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keepalived使用纯C语言写成。软件围绕中心的I/O多路复用器设计提供实时的网络。
它的设计重点是在各个元素之间实现模块化，为了保证稳定性和健壮性，守护进程被分成三个独立的进程。
整体设计基于一个简单的父进程，父进程负责fork并监控子进程。两个子进程，一个负责VRRP框架，
另一个负责健康检查。每个子进程有自己的I/O调度多路复用器，这样可以优化VRRP调度，因为VRRP
调度比健康检查更敏感。另一方面，这个分开的设计使得健康检查机制对外部函数库的使用最小化，
最小化自身的动作并且让主循环空闲来避免自身引起的故障。父进程的监控框架叫做watchdog，
它的设计是：每个子进程打开一个UNIX套接字等待请求，当守护进程启动后，
父进程连接这些UNIX套接字并周期性（5s）地发送hello包到子进程。如果父进程无法发送hello包到远程连接的UNIX套机字，
它会简单地重启子进程。watchdog的设计有两个好处，首先hello包从父进程发送到远程连接的子进程是通过I/O多路复用器调度，
这样它就能够检测子进程调度框架中的死循环。第二个好处是可以使用sysV信号检测子进程是否死掉。
测试当serverA机器重启后，虚IP漂移到serverB充当master角色，就是说serverA重启后不抢占。

一、基础环境
1、角色、ip、版本、内核
masterA 10.1.10.117 3.2.0-4-amd64 7.8 keepaliaved
serverB 10.1.10.185 3.2.0-4-amd64 7.8 keepaliaved

二、安装keepalived
1、apt方式安装keepalived服务(serverA serverB)
apt-get -y install keepalived --force-yes

2、修改master/slave配置(serverA serverB)
1)master 创建keepalived.conf并添加以下内容
cat /etc/keepalived/keepalived.conf 
global_defs
{
router_id aaa
}
vrrp_instance VI_1
{
state BACKUP
interface eth0
virtual_router_id 90
nopreempt
priority 100
advert_int 1
virtual_ipaddress
{
10.1.10.240/24
}
}
2)slave 创建keepalived.conf并添加以下内容
cat /etc/keepalived/keepalived.conf 
global_defs
{
router_id bbb
}
vrrp_instance VI_1
{
state BACKUP
interface eth0
virtual_router_id 90
priority 99
advert_int 1
virtual_ipaddress
{
10.1.10.240/24
}
}
PS:配置说明
state              #MASTER是主服务器，BACKUP是备服务器。
virtual_ipaddress  #设置虚拟IP地址，也叫漂移IP地址。
priority           #值越大优先级越高，主的值在设置上大于备的值
nopreempt          #不抢占(仅配置在state BACKUP时有效 并且这个机器的优先级必须比另一台高)
virtual_router_id  #取值范围是1-255(must be between 1 & 255)
advert_int         #MASTER和BACKUP之间同步检查的时间间隔(s)

3、自定义日志存放地方(不定义的话默认是在/var/log/messages)(serverA serverB)
1)添加以下内容
echo "local3.*                        /var/log/keepalived" >> /etc/rsyslog.conf
2)重启下rsyslog服务
/etc/init.d/rsyslog restart
[ ok ] Stopping enhanced syslogd: rsyslogd.
[ ok ] Starting enhanced syslogd: rsyslogd.

4、启动服务(serverA serverB)
keepalived -d -D -S 3 -f /etc/keepalived/keepalived.conf
PS:启动参数说明
--use-file, -f keepalived.conf_file Use the specified configuration file.
--dump-conf, -d Dump the configuration data.
--log-detail, -D Detailed log messages (the default with the rc script provided).
--log-facility, -S 0-7 Set syslog facility to LOG_LOCAL[0-7] (default=LOG_DAEMON)

5、查看进程(serverA serverB)
ps aux |grep keepalived |grep -v grep
root       2944  0.0  0.3  21984   796 ?        Ss   16:44   0:00 keepalived -d -D -S 3 -f /etc/keepalived/keepalived.conf
root       2945  0.0  0.9  30520  2160 ?        S    16:44   0:00 keepalived -d -D -S 3 -f /etc/keepalived/keepalived.conf
root       2946  0.0  0.6  30396  1468 ?        S    16:44   0:00 keepalived -d -D -S 3 -f /etc/keepalived/keepalived.conf

6、查看相关日志文件(serverA serverB)
ll /var/log/keepalived
-rw-r----- 1 root adm 4215 Sep 22 16:44 /var/log/keepalived

7、查看启动日志(serverA serverB)
1)cat /var/log/keepalived
Sep 22 16:44:12 debian Keepalived: Starting Keepalived v1.2.2 (12/18,2011)
Sep 22 16:44:12 debian Keepalived: Remove a zombie pid file /var/run/keepalived.pid
Sep 22 16:44:12 debian Keepalived: Remove a zombie pid file /var/run/vrrp.pid
Sep 22 16:44:12 debian Keepalived: Remove a zombie pid file /var/run/checkers.pid
Sep 22 16:44:12 debian Keepalived: Starting Healthcheck child process, pid=2945
Sep 22 16:44:12 debian Keepalived: Starting VRRP child process, pid=2946
Sep 22 16:44:12 debian Keepalived_vrrp: Netlink reflector reports IP 10.1.10.117 added
Sep 22 16:44:12 debian Keepalived_vrrp: Netlink reflector reports IP 10.1.10.240 added
Sep 22 16:44:12 debian Keepalived_vrrp: Netlink reflector reports IP fe80::20c:29ff:fec8:87a1 added
Sep 22 16:44:12 debian Keepalived_vrrp: Registering Kernel netlink reflector
Sep 22 16:44:12 debian Keepalived_vrrp: Registering Kernel netlink command channel
Sep 22 16:44:12 debian Keepalived_vrrp: Registering gratutious ARP shared channel
Sep 22 16:44:12 debian Keepalived_healthcheckers: Initializing ipvs 2.6
Sep 22 16:44:12 debian Keepalived_vrrp: Initializing ipvs 2.6
Sep 22 16:44:12 debian Keepalived_vrrp: Opening file '/etc/keepalived/keepalived.conf'.
Sep 22 16:44:12 debian Keepalived_healthcheckers: Netlink reflector reports IP 10.1.10.117 added
Sep 22 16:44:12 debian Keepalived_healthcheckers: Netlink reflector reports IP 10.1.10.240 added
Sep 22 16:44:12 debian Keepalived_healthcheckers: Netlink reflector reports IP fe80::20c:29ff:fec8:87a1 added
Sep 22 16:44:12 debian Keepalived_healthcheckers: Registering Kernel netlink reflector
Sep 22 16:44:12 debian Keepalived_healthcheckers: Registering Kernel netlink command channel
Sep 22 16:44:12 debian Keepalived_healthcheckers: Opening file '/etc/keepalived/keepalived.conf'.
Sep 22 16:44:12 debian Keepalived_vrrp: VRRP is trying to assign invalid VIP {. skipping VIP...
Sep 22 16:44:12 debian Keepalived_vrrp: Configuration is using : 60186 Bytes
Sep 22 16:44:12 debian Keepalived_vrrp: ------< Global definitions >------
Sep 22 16:44:12 debian Keepalived_vrrp:  Router ID = aaa
Sep 22 16:44:12 debian Keepalived_vrrp:  Smtp server connection timeout = 30
Sep 22 16:44:12 debian Keepalived_vrrp:  Email notification from = root@debian
Sep 22 16:44:12 debian Keepalived_vrrp: ------< VRRP Topology >------
Sep 22 16:44:12 debian Keepalived_vrrp:  VRRP Instance = VI_1
Sep 22 16:44:12 debian Keepalived_vrrp:    Want State = MASTER
Sep 22 16:44:12 debian Keepalived_vrrp:    Runing on device = eth0
Sep 22 16:44:12 debian Keepalived_vrrp:    Virtual Router ID = 90
Sep 22 16:44:12 debian Keepalived_vrrp:    Priority = 100
Sep 22 16:44:12 debian Keepalived_vrrp:    Advert interval = 1sec
Sep 22 16:44:12 debian Keepalived_vrrp:    Preempt disabled
Sep 22 16:44:12 debian Keepalived_vrrp:    Virtual IP = 1
Sep 22 16:44:12 debian Keepalived_vrrp:      10.1.10.240/24 dev eth0 scope global
Sep 22 16:44:12 debian Keepalived_vrrp: Using LinkWatch kernel netlink reflector...
Sep 22 16:44:12 debian Keepalived_vrrp: VRRP sockpool: [ifindex(2), proto(112), fd(10,11)]
Sep 22 16:44:12 debian Keepalived_healthcheckers: Configuration is using : 5509 Bytes
Sep 22 16:44:12 debian Keepalived_healthcheckers: ------< Global definitions >------
Sep 22 16:44:12 debian Keepalived_healthcheckers:  Router ID = aaa
Sep 22 16:44:12 debian Keepalived_healthcheckers:  Smtp server connection timeout = 30
Sep 22 16:44:12 debian Keepalived_healthcheckers:  Email notification from = root@debian
Sep 22 16:44:12 debian Keepalived_healthcheckers: ------< SSL definitions >------
Sep 22 16:44:12 debian Keepalived_healthcheckers:  Using autogen SSL context
Sep 22 16:44:12 debian Keepalived_healthcheckers: Using LinkWatch kernel netlink reflector...
Sep 22 16:44:13 debian Keepalived_vrrp: VRRP_Instance(VI_1) Transition to MASTER STATE
Sep 22 16:44:14 debian Keepalived_vrrp: VRRP_Instance(VI_1) Entering MASTER STATE
Sep 22 16:44:14 debian Keepalived_vrrp: VRRP_Instance(VI_1) setting protocol VIPs.
Sep 22 16:44:14 debian Keepalived_vrrp: VRRP_Instance(VI_1) Sending gratuitous ARPs on eth0 for 10.1.10.240
Sep 22 16:44:19 debian Keepalived_vrrp: VRRP_Instance(VI_1) Sending gratuitous ARPs on eth0 for 10.1.10.240
2)cat /var/log/keepalived
Sep 22 16:51:31 debian Keepalived: Starting Keepalived v1.2.2 (12/18,2011)
Sep 22 16:51:31 debian Keepalived: Starting Healthcheck child process, pid=2414
Sep 22 16:51:31 debian Keepalived: Starting VRRP child process, pid=2415
Sep 22 16:51:31 debian Keepalived_vrrp: Netlink reflector reports IP 10.1.10.185 added
Sep 22 16:51:31 debian Keepalived_vrrp: Netlink reflector reports IP fe80::20c:29ff:fe1c:c991 added
Sep 22 16:51:31 debian Keepalived_vrrp: Registering Kernel netlink reflector
Sep 22 16:51:31 debian Keepalived_healthcheckers: Initializing ipvs 2.6
Sep 22 16:51:31 debian Keepalived_vrrp: Registering Kernel netlink command channel
Sep 22 16:51:31 debian Keepalived_vrrp: Registering gratutious ARP shared channel
Sep 22 16:51:31 debian Keepalived_vrrp: Initializing ipvs 2.6
Sep 22 16:51:31 debian Keepalived_healthcheckers: IPVS: Cant initialize ipvs: Protocol not available
Sep 22 16:51:31 debian Keepalived_healthcheckers: Netlink reflector reports IP 10.1.10.185 added
Sep 22 16:51:31 debian Keepalived_healthcheckers: Netlink reflector reports IP fe80::20c:29ff:fe1c:c991 added
Sep 22 16:51:31 debian Keepalived_healthcheckers: Registering Kernel netlink reflector
Sep 22 16:51:31 debian Keepalived_healthcheckers: Registering Kernel netlink command channel
Sep 22 16:51:31 debian Keepalived_healthcheckers: Opening file /etc/keepalived/keepalived.conf.
Sep 22 16:51:31 debian Keepalived_healthcheckers: Configuration is using : 5355 Bytes
Sep 22 16:51:31 debian Keepalived_vrrp: Opening file /etc/keepalived/keepalived.conf.
Sep 22 16:51:31 debian Keepalived_vrrp: VRRP is trying to assign invalid VIP {. skipping VIP...
Sep 22 16:51:31 debian Keepalived_vrrp: Configuration is using : 60164 Bytes
Sep 22 16:51:31 debian Keepalived_vrrp: ------< Global definitions >------
Sep 22 16:51:31 debian Keepalived_vrrp:  Router ID = bbb
Sep 22 16:51:31 debian Keepalived_vrrp:  Smtp server connection timeout = 30
Sep 22 16:51:31 debian Keepalived_vrrp:  Email notification from = root@debian
Sep 22 16:51:31 debian Keepalived_vrrp: ------< VRRP Topology >------
Sep 22 16:51:31 debian Keepalived_vrrp:  VRRP Instance = VI_1
Sep 22 16:51:31 debian Keepalived_vrrp:    Want State = BACKUP
Sep 22 16:51:31 debian Keepalived_vrrp:    Runing on device = eth0
Sep 22 16:51:31 debian Keepalived_vrrp:    Virtual Router ID = 90
Sep 22 16:51:31 debian Keepalived_vrrp:    Priority = 99
Sep 22 16:51:31 debian Keepalived_vrrp:    Advert interval = 1sec
Sep 22 16:51:31 debian Keepalived_vrrp:    Virtual IP = 1
Sep 22 16:51:31 debian Keepalived_vrrp:      10.1.10.240/24 dev eth0 scope global
Sep 22 16:51:31 debian Keepalived_vrrp: Using LinkWatch kernel netlink reflector...
Sep 22 16:51:31 debian Keepalived_vrrp: VRRP_Instance(VI_1) Entering BACKUP STATE
Sep 22 16:51:31 debian Keepalived_vrrp: VRRP sockpool: [ifindex(2), proto(112), fd(11,12)]
Sep 22 16:51:31 debian Keepalived_healthcheckers: ------< Global definitions >------
Sep 22 16:51:31 debian Keepalived_healthcheckers:  Router ID = bbb
Sep 22 16:51:31 debian Keepalived_healthcheckers:  Smtp server connection timeout = 30
Sep 22 16:51:31 debian Keepalived_healthcheckers:  Email notification from = root@debian
Sep 22 16:51:31 debian Keepalived_healthcheckers: ------< SSL definitions >------
Sep 22 16:51:31 debian Keepalived_healthcheckers:  Using autogen SSL context
Sep 22 16:51:31 debian Keepalived_healthcheckers: Using LinkWatch kernel netlink reflector...

8、使用ip命令查看(serverA serverB)
1)使用ip a命令查看
ip a 
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 00:0c:29:c8:87:a1 brd ff:ff:ff:ff:ff:ff
    inet 10.1.10.117/24 brd 10.1.10.255 scope global eth0
    inet 10.1.10.240/24 scope global secondary eth0
    inet6 fe80::20c:29ff:fec8:87a1/64 scope link 
       valid_lft forever preferred_lft forever
2)使用ip a命令查看
ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 00:0c:29:1c:c9:91 brd ff:ff:ff:ff:ff:ff
    inet 10.1.10.185/24 brd 10.1.10.255 scope global eth0
    inet6 fe80::20c:29ff:fe1c:c991/64 scope link 
       valid_lft forever preferred_lft forever       
       
9、删除开机默认启动(serverA serverB)
update-rc.d -f keepalived remove
update-rc.d: using dependency based boot sequencing

10、添加开机启动(serverA serverB)
echo "/usr/sbin/keepalived -d -D -S 3 -f /etc/keepalived/keepalived.conf" >> /etc/rc.local

三、测试
1、直接重启masterA机器
2、在slave上查看IP地址
ip a
lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 00:0c:29:8c:61:6e brd ff:ff:ff:ff:ff:ff
    inet 10.1.10.250/24 brd 10.1.10.255 scope global eth0
    inet 10.1.10.240/24 scope global secondary eth0
    inet6 fe80::20c:29ff:fe8c:616e/64 scope link 
       valid_lft forever preferred_lft forever
3、在slave上查看日志
cat /var/log/keepalived
Sep 22 16:55:00 debian Keepalived_vrrp: VRRP_Instance(VI_1) Transition to MASTER STATE
Sep 22 16:55:01 debian Keepalived_vrrp: VRRP_Instance(VI_1) Entering MASTER STATE
Sep 22 16:55:01 debian Keepalived_vrrp: VRRP_Instance(VI_1) setting protocol VIPs.
Sep 22 16:55:01 debian Keepalived_vrrp: VRRP_Instance(VI_1) Sending gratuitous ARPs on eth0 for 10.1.10.240
Sep 22 16:55:01 debian Keepalived_healthcheckers: Netlink reflector reports IP 10.1.10.240 added
Sep 22 16:55:06 debian Keepalived_vrrp: VRRP_Instance(VI_1) Sending gratuitous ARPs on eth0 for 10.1.10.240
 
四、参考文章
http://www.keepalived.org/