auth_type PASS
auth_pass 1111
}
track_script {
chk_nginx #監測nginx進程狀態
}
virtual_ipaddress {
192.168.21.253
}
notify_master "/etc/keepalived/clean_arp.sh 192.168.21.253" #更新虛擬服務器（VIP）地址的arp記錄到網關
}
vrrp_instance VI_2 {
state MASTER
interface eth0
virtual_router_id 52
priority 100
advert_int 1
authentication {
auth_type PASS
auth_pass 1111
}
virtual_ipaddress {
192.168.21.252
}
notify_master "/etc/keepalived/clean_arp.sh 192.168.21.252" #更新虛擬服務器（VIP）地址的arp記錄到網關
}
#########################################################
:wq! #保存退出
六、設置nginx服務監控腳本
touch /usr/local/keepalived/check_nginx.sh
ln -s /usr/local/keepalived/check_nginx.sh /etc/keepalived/check_nginx.sh
vi /etc/keepalived/check_nginx.sh #編輯，添加以下代碼
#########################################################
#!/bin/sh
if [ $(ps -C nginx --no-header | wc -l) -eq 0 ]; then
/etc/rc.d/init.d/nginx start
fi
sleep 2
if [ $(ps -C nginx --no-header | wc -l) -eq 0 ]; then
/etc/rc.d/init.d/keepalived stop
fi
#########################################################
:wq! #保存退出
chmod +x /usr/local/keepalived/check_nginx.sh #添加執行權限
七、設置更新虛擬服務器（VIP）地址的arp記錄到網關腳本
touch /usr/local/keepalived/clean_arp.sh
ln -s /usr/local/keepalived/clean_arp.sh /etc/keepalived/clean_arp.sh
vi /etc/keepalived/clean_arp.sh #編輯，添加以下代碼
#!/bin/sh
VIP=$1
GATEWAY=192.168.21.2 #網關地址
/sbin/arping -I eth0 -c 5 -s $VIP $GATEWAY &>/dev/null
:wq! #保存退出
chmod +x /usr/local/keepalived/clean_arp.sh #添加腳本執行權限
service nginx restart #重啓nginx
service keepalived restart #重啓keepalived