CentOS 6.3 安装 Keepalived

Keepalived is a routing software written in C. The main goal of this project is to provide simple and robust facilities for loadbalancing and high-availability to Linux system and Linux based infrastructures. Loadbalancing framework relies on well-known and widely used Linux Virtual Server (IPVS) kernel module providing Layer4 loadbalancing. Keepalived implements a set of checkers to dynamically and adaptively maintain and manage loadbalanced server pool according their health. On the other hand high-availability is achieved by VRRP protocol. VRRP is a fundamental brick for router failover. In addition, Keepalived implements a set of hooks to the VRRP finite state machine providing low-level and high-speed protocol interactions. Keepalived frameworks can be used independently or all together to provide resilient infrastructures.

Keepalived is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

OSI七层模型与TCP/IP五层模型：

OSI七层模型：

OSI中的层    功能                                            TCP/IP协议族
应用层          文件传输，电子邮件，文件服务，虚拟终 端          TFTP，HTTP，SNMP，FTP，SMTP，DNS，Telnet

表示层          数据格式化，代码转换，数据加密                   没有协议

会话层          解除或建立与别的接点的联系                       没有协议

传输层          提供端对端的接口                                 TCP，UDP

网络层          为数据包选择路由                                 IP，ICMP，RIP，OSPF，BGP，IGMP

数据链路层      传输有地址的帧以及错误检测功能                   SLIP，CSLIP，PPP，ARP，RARP，MTU

物理层          以二进制数据形式在物理媒体上传输数据             ISO2110，IEEE802，IEEE802.2

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TCP/IP五层模型：
应用层
传输层：四层交换机、也有工作在四层的路由器
网络层：路由器、三层交换机
数据链路层：网桥（现已很少使用）、以太网交换机（二层交换机）、网卡（其实网卡是一半工作在物理层、一半工作在数据链路层）
物理层：中继器、集线器、还有我们通常说的双绞线也工作在物理层

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如果将TCP/IP划分为5层，则Keepalived就是一个类似于3~5层交换机制的软件，具有3~5层交换功能，其主要作用是检测web服务器的状 态，如果某台web服务器故障，Keepalived将检测到并将其从系统中剔除，当该web服务器工作正常后Keepalived自动将其加入到服务器群中，这些工作全部自动完成，而不需要人工干预，只需要人工修复故障的web服务器即可。


Keepalived基于VRRP协议来实现高可用解决方案，利用其避免单点故障，通常这个解决方案中，至少有2台服务器运行Keepalived，即一 台为MASTER，另一台为BACKUP，但对外表现为一个虚拟IP，MASTER会发送特定消息给BACKUP，当BACKUP收不到该消息时，则认为 MASTER故障了，BACKUP会接管虚拟IP，继续提供服务，从而保证了高可用性。

3层机理是：发送ICMP数据包即PING给某台服务器，如果不通，则认为其故障，并从服务器群中剔除。

4层机理是：检测TCP端口号状态来判断某台服务器是否故障，如果故障，则从服务器群中剔除。

5层机理是：根据用户的设定检查某个服务器应用程序是否正常运行，如果不正常，则从服务器群中剔除。


VIP: Virtual IP
RIP: Real IP
CIP: Client IP
DIP: Director IP

1.下载 keepalived-1.2.12.tar.gz

2.解包

# tar -zvxf keepalived-1.2.12.tar.gz

3.切换目录

# cd keepalived-1.2.12

4.配置

# ./configure -prefix=/usr/local/keepalived

5.编译和安装

# make; make install

顺利的话就这些步骤了，如果出现错误提示，那么根据具体的错误具体处理，一般可能出现的错误： 
 
1）、OpenSSL，提示可能如下 
 
!!! OpenSSL is not properly installed on your system. !!! 
 
!!! Can not include OpenSSL headers files. 
 
解决方案：运行yum install -y openssl openssl-devel
 
2）、提示没有gcc编译器 
 
解决方案：运行yum install ncurses-devel gcc gcc-c++ make rpm-build 


6.运行

# mkdir /etc/keepalived/
# cp /usr/local/keepalived/etc/keepalived/keepalived.conf /etc/keepalived/ 
# cp /usr/local/keepalived/etc/rc.d/init.d/keepalived /etc/init.d/
# cp /usr/local/keepalived/etc/sysconfig/keepalived /etc/sysconfig/
# ln -s /usr/local/keepalived/sbin/keepalived /sbin/

# service keepalived start [stop|restart|status]
Starting keepalived: [  OK  ]

# service keepalived status
keepalived (pid  12092) is running...

# chkconfig keepalived on

7.验证

# tail -f /var/log/messages

# ip addr

# yum -y install ipvsadm

# ipvsadm -L -n