原文：http://blog.chinaunix.net/uid-20639775-id-154518.html
一、爲什麼要使用負載均衡技術？
1、系統高可用性
2、 系統可擴展性
3、 負載均衡能力
LVS+keepalived能很好的實現以上的要求，LVS提供負載均衡，keepalived提供健康檢查，故障轉移，提高系統的可用性！採用這樣的架構以後很容易對現有系統進行擴展，只要在後端添加或者減少realserver，只要更改lvs的配置文件，並能實現無縫配置變更！
二、LVS+Keepalived介紹
1、 LVS
LVS是一個開源的軟件，可以實現LINUX平臺下的簡單負載均衡。LVS是Linux Virtual Server的縮寫，意思是Linux虛擬服務器。目前有三種IP負載均衡技術（VS/NAT、VS/TUN和VS/DR）；八種調度算法（rr,wrr,lc,wlc,lblc,lblcr,dh,sh）。
2、 keepalived
Keepalived 是運行在lvs 之上，它的主要功能是實現真實機的故障隔離及負載均衡器間的失敗切換，提高系統的可用性
三、LVS+keepalived負載均衡架構圖
四、LVS+keepalived的安裝和配置
1. 配置環境
System OS：CentOS release 5.4
Software：ipvsadm-1.24.tar.gz, keepalived-1.1.19.tar.gz
2. 信息列表
名稱 | IP |
LVS-Master | 192.168.1.112 |
LVS-BACKUP | 192.168.1.113 |
LVS-VIP | 192.168.1.115 |
Realserver1 | 192.168.1.105 |
Realserver2 | 192.168.1.103 |
Realserver3 | 192.168.1.104 |
3. 安裝lvs
分別在backup lvs和master lvs上安裝
wget http://www.linuxvirtualserver.org/software/kernel-2.6/ipvsadm-1.24.tar.gz
ln -s /usr/src/kernels/2.6.18-164.el5-i686/ /usr/src/linux
tar zxvf ipvsadm-1.24.tar.gz
cd ipvsadm-1.24
make && make install
4. 安裝keepalived
分別在backup lvs和master lvs上安裝
wget http://www.keepalived.org/software/keepalived-1.1.19.tar.gz
tar zxvf keepalived-1.1.19.tar.gz
cd keepalived-1.1.19
./configure --prefix=/usr/local/keepalived
make
make install
cp /usr/local/keepalived/sbin/keepalived /usr/sbin/
cp /usr/local/keepalived/etc/sysconfig/keepalived /etc/sysconfig/
cp /usr/local/keepalived/etc/rc.d/init.d/keepalived /etc/init.d/
mkdir /etc/keepalived
5. 配置keepadlived
LVS-Master的配置文件如下
[root@linux5 ~]# cat /etc/keepalived/keepalived.conf
global_defs {
notification_email {
[email protected] #email 通知
}
notification_email_from [email protected]
smtp_server 127.0.0.1
smtp_connect_timeout 30
router_id LVS1 #設置lvs的id，在一個網絡內應該是唯一的
}
vrrp_sync_group test { #設置vrrp組
group {
loadbalance
}
}
vrrp_instance loadbalance {
state MASTER #設置lvs的狀態，報錯MASTER和BACKUP兩種，必須大寫
interface eth0 #設置對外服務的接口
lvs_sync_daemon_inteface eth0 #設置lvs監聽的接口
virtual_router_id 51 #設置虛擬路由表示
priority 180 #設置優先級，數值越大，優先級越高
advert_int 5 #設置同步時間間隔
authentication { #設置驗證類型和密碼
auth_type PASS
auth_pass 1111
}
virtual_ipaddress { #設置lvs vip
192.168.1.115
}
}
virtual_server 192.168.1.115 80 {
delay_loop 6 #健康檢查時間間隔
lb_algo rr #負載均衡調度算法
lb_kind DR #負載均衡轉發規則
#persistence_timeout 20 #設置會話保持時間，對bbs等很有用
protocol TCP #協議
real_server 192.168.1.105 80 {
weight 3 #設置權重
TCP_CHECK {
connect_timeout 3
nb_get_retry 3
delay_before_retry 3
connect_port 80
}
}
real_server 192.168.1.103 80 {
weight 3
TCP_CHECK {
connect_timeout 3
nb_get_retry 3
delay_before_retry 3
connect_port 80
}
}
real_server 192.168.1.104 80 {
weight 3
TCP_CHECK {
connect_timeout 3
nb_get_retry 3
delay_before_retry 3
connect_port 80
}
}
}
LVS-backup的配置文件如下
global_defs {
notification_email {
}
notification_email_from [email protected]
smtp_server 127.0.0.1
smtp_connect_timeout 30
router_id LVS2
}
vrrp_sync_group test {
group {
loadbalance
}
}
vrrp_instance loadbalance {
state BACKUP
interface eth0
lvs_sync_daemon_inteface eth0
virtual_router_id 51
priority 150
advert_int 5
authentication {
auth_type PASS
auth_pass 1111
}
virtual_ipaddress {
192.168.1.115
}
}
virtual_server 192.168.1.115 80 {
delay_loop 6
lb_algo rr
lb_kind DR
#persistence_timeout 20
protocol TCP
real_server 192.168.1.105 80 {
weight 3
TCP_CHECK {
connect_timeout 3
nb_get_retry 3
delay_before_retry 3
connect_port 80
}
}
real_server 192.168.1.103 80 {
weight 3
TCP_CHECK {
connect_timeout 3
nb_get_retry 3
delay_before_retry 3
connect_port 80
}
}
real_server 192.168.1.104 80 {
weight 3
TCP_CHECK {
connect_timeout 3
nb_get_retry 3
delay_before_retry 3
connect_port 80
}
}
}
6. Realserver的配置
三臺客戶端的腳本都一樣！
cat /etc/rc.d/init.d/realserver.sh
#!/bin/bash
# description: Config realserver lo and apply noarp
SNS_VIP=192.168.1.115
/etc/rc.d/init.d/functions
case "$1" in
start)
ifconfig lo:0 $SNS_VIP netmask 255.255.255.255 broadcast $SNS_VIP
/sbin/route add -host $SNS_VIP dev lo:0
echo "1" >/proc/sys/net/ipv4/conf/lo/arp_ignore
echo "2" >/proc/sys/net/ipv4/conf/lo/arp_announce
echo "1" >/proc/sys/net/ipv4/conf/all/arp_ignore
echo "2" >/proc/sys/net/ipv4/conf/all/arp_announce
sysctl -p >/dev/null 2>&1
echo "RealServer Start OK"
;;
stop)
ifconfig lo:0 down
route del $SNS_VIP >/dev/null 2>&1
echo "0" >/proc/sys/net/ipv4/conf/lo/arp_ignore
echo "0" >/proc/sys/net/ipv4/conf/lo/arp_announce
echo "0" >/proc/sys/net/ipv4/conf/all/arp_ignore
echo "0" >/proc/sys/net/ipv4/conf/all/arp_announce
echo "RealServer Stoped"
;;
*)
echo "Usage: $0 {start|stop}"
exit 1
esac
exit 0
7. 測試
1) 首先測試各個readserver，確定各個readserver都能正常訪問，測試realserver.sh腳本，看啓動後能不能綁定lvs vip，停止後能不能去除綁定的vip
2) 測試lvs能否進行負載均衡轉發，利用ipvsadm命令查看，如果想只當當前的請求轉發到哪個服務器去了，可以用ipvsadm加選項來查看，其完整形式爲：ipvsadm –lcn | grep 192.168.1.115
3) 停掉主lvs看lvs backup是否接管！
4) 更詳細信息請查看日誌，tail -f /var/log/messages