Keepalived基于VRRP协议实现LVS服务的高可用集群，可以利用其来避免单点故障。一个LVS服务会有2台服务器运行Keepalived，一台为主服务器（MASTER），一台为备份服务器（BACKUP），但是对外表现为一个虚拟IP，主服务器会发送特定的消息给备份服务器，当备份服务器收不到这个消息的时候，即主服务器宕机的时候， 备份服务器就会接管虚拟IP，继续提供服务，从而保证了高可用性。Keepalived是VRRP的完美实现，因此在介绍keepalived之前，先介绍一下VRRP的原理。
在现实的网络环境中，两台需要通信的主机大多数情况下并没有直接的物理连接。对于这样的情况，它们之间路由怎样选择？主机如何选定到达目的主机的下一跳路由，这个问题通常的解决方法有二种：
在主机上使用动态路由协议(RIP、OSPF等)
在主机上配置静态路由
很明显，在主机上配置动态路由是非常不切实际的，因为管理、维护成本以及是否支持等诸多问题。配置静态路由就变得十分流行，但路由器(或者说默认网关default gateway)却经常成为单点故障。VRRP的目的就是为了解决静态路由单点故障问题，VRRP通过一竞选(election)协议来动态的将路由任务交给LAN中虚拟路由器中的某台VRRP路由器。
VRRP（Virtual Router Redundancy Protocol，虚拟路由冗余协议）是一种容错协议
在一个VRRP虚拟路由器中，包含多台物理路由器，但是这多台的物理的器并不能同时工作，而是由一台称为MASTER的负责路由工作，其它的都是BACKUP，MASTER并非一成不变，VRRP让每个VRRP路由器参与竞选，最终获胜的就是MASTER。MASTER拥有一些特权，比如，拥有虚拟路由器的IP地址，我们的主机就是用这个IP地址作为静态路由的。拥有特权的MASTER要负责转发发送给网关地址的包和响应ARP请求。
VRRP通过竞选协议来实现虚拟路由器的功能，所有的协议报文都是通过IP多播(multicast)包(多播地址224.0.0.18)形式发送的。虚拟路由器由VRID(范围0-255)和一组IP地址组成，对外表现为一个相同的MAC地址。
所以，在一个虚拟路由 器中，不管谁是MASTER，对外都是相同的MAC（会进行arp欺骗）和IP(称之为VIP)。客户端主机并不需要因为MASTER的改变而修改自己的路由配置，对客户端来说，这种主从的切换是隐藏的。
在一个虚拟路由器中，只有作为MASTER的VRRP路由器会一直发送VRRP通告信息(VRRPAdvertisement message)，BACKUP不会抢占MASTER，除非它的优先级(priority)更高。当MASTER不可用时(BACKUP收不到通告信息)， 多台BACKUP中优先级最高的这台会被抢占为MASTER。这种抢占是非常快速的(<1s)，以保证服务的连续性。由于安全性考虑，VRRP包使用了加密协议进行加密。
下面将开始用Keepalived+lvS构建一个Web高可用集群
node1:192.168.139.2 主DR_Server
node2:192.168.139.4 备DR_server
node4:192.168.139.8 RS1_Server
node5:192.168.139.9 RS2_Server
node1,node2装keepalived,ipvsadm
node4,node5装httpd
因为每个节点都有VIP，但进行ARP响应时必须只能有Director上的VIP响应（要是VIP所在网卡都响应ARP广播就乱了，因为每个节点都有VIP），所以RS上的VIP必须隐藏起来让其不进行ARP响应。为了让RS上的VIP隐藏起来，必须对RS进行如下设置
echo 2 > /proc/sys/net/ipv4/conf/lo/arp_announce
echo 2 > /proc/sys/net/ipv4/conf/all/arp_announce
echo 1 > /proc/sys/net/ipv4/conf/lo/arp_ignore
cho 1 > /proc/sys/net/ipv4/conf/all/arp_ignore
直接用下面的脚本设置RS_Server的环境，更详细的LVS_DR模式介绍请看：
http://11107124.blog.51cto.com/11097124/1867364
[[email protected] sh]# vim rs.sh
#!/bin/bash
#
VIP=192.168.139.100
STATUS() {
if [ -e /var/lock/subsys/ipvs_lock ] ;then
echo -e "\033[40;31m initial OK \033[0m "
else
echo -e "\033[40;31m initial not ok \033[0m "
fi
}
case $1 in
start)
/sbin/ifconfig lo down
/sbin/ifconfig lo up
echo 1 > /proc/sys/net/ipv4/conf/lo/arp_ignore
echo 1 > /proc/sys/net/ipv4/conf/all/arp_ignore
echo 2 > /proc/sys/net/ipv4/conf/lo/arp_announce
echo 2 > /proc/sys/net/ipv4/conf/all/arp_announce
/sbin/ifconfig lo:0 $VIP broadcast $VIP netmask 255.255.255.255 up
/sbin/route add -host $VIP dev lo:0
/bin/touch /var/lock/subsys/ipvs_lock
;;
stop)
/sbin/ifconfig lo:0 down
/sbin/route del $VIP &> /dev/null
echo 0 > /proc/sys/net/ipv4/conf/lo/arp_ignore
echo 0 > /proc/sys/net/ipv4/conf/all/arp_ignore
echo 0 > /proc/sys/net/ipv4/conf/lo/arp_announce
echo 0 > /proc/sys/net/ipv4/conf/all/arp_announce
/bin/rm -f /var/lock/subsys/ipvs_lock
status)
STATUS;;
*)
echo "Usage: `basename $0` START|STOP"
exit 7
esac
node4，node5执行此脚本，设置LVS_DR模式的准备环境
[[email protected] keepalived]# chmod +x notify.sh
[[email protected] sh]# bash rs.sh start
[[email protected] sh]# bash rs.sh start
[[email protected] sh]# ifconfig
eth0 inet addr:192.168.139.8 Bcast:192.168.139.255 Mask:255.255.255.0
lo inet addr:127.0.01 Mask:255.0.0.0
lo:0 inet addr:192.168.139.6 Mask:255.255.255.255
[[email protected] sh]# route -n
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.139.6 0.0.0.0 255.255.255.255 UH 0 0 0 lo
[[email protected] ~]# service httpd start
[[email protected] ~]# service httpd start
[[email protected] sh]# netstat -tnlp |grep 80
tcp 0 0 :::80 :::* LISTEN 3047/httpd
至此RS1，RS2已经准备好，node1和node2装软件
[[email protected] ~]# yum install keepalived ipvsadm -y
[[email protected] mail]# yum install keepalived ipvsadm -y
[[email protected] ~]# cd /etc/keepalived/
编辑之前最好先备份
[[email protected] keepalived]# cp keepalived.conf keepalived.conf.bak
[[email protected] keepalived]# vim keepalived.conf
! Configuration File for keepalived
global_defs { 此段定义全局默认配置
notification_email {
[email protected] #写入你的邮件地址，出现故障给你发邮件
}
notification_email_from [email protected]#邮件由本地谁发出
smtp_server 127.0.0.1 #本地smtp-server
smtp_connect_timeout 30 #smtp连接超时时间
router_id LVS_DEVEL
}
vrrp_instance VI_1 {
state MASTER #当前节点为主节点
interface eth0 #通告信息及虚拟路由工作的网卡接口
virtual_router_id 51 #要与备份节点上ID一样
priority 101 #优先级为101，要比备份节点的大
advert_int 1 #每隔一秒发一次通告信息
authentication {
auth_type PASS #pass为简单字符认证，发送的通告信息要认证通过才接受通过信息
auth_pass keepalived #随便给个字符串
}
virtual_ipaddress {
192.168.139.100/24 dev eth0 label eth0:0
#VIP/掩码 设备 标签
}
}
virtual_server 192.168.139.100 80 { 此段定义DR_Server
delay_loop 6
lb_algo wrr #DR算法为wrr
lb_kind DR #lvs类型为DR
nat_mask 255.255.255.0 #网络掩码
# persistence_timeout 50 #持久连接时间，本实验不用
protocol TCP #协议为TCP
real_server 192.168.139.8 80 { 本段定义RS_Server
weight 2 #192.168.139.8节点权重为2
HTTP_GET { #对http协议做健康状态检查
url {
path /
status_code 200 #如果正常，状态码返回200
}
connect_timeout 2 #连接超时2S
nb_get_retry 3 #重试此时为3
delay_before_retry 1 #每次重试隔1S
}
}
real_server 192.168.139.9 80 {
weight 1
HTTP_GET {
url {
path /
status_code 200
}
connect_timeout 2
nb_get_retry 3
delay_before_retry 1
}
}
}
更多详细参数,请man
[[email protected] keepalived]# man keepalived.conf
复制到node2
[[email protected] keepalived]#scp keepalived.conf node2:/etc/keepalived/
[[email protected] keepalived]# vim keepalived.conf
改 MASTER->BACKUP
priority 101->100
weight 1->2 （如果是rr算法，权重就没用）
[[email protected] keepalived]# service keepalived start
[[email protected] keepalived]# service keepalived start
[[email protected] keepalived]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0C:29:1C:13:12
inet addr:192.168.139.2 Bcast:192.168.139.255 Mask:255.255.255.0
eth0:0 Link encap:Ethernet HWaddr 00:0C:29:1C:13:12
inet addr:192.168.139.100 Bcast:0.0.0.0 Mask:255.255.255.0
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
[[email protected] keepalived]# ipvsadm -l -n
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
-> RemoteAddress:Port Forward Weight ActiveConn InActConn
TCP 192.168.139.100:80 wrr
-> 192.168.139.8:80 Route 1 0 0
-> 192.168.139.9:80 Route 1 0 0
浏览器测试：
刷新
集群工作正常
[[email protected] sh]# service httpd stop
停掉一个节点服务，则会立马有邮件通知给管理员node4节点DOWN了
[[email protected] keepalived]# mail
>N 17 [email protected] Thu Dec 22 17:54 17/625 "[LVS_DEVEL] Realserver [192.168.139.8]:80 - DOWN"
&
Message 17:
From [email protected] Thu Dec 22 17:54:32 2016
Return-Path: <[email protected]>
X-Original-To: [email protected]
Delivered-To: [email protected]
Date: Thu, 22 Dec 2016 09:54:32 +0000
From: [email protected]
Subject: [LVS_DEVEL] Realserver [192.168.139.8]:80 - DOWN
X-Mailer: Keepalived
To: [email protected]
Status: R
=> CHECK failed on service : connection error <=
node5节点被移除了
[[email protected] keepalived]# ipvsadm -l -n
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
-> RemoteAddress:Port Forward Weight ActiveConn InActConn
TCP 192.168.139.100:80 wrr
-> 192.168.139.9:80 Route 1 0 0
[[email protected] sh]# service httpd start
node5节点又被加入了集群
[[email protected] keepalived]# ipvsadm -l -n
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
-> RemoteAddress:Port Forward Weight ActiveConn InActConn
TCP 192.168.139.100:80 wrr
-> 192.168.139.8:80 Route 1 0 0
-> 192.168.139.9:80 Route 1 0 0
但是万一两个RS都挂掉怎么办？
在node1和node2上装httpd（因为VIP可能会在两个节点转移，所两个节点都要装），将其做成fall_back_server，一旦两个RS挂掉，则提供一个临时页面，通知用户
node1 node2都进行如下操作
[[email protected] keepalived]# yum install httpd -y
[[email protected] ~]# vim /var/www/html/index.html
<h1>服务器维护中</h1>
[[email protected] ~]# service httpd start
[[email protected] keepalived]# vim keepalived.conf
在virtual_server中加入 sorry_server 127.0.0.1 80
[[email protected] keepalived]# service keepalived restart
[[email protected] keepalived]# service keepalived restart
[[email protected] sh]# service httpd stop
[[email protected] ~]# service httpd stop
可以看到Local 127.0.0.1上线
[[email protected] keepalived]# ipvsadm -l -n
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
-> RemoteAddress:Port Forward Weight ActiveConn InActConn
TCP 192.168.139.100:80 wrr
-> 127.0.0.1:80 Local 1 0 0
浏览器测试，node4 node5都挂了后由运行有VIP的DR提供维护页面
[[email protected] sh]# service httpd start
只要有一个RS在线，Local server就会下线
[[email protected] keepalived]# ipvsadm -l -n
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
-> RemoteAddress:Port Forward Weight ActiveConn InActConn
TCP 192.168.139.100:80 wrr
-> 192.168.139.8:80 Route 1 1 0
[[email protected] ~]# service httpd start
写一个检测脚本，完成DR的切换，直接编辑文件
[[email protected] ~]# vim /etc/keepalived/keepalived.conf
vrrp_script chk_down { 定义一个叫chk_down的脚本检查DR_Server
script "[ -e /etc/keepalived/down ] && exit 1 || exit 0 " \\当/etc/keepalived/down \\ 文件存在时则检查失败，否则成功（只有返回值为0，才表示成 \\功）,次数还可以通过文件设置复杂检测脚本，而不止一个命令
interval 2 \\每隔2秒监测一次
weight -2 \\如果监测为失败则此节点priority减去2（如node1由101变成99小于node2 \\的100则变为备节点）
fall 2 \\只有连续监测两次都失败才证明此DR真的挂了
rise 1 \\只要有一次监测成功则此DR没有挂
}
vrrp_instance VI_1 {
state MASTER
interface eth0
virtual_router_id 51
priority 101
advert_int 1
authentication {
auth_type PASS
auth_pass keepalived
}
virtual_ipaddress {
192.168.139.100/24 dev eth0 label eth0:0
}
track_script {
chk_down \\这里定义执行上面写的chk_down脚本
}
}
编辑node2，重启服务
[[email protected] ~]# vim /etc/keepalived/keepalived.conf
[[email protected] ~]# service keepalived restart
[[email protected] ~]# service keepalived restart
[[email protected] ~]# cd /etc/keepalived/
创建down文件从node1转移到node2，node1变成备节点
[[email protected] keepalived]# touch down
[[email protected] keepalived]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0C:29:1C:13:12
inet addr:192.168.139.2 Bcast:192.168.139.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fe1c:1312/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:18158 errors:0 dropped:0 overruns:0 frame:0
TX packets:18798 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:3011063 (2.8 MiB) TX bytes:3830969 (3.6 MiB)
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:155 errors:0 dropped:0 overruns:0 frame:0
TX packets:155 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:11194 (10.9 KiB) TX bytes:11194 (10.9 KiB)
可以看到eth0:0（VIP）从本机转移了，查看一下日志描述
[[email protected] keepalived]# tail /var/log/messages
Dec 22 18:31:43 node1 Keepalived_vrrp[2107]: VRRP_Script(chk_down) failed
检测失败
Dec 22 18:31:44 node1 Keepalived_vrrp[2107]: VRRP_Instance(VI_1) Received higher prio advert
收到更高的优先级（node1优先级由101-2=99小于node2的100）
Dec 22 18:31:44 node1 Keepalived_vrrp[2107]: VRRP_Instance(VI_1) Entering BACKUP STATE
node1转换为备节点
Dec 22 18:31:44 node1 Keepalived_vrrp[2107]: VRRP_Instance(VI_1) removing protocol VIPs.
移除VIP
Dec 22 18:31:44 node1 Keepalived_healthcheckers[2106]: Netlink reflector reports IP 192.168.139.100 removed
VIP在node2已经设置
[[email protected] ~]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0C:29:5F:68:2F
inet addr:192.168.139.4 Bcast:192.168.139.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fe5f:682f/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:21023 errors:0 dropped:0 overruns:0 frame:0
TX packets:20015 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:3081886 (2.9 MiB) TX bytes:2313640 (2.2 MiB)
eth0:0 Link encap:Ethernet HWaddr 00:0C:29:5F:68:2F
inet addr:192.168.139.100 Bcast:0.0.0.0 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
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:226 errors:0 dropped:0 overruns:0 frame:0
TX packets:226 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:21401 (20.8 KiB) TX bytes:21401 (20.8 KiB)
[[email protected] ~]# tail /var/log/messages
Dec 22 18:30:42 node2 Keepalived_vrrp[5295]: VRRP_Script(chk_down) succeeded
检测成功
Dec 22 18:31:47 node2 Keepalived_vrrp[5295]: VRRP_Instance(VI_1) Transition to MASTER STATE
转换为主节点
Dec 22 18:31:48 node2 Keepalived_vrrp[5295]: VRRP_Instance(VI_1) setting protocol VIPs.
设置VIP
Dec 22 18:31:48 node2 Keepalived_healthcheckers[5294]: Netlink reflector reports IP 192.168.139.100 added
VIP添加成功
Dec 22 18:31:48 node2 Keepalived_vrrp[5295]: VRRP_Instance(VI_1) Sending gratuitous ARPs on eth0 for 192.168.139.100
node2节点进行ARP欺骗（因为前端交换机与DR_Server通信是建立在MAC地址上的，而DR现在由node1变成了node2,所以交互机上原来的MAC表失效，交换机不能通过MAC表连接到VIP，所以node2就进行了一个ARP欺骗，自问自答，伪造了node1的MAC，从而实现了前端交换机照样可以根据原来的MAC表VIP（node2））
这样就能实现DR_Server 的转移
当Vrrp事物变化时，如何发送警告邮件给指定的管理员？
写脚本控制邮件的发送
脚本内容如下
[[email protected] keepalived]# vim notify.sh
#!/bin/bash
#
contact=‘[email protected]‘
Usage() { \\定义的一个Usage函数
echo "Usage:`basename $0` {master|backup|fault} VIP"
}
Notify() {
subject="`hostname`‘s state changed to $1" \\邮件主题
mailbody="`date "+%F %T"`: `hostname`‘s state change to $1,$VIP floating." \\邮件内容
echo $mailbody |mail -s "$subject" $contact \\发送邮件
}
[ $# -lt 2 ] && Usage && exit \\参数小于2时执行Usage函数并退出
VIP=$2 \\VIP为第二个参数
case $1 in
master)
Notify master \\第一个参数是master时，调用Notify函数
;;
backup)
Notify backup
;;
fault)
Notify fault
;;
*)
Usage
exit 1
;;
esac
[[email protected] keepalived]# chmod +x notify.sh
两个节点重启sendmail和keepalived
[[email protected] keepalived]# service keepalived restart
[[email protected] keepalived]# service sendmail restart
[[email protected] keepalived]# service keepalived restart
[[email protected] keepalived]# service sendmail restart
删除创建的down文件，进行DR切换
[[email protected] keepalived]# rm -rf down
[[email protected] keepalived]# mail
25 root Thu Dec 22 19:30 23/896 "node1.zxl.com‘s state changed to backup"
& 25
Message 25:
From [email protected] Thu Dec 22 19:30:36 2016
Return-Path: <[email protected]>
X-Original-To: [email protected]
Delivered-To: [email protected]
From: root <[email protected]>
Date: Thu, 22 Dec 2016 19:30:36 +0800
To: [email protected]
Subject: node1.zxl.com‘s state changed to backup
User-Agent: Heirloom mailx 12.4 7/29/08
Content-Type: text/plain; charset=us-ascii
Status: RO
2016-12-22 19:30:36: node1.zxl.com‘s state change to backup,192.168.139.100 floating.
VIP转移发送的邮件已经收到
本次实验完毕！