负载平衡是一种在真实服务器集群中分配IP流量的方法,可提供一个或多个高度可用的虚拟服务。在设计负载均衡拓扑时,重要的是要考虑负载均衡器本身的可用性以及它背后的真实服务器。用C编写的类似于layer3, 4 & 7交换机制软件,具备我们平时说的第3层、第4层和第7层交换机的功能。
Keepalived为负载平衡和高可用性提供了框架。负载平衡框架依赖于众所周知且广泛使用的Linux虚拟服务器(IPVS)内核模块,该模块提供第4层负载平衡。Keepalived实现了一组健康检查器,以根据其健康动态地自适应地维护和管理负载平衡的服务器池。虚拟冗余路由协议(VRRP)实现高可用性。VRRP是路由器故障转移的基础砖块。此外,keepalived实现了一组挂钩到VRRP有限状态机,提供低级别和高速协议交互。每个Keepalived框架可以独立使用或一起使用,以提供弹性基础设施。
在这种情况下,负载平衡器也可以被称为导向器或LVS路由器。
简而言之,Keepalived提供了两个主要功能:
Keepalived使用四个Linux内核组件:
上图是Keepalived的功能体系结构,大致分两层:用户空间(user space)和内核空间(kernel space)。 内核空间:主要包括IPVS(IP虚拟服务器,用于实现网络服务的负载均衡)和NETLINK(提供高级路由及其他相关的网络功能)两个部份。 用户空间:
Keepalived的所有功能是配置keepalived.conf文件来实现的。
2.1 方法一:yum方式
1、yum安装
安装依赖包
[root@localhost ~]# yum install -y curl gcc openssl-devel libnl3-devel net-snmp-devel
[root@localhost ~]# yum install -y keepalived
2、初始化及启动
[root@localhost ~]# systemctl start keepalived //启动keepalived
[root@localhost ~]# systemctl enable keepalived //加入开机启动keepalived
[root@localhost ~]# systemctl restart keepalived //重新启动keepalived
[root@localhost ~]# systemctl status keepalived //查看keepalived状态
1、官网下载keepalived的最新版本,解压并安装
[root@master src]# pwd
/usr/local/src
[root@master src]# wget http://www.keepalived.org/software/keepalived-2.0.7.tar.gz
[root@master src]# tar xvf keepalived-2.0.7.tar.gz
[root@master src]# cd keepalived-2.0.7
[root@master keepalived-2.0.7]# ./configure --prefix=/usr/local/keepalived
[root@master keepalived-2.0.7]# make && make install
完成后会在以下路径生成:
/usr/local/etc/keepalived/keepalived.conf
/usr/local/etc/sysconfig/keepalived
/usr/local/sbin/keepalived
2、初始化及启动
# keepalived启动脚本变量引用文件,默认文件路径是/etc/sysconfig/,也可以不做软链接,直接修改启动脚本中文件路径即可(安装目录下)
[root@localhost /]# cp /usr/local/keepalived/etc/sysconfig/keepalived /etc/sysconfig/keepalived
# 将keepalived主程序加入到环境变量(安装目录下)
[root@localhost /]# cp /usr/local/keepalived/sbin/keepalived /usr/sbin/keepalived
# keepalived启动脚本(源码目录下),放到/etc/init.d/目录下就可以使用service命令便捷调用
[root@localhost /]# cp /usr/local/src/keepalived-2.0.7/keepalived/etc/init.d/keepalived /etc/init.d/keepalived
# 将配置文件放到默认路径下
[root@localhost /]# mkdir /etc/keepalived
[root@localhost /]# cp /usr/local/keepalived/etc/keepalived/keepalived.conf /etc/keepalived/keepalived.conf
keepalived服务安装完成之后,后面的主要工作就是在keepalived.conf文件中配置HA和负载均衡。一个功能比较完整的常用的keepalived配置文件,主要包含三块:全局定义块、VRRP实例定义块和虚拟服务器定义块。全局定义块是必须的,如果keepalived只用来做ha,虚拟服务器是可选的。下面是一个功能比较完整的配置文件模板:
#全局定义块
global_defs {
# 邮件通知配置
notification_email {
email1
email2
}
notification_email_from email
smtp_server host
smtp_connect_timeout num
lvs_id string
router_id string ## 标识本节点的字条串,通常为hostname
}
#VRRP 实例定义块
vrrp_sync_group string {
group {
string
string
}
}
vrrp_instance string {
state MASTER|BACKUP
virtual_router_id num
interface string
mcast_src_ip @IP
priority num
advert_int num
nopreempt
smtp_alert
lvs_sync_daemon_interface string
authentication {
auth_type PASS|AH
auth_pass string
}
virtual_ipaddress { # Block limited to 20 IP addresses @IP
@IP
@IP
}
}
#虚拟服务器定义块
virtual_server (@IP PORT)|(fwmark num) {
delay_loop num
lb_algo rr|wrr|lc|wlc|sh|dh|lblc
lb_kind NAT|DR|TUN
persistence_timeout num
protocol TCP|UDP
real_server @IP PORT {
weight num
notify_down /path/script.sh
TCP_CHECK {
connect_port num
connect_timeout num
}
}
real_server @IP PORT {
weight num
MISC_CHECK {
misc_path /path_to_script/script.sh(or misc_path “/path_to_script/script.sh <arg_list>”)
}
}
real_server @IP PORT {
weight num
HTTP_GET|SSL_GET {
url {
# You can add multiple url block path alphanum
digest alphanum
}
connect_port num
connect_timeout num
nb_get_retry num
delay_before_retry num
}
}
}
1、email通知(notification_email、smtp_server、smtp_connect_timeout):用于服务有故障时发送邮件报警,可选项,不建议用。需要系统开启sendmail服务,建议用第三独立监控服务,如用nagios全面监控代替。 2、lvs_id:lvs负载均衡器标识,在一个网络内,它的值应该是唯一的。 3、router_id:用户标识本节点的名称,通常为hostname 4、花括号{}:用来分隔定义块,必须成对出现。如果写漏了,keepalived运行时不会得到预期的结果。由于定义块存在嵌套关系,因此很容易遗漏结尾处的花括号,这点需要特别注意。