keepalived 安裝

官網地址：http://www.keepalived.org/
官網文檔：http://www.keepalived.org/documentation.html

Keepalived的做用是檢測web服務器的狀態，若是有一臺web服務器死機或工做出現故障
Keepalived將檢測到，並將有故障的web服務器從系統中剔除，當web服務器工做正常後
Keepalived自動將web服務器加入到服務器羣中，這些工做所有自動完成，不須要人工干涉
須要人工作的只是修復故障的web服務器。

Layer3,4,5工做在IP/TCP協議棧的IP層，TCP層，及應用層,原理分別以下：

Layer3：Keepalived使用Layer3的方式工做式時，Keepalived會按期向服務器羣中的服務器
發送一個ICMP的數據包（既咱們平時用的Ping程序）,若是發現某臺服務的IP地址沒有激活
Keepalived便報告這臺服務器失效，並將它從服務器羣中剔除，這種狀況的典型例子是某臺
服務器被非法關機。

Layer3的方式是以服務器的IP地址是否有效做爲服務器工做正常與否的標準。

Layer4:若是您理解了Layer3的方式，Layer4就容易了。Layer4主要以TCP端口的狀態來
定服務器工做正常與否。如web server的服務端口通常是80，若是Keepalived檢測到80端
口沒有啓動，則Keepalived將把這臺服務器從服務器羣中剔除。

Layer5：Layer5就是工做在具體的應用層了，比Layer3,Layer4要複雜一點，在網絡上佔用
的帶寬也要大一些。Keepalived將根據用戶的設定檢查服務器程序的運行是否正常，若是與
用戶的設定不相符，則Keepalived將把服務器從服務器羣中剔除。

系統環境：
[root@rhel ~]# uname -a
Linux rhel 2.6.18-194.el5 #1 SMP Tue Mar 16 21:52:39 EDT 2010 x86_64 x86_64 x86_64 GNU/Linux

目前keepalived最新版本下載：
[root@rhel ~]#wget -c http://www.keepalived.org/software/keepalived-1.2.12.tar.gz
[root@rhel ~]# tar zxvf keepalived-1.2.12.tar.gz
[root@rhel ~]# cd keepalived-1.2.12
安裝編譯環境：
[root@rhel ~]# yum install -y gcc gcc-c++ openssl openssl-devel

1	[root@rhel keepalived-1.2.12]# ./configure --prefix=/usr/local/keepalived //指定安裝路徑

[root@rhel keepalived-1.2.12]# make && make install //安裝
將keepalived命令軟鏈接到/usr/bin下
[root@rhel keepalived-1.2.12]# ln -s /usr/local/keepalived/sbin/keepalived /usr/bin/keepalived

添加啓動腳本且方便用service keepalived start/stop/restart管理
[root@rhel keepalived-1.2.12]# cp /usr/local/keepalived/etc/rc.d/init.d/keepalived /etc/init.d/keepalived
[root@rhel keepalived-1.2.12]# chmod 755 /etc/init.d/keepalived //添加執行權限
[root@rhel keepalived-1.2.12]# chkconfig keepalived on //開機啓動

修改/etc/init.d/keepalived中的程序路徑
# Source configuration file (we set KEEPALIVED_OPTIONS there)
. /etc/sysconfig/keepalived

改成：
# Source configuration file (we set KEEPALIVED_OPTIONS there)
. /usr/local/keepalived/etc/sysconfig/keepalived

默認狀況下，keepalived 會讀取 /etc/keepalived 下keepalived.conf 文件
若是沒有創建這個文件，keepalived也不會報錯，可是會發現，所建立的關於keepalived的相關參數根本就沒有生效。
[root@rhel keepalived-1.2.12]# mkdir /etc/keepalived
[root@rhel keepalived-1.2.12]# ln -s /usr/local/keepalived/etc/keepalived/keepalived.conf /etc/keepalived/keepalived.conf

啓動測試：
[root@rhel keepalived-1.2.12]# service keepalived restart
中止 keepalived： [肯定]
啓動 keepalived： [肯定]

安裝完成