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@localhost src]# pwd
/usr/local/src
[root@localhost src]# wget http://www.keepalived.org/software/keepalived-2.0.13.tar.gz
[root@localhost src]# tar xvf keepalived-2.0.13.tar.gz
[root@localhost src]# cd keepalived-2.0.13
[root@localhostr keepalived-2.0.13]# ./configure --prefix=/usr/local/keepalived
1. 系统出现警告信息“*** WARNING - this build will not support IPVS with IPv6. Please install libnl/libnl-3 dev libraries to support IPv6 with IPVS.”，具体日志如下：
Keepalived configuration ------------------------ Keepalived version : 2.0.13 Compiler : gcc Preprocessor flags : Compiler flags : -Wall -Wunused -Wstrict-prototypes -Wextra -g -O2 Linker flags : Extra Lib : -lcrypto -lssl Use IPVS Framework : Yes IPVS use libnl : No IPVS syncd attributes : No IPVS 64 bit stats : No fwmark socket support : Yes Use VRRP Framework : Yes Use VRRP VMAC : Yes Use VRRP authentication : Yes With ip rules/routes : Yes SNMP vrrp support : No SNMP checker support : No SNMP RFCv2 support : No SNMP RFCv3 support : No DBUS support : No SHA1 support : No Use Debug flags : No Stacktrace support : No Memory alloc check : No libnl version : None Use IPv4 devconf : No Use libiptc : No Use libipset : No init type : upstart Build genhash : Yes Build documentation : No *** WARNING - this build will not support IPVS with IPv6. Please install libnl/libnl-3 dev libraries to support IPv6 with IPVS.
解决方案一：（在线安装）
执行yum命令yum -y install libnl libnl-devel解决上述警告问题
[root@localhost keepalived-2.0.13]# yum -y install libnl libnl-devel
解决方案二：（离线安装）
离线安装libnl-devel包，从网上下载libnl-devel-1.1.4-2.el6.x86_64.rpm包，执行rpm -ivh libnl-devel-1.1.4-2.el6.x86_64.rpm命令。
[root@localhost other-packages]# wget http://mirror.centos.org/centos/6/os/x86_64/Packages/libnl-devel-1.1.4-2.el6.x86_64.rpm ####执行wget命令是从另外一台可以连接外网的服务器上下载libnl-devel-1.1.4-2.el6.x86_64.rpm包的命令，可以忽略，只是为大家提供个下载libnl-devel地址#### [root@localhost other-packages]# rpm -ivh libnl-devel-1.1.4-2.el6.x86_64.rpm Preparing... ########################################### [100%] package libnl-devel-1.1.4-2.el6.x86_64 is already installed
安装完成以后，重新执行configure命令
[root@localhost keepalived-2.0.13]# ./configure --prefix=/usr/local/keepalived
2. 系统出现错误信息“configure: error: libnfnetlink headers missing”，具体日志如下：
checking for nl_socket_modify_cb in -lnl... yes checking for linux/rtnetlink.h... yes checking libnfnetlink/libnfnetlink.h usability... no checking libnfnetlink/libnfnetlink.h presence... no checking for libnfnetlink/libnfnetlink.h... no configure: error: libnfnetlink headers missing
解决方案一：（在线安装）
执行yum命令yum install -y libnfnetlink-devel解决上述错误问题
[root@localhost keepalived-2.0.13]# yum install -y libnfnetlink-devel
解决方案二：（离线安装）
Linux执行wget下载rpm包（离线安装libnfnetlink包时所需rpm包，执行wget下载libnfnetlink rpm包命令，此步可以忽略，只是为大家提供个下载libnfnetlink地址），具体命令如下：
wget ftp://mirror.switch.ch/mirror/centos/6/os/x86_64/Packages/libnfnetlink-1.0.0-1.el6.x86_64.rpm wget ftp://mirror.switch.ch/mirror/centos/6/os/x86_64/Packages/libnfnetlink-devel-1.0.0-1.el6.x86_64.rpm
执行rpm -ivh libnfnetlink-1.0.0-1.el6.x86_64.rpm命令安装libnfnetlink-1.0.0-1.el6.x86_64.rpm包，具体如下：
[root@localhost other-packages]# rpm -ivh libnfnetlink-1.0.0-1.el6.x86_64.rpm Preparing... ########################################### [100%] 1:libnfnetlink ########################################### [100%]
执行rpm -ivh libnfnetlink-devel-1.0.0-1.el6.x86_64.rpm命令安装libnfnetlink-devel-1.0.0-1.el6.x86_64.rpm包，具体如下：
[root@localhost other-packages]# rpm -ivh libnfnetlink-devel-1.0.0-1.el6.x86_64.rpm Preparing... ########################################### [100%] 1:libnfnetlink-devel ########################################### [100%]
安装完成以后，重新执行configure命令
[root@localhost keepalived-2.0.13]# ./configure --prefix=/usr/local/keepalived
3. 编译keepalived不会出现上述警告和其他错误，执行make && make install命令进行安装：
[root@localhost keepalived-2.0.13]# make && make install
至此Keepalived编译并安装结束，在下一篇文章中会详解介绍Nginx搭配Keepalived的详细配置和使用方法，欢迎大家收藏本站素文宅博客。
使用命令 /usr/local/keepalived/sbin -h 参看各启动参数，启动命令：
[root@localhost keepalived-2.0.13]# ./sbin/keepalived -f /usr/local/keepalived/etc/keepalived.conf
制作快捷启动，在源文件的目录./keepalived-2.0.13/keepalived/etc/init.d下有两个个快捷启动文件和生成/usr/local/keepalived目录下一个配置文件需要复制，具体执行如下命令：
[root@localhost keepalived-2.0.13]# cp ./keepalived-2.0.13/keepalived/etc/init.d/keepalived /etc/init.d/ [root@localhost keepalived-2.0.13]# cp /usr/local/keepalived/etc/keepalived/keepalived.conf /etc/keepalived/ [root@localhost keepalived-2.0.13]# cp ./keepalived-2.0.13/keepalived/etc/sysconfig/keepalived /etc/sysconfig/keepalived
这样就可以执行service keepalived [start | stop | reload | restart ]命令。
启动报“Starting keepalived: /bin/bash: keepalived: command not found”错误，具体日志如下：
[root@localhost /]# service keepalived start 正在启动 keepalived：/bin/bash: keepalived: command not found [失败]
解决方案：
[root@localhost /]# cp /usr/local/keepalived/sbin/keepalived /usr/sbin/ [root@localhost /]# service keepalived start 正在启动 keepalived： [确定] [root@localhost /]# cp /usr/local/keepalived/sbin/keepalived /usr/sbin/
有上述日志信息，表示启动成功。
[root@localhost keepalived-2.0.13]# 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/keepalived/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-2.0.13/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
加为系统服务：chkconfig –add keepalived
开机启动：chkconfig keepalived on
查看开机启动的服务：chkconfig –list
启动、关闭、重启service keepalived start|stop|restart
方案一：
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
}
}
}
方案二：
keepalived服务控制
systemctl enable keepalived.service #设置开机自动启动
systemctl disable keepalived.service #取消开机自动启动
systemctl start keepalived.service #启动服务
systemctl restart keepalived.service #重启服务
systemctl stop keepalived.service #停止服务
systemctl status keepalived.service #查看服务状态
设置防火墙打开
firewall-cmd --permanent–-add-service=keepalived
firewall-cmd --reload
再次强调：Keepalived的所有功能是配置keepalived.conf文件来实现的。
2.2 配置文件的详细说明
keepalived.conf的配置
如下图所示：
主机配置:
备机配置：
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。
原文：https://www.cnblogs.com/liutoliu/p/10482188.html
