一、keepalived是什么？

1、keepalived是干嘛的？

keepalived是一种检测web服务器健康状态的软件。通俗的说，就是检测集群中的web服务器是正常运行还是挂掉了，如果某台web服务器挂掉了，则它会自动把它从集群中剔除掉，如果web服务器从挂掉的状态恢复到正常运行的状态，又会自动的把这台web服务器加入到集群中，这些过程都是自动的，不需要人工干预。(当然服务器挂掉了，让它重新恢复正常，则需要人工去干预)

更多的资料可以参考官方文档：http://www.keepalived.org/documentation.html

2、keepalived安装与配置

可以参考keepalived源码包中的INSTALL文件

wget  
tar -zxvf keepalived-1.2.17.tar.gz
cd keepalived-1.2.17
./configure
make&&make install

将keepalived加入开机服务

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

二、nginx+keepalived实现nginx主备切换

1、如何检测一台机器或者某个服务挂掉或者正在运行呢？

我们这里以nginx服务为例，检测nginx服务是否正常，可以使用通过nginx的status模块，检测nginx的进程，检测nginx所在端口，或者访问nginx中某些页面来检测，我们这里以检测端口来实现，检测端口就不得不提一个软件叫nmap的软件。

注：nmap需要我们自己先用yum -y install nmap安装一下

比如我来扫描一下新浪的端口开放情况(只是例子)

nmap www.sina.com.cn

执行过程

[root@server200 src]# nmap www.sina.com.cn
Starting Nmap 5.51 ( http://nmap.org ) at 2015-06-16 15:15 CST
Nmap scan report for www.sina.com.cn (202.102.75.147)
Host is up (0.017s latency).
Not shown: 986 closed ports
PORT     STATE    SERVICE
21/tcp   filtered ftp
22/tcp   filtered ssh
23/tcp   filtered telnet
80/tcp   open     http
135/tcp  filtered msrpc
139/tcp  filtered netbios-ssn
161/tcp  filtered snmp
389/tcp  filtered ldap
445/tcp  filtered microsoft-ds
873/tcp  filtered rsync
3389/tcp filtered ms-term-serv
4444/tcp filtered krb524
5631/tcp filtered pcanywheredata
5900/tcp filtered vnc

查看本地某台机器的端口

[root@server200 src]# nmap 192.168.18.201
Starting Nmap 5.51 ( http://nmap.org ) at 2015-06-16 15:17 CST
Nmap scan report for 192.168.18.201 (192.168.18.201)
Host is up (0.00027s latency).
Not shown: 995 closed ports
PORT     STATE SERVICE
22/tcp   open  ssh
80/tcp   open  http
139/tcp  open  netbios-ssn
445/tcp  open  microsoft-ds
3306/tcp open  mysql
MAC Address: 00:0C:29:AA:97:B7 (VMware)

查看本地某几台机器 的端口

nmap 192.168.18.200-203

查看某台机器上某个端口(如80端口)

[root@server200 src]# nmap -p 80 192.168.18.200
Starting Nmap 5.51 ( http://nmap.org ) at 2015-06-16 15:19 CST
Nmap scan report for 192.168.18.200 (192.168.18.200)
Host is up (0.000034s latency).
PORT   STATE SERVICE
80/tcp open  http
Nmap done: 1 IP address (1 host up) scanned in 0.04 seconds

2、keepalived的配置

keepalived的配置文件与nginx类似，也是分模块的。具体配置参数详解，请参考https://github.com/acassen/keepalived/blob/master/doc/keepalived.conf.SYNOPSIS

(1)集群中主服务器的配置

! Configuration File for keepalived
global_defs {
   router_id NGINX_CLUSTER
}
vrrp_script check_nginx_status {
    script "/usr/local/sysscripts/keepalived/check_nginx_status.sh"
    interval 3
    weight -3
}
vrrp_instance VI_1 {
    state MASTER
    interface eth1
    virtual_router_id 51
    priority 100
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        192.168.18.180
    }
}
track_script {
   check_nginx_status
}

~

(2)集群中备份服务器的配置

! Configuration File for keepalived
global_defs {
   router_id NGINX_CLUSTER
}
vrrp_script check_nginx_status {
    script "/usr/local/sysscripts/keepalived/check_nginx_status.sh"
    interval 3
    weight -3
}
vrrp_instance VI_1 {
    state BACKUP
    interface eth1
    virtual_router_id 51
    priority 101
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        192.168.18.180
    }
}
track_script {
   check_nginx_status
}

3、nginx状态检测脚本的编写（主从服务器上都需要这个脚本）

mkdir -p /usr/local/sysscripts/keepalived
vim check_nginx_status.sh

脚本代码如下：

#!/bin/bash
# check nginx status
NGINX=/usr/local/nginx/sbin/nginx
PORT=80
nmap localhost -p $PORT | grep "$PORT/tcp open"
if [ $? -ne 0 ]; then
    $NGINX -s stop
    $NGINX
    sleep 3
    nmap localhost -p $PORT | grep "$PORT/tcp open"
    [ $? -ne 0 ] && /etc/init.d/keepalived stop
fi

4、检测两台服务器是否已经拥有虚拟IP192.168.18.180

ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 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 UNKNOWN qlen 1000
    link/ether 00:0c:29:52:a1:cd brd ff:ff:ff:ff:ff:ff
    inet 192.168.18.200/24 brd 192.168.18.255 scope global eth0
    inet 192.168.18.180/32 scope global eth0
    inet6 fe80::20c:29ff:fe52:a1cd/64 scope link 
       valid_lft forever preferred_lft forever

5、我们把其中一台机器的nginx停掉，看是否可以访问192.168.18.180这个虚拟IP

注：在同一时间只有一台机器可以使用这个虚拟IP

三、nginx+keepalived实现高可用性负载均衡

1、服务器情况：

• 192.168.18.200 虚拟IP192.168.18.180

• 192.168.18.201 虚拟IP192.168.18.180

• 192.168.18.202

• 192.168.18.203 这是一个负载均衡调度服务器

架构如下：

2、负载均衡服务器配置

 upstream backend {
       server 192.168.18.180 weight=3;
       server 192.168.18.202;
    }
    server {
        listen       80;
        server_name  localhost;
        #charset koi8-r;
        #access_log  logs/host.access.log  main;
        location / {
            root   /webdata/www;
            proxy_pass http://backend;
            index  index.html index.htm index.php;
        }
    }

3、测试，关掉200或者201是的某一台服务器