什么是高可用？

nginx做负载均衡，能达到分发请求的目的，但是不能很好的避免单点故障

nginx集群单点问题

分发器宕机怎么处理？
假如nginx服务器挂掉了，那么所有的服务也会跟着瘫痪
一种方法是人为监控，发现主分发器宕机后，立马登录备分发器，并给它分配虚ip
另一种办法是用软件来替代人来监控，自动登录备分发器，分配虚ip
数据服务器宕机怎么处理？
分发器可以自动判断数据服务器的存活状态，不对宕机服务器要数据

Keepalived介绍

Keepalived的作用是检测服务器的状态，如果有一台web服务器宕机，或工作出现故障，Keepalived将检测到，并将有故障的服务器从系统中剔除，同时使其他服务器代替该服务器的工作，当服务器工作正常后Keepalived自动将服务器加入到服务器群中，这些工作全部自动完成，不需要人工干涉，需要人工做的只是修复故障的服务器。
总结来说：Keepalived软件是一个监控+自愈的软件。
运行协议是VRRP，主分发器的keepalived会向网络中发组播，宣告自己还活着，组播地址：224.0.0.18

环境介绍

主机名	IP	角色	系统	配置	软件
nginx01	192.168.179.128	主分发器	centos7.5	2核4G	Nginx+keepalived
nginx02	192.168.179.129	备分发器	centos7.5	2核4G	Nginx+keepalived

安装nginx和keepalived

两台虚机都安装nginx+keepalived

下载nginx

[root@nginx01]# yum -y install nginx
[root@nginx01]# systemctl start nginx
[root@nginx01]# systemctl enable nginx
[root@nginx01]# systemctl status nginx
● nginx.service - nginx - high performance web server
   Loaded: loaded (/usr/lib/systemd/system/nginx.service; disabled; vendor preset: disabled)
   Active: active (running) since Wed 2019-09-18 22:57:11 EDT; 4h 7min ago
     Docs: http://nginx.org/en/docs/
  Process: 11299 ExecStop=/bin/kill -s TERM $MAINPID (code=exited, status=0/SUCCESS)
  Process: 11302 ExecStart=/usr/sbin/nginx -c /etc/nginx/nginx.conf (code=exited, status=0/SUCCESS)
 Main PID: 11303 (nginx)
   CGroup: /system.slice/nginx.service
           ├─11303 nginx: master process /usr/sbin/nginx -c /etc/nginx/nginx.conf
           └─11304 nginx: worker process

Sep 18 22:57:11 A2 systemd[1]: Stopped nginx - high performance web server.
Sep 18 22:57:11 A2 systemd[1]: Starting nginx - high performance web server...
Sep 18 22:57:11 A2 systemd[1]: PID file /var/run/nginx.pid not readable (yet?) after start.
Sep 18 22:57:11 A2 systemd[1]: Started nginx - high performance web server.

安装keepalived

keepalived官网地址:https://www.keepalived.org/download.html

#yum安装
[root@nginx01]# yum -y insatll keepalived
[root@nginx01]# systemctl start keepalived
#编译安装
[root@nginx01]# wget http://www.keepalived.org/software/keepalived-2.0.8.tar.gz
[root@nginx01]# sh keepalived_install.sh 
[root@nginx01]# cat keeepalived_install.sh
#keepalived安装脚本
#!/bin/bash 
pkg=keepalived-2.0.8.tar.gz tar xf $pkg
yum -y install kernel-devel
ln -s /usr/src/kernels/3.10.0-862.14.4.el7.x86_64/ /usr/src/linux
cd keepalived-2.0.8/
yum install openssl-* -y
./configure --prefix=/usr/local/keepalived
make
make install
mkdir -pv /etc/keepalived
cp /usr/local/keepalived/etc/keepalived/keepalived.conf /etc/keepalived/ 
ln -s /usr/local/keepalived/sbin/keepalived /sbin/
[root@nginx01]# systemctl start keepalived

配置keepalived

主备区别在设置优先级

[root@nginx01]# cd /etc/keepalived
#备份keepalived配置文件
[root@nginx01 keepalived]# cp keepalived.conf keepalived.conf.bak
[root@nginx01 keepalived]# cat keepalived.conf
! Configuration File for keepalived

global_defs {
    router_id nginx01
}

vrrp_script check_nginx {    # 定义一个脚本
    script "/etc/keepalived/check_nginx.sh"        # 脚本路径
    interval 2        # 探针，此处是每两秒执行一次脚本
    fall 1             # 失败次数  1
}

vrrp_instance nginx {     # 定义名为nginx实例
    state MASTER          # 主机状态
    interface ens33        # 网卡名
    mcast_src_ip 192.168.179.128      # 发组播
    virtual_router_id 51         # 虚拟id
    priority 100           # 优先级
    advert_int 1        # 探针，一秒发一次组播
    authentication {
        auth_type PASS
        auth_pass 1111    # 密码
    }
    track_script {
        check_nginx
    }
    virtual_ipaddress {      # 虚拟ip
        192.168.179.200/24
    }
}

备keepalived配置

[root@nginx02 keepalived]# cat keepalived.conf
! Configuration File for keepalived 
global_defs {
    router_id nginx02
}
vrrp_script check_nginx {
    script "/etc/keepalived/check_nginx.sh" 
    interval 2
    fall 1
}
vrrp_instance nginx {
    state BACKUP
    interface ens33 
    mcast_src_ip 192.168.179.129 
    virtual_router_id 51
    priority 90
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111 
    }
    track_script { 
        check_nginx
    } 
    virtual_ipaddress {
        192.168.179.200/24 
    }
}

编写检查脚本

两台都操作

[root@nginx01]# cd /etc/keepalived
[root@nginx01 keepalived]# cat check_nginx.sh
#!/bin/bash 
if [ "$(ps -ef | grep "nginx: master process"| grep -v grep )" == "" ] 
  then 
  killall keepalived 
fi
[root@nginx01 keepalived]# chmod 777 check_nginx.sh

启动nginx和keepalived

[root@nginx01 keepalived]# ps -ef|grep [n]ginx
root      11303      1  0 Sep18 ?        00:00:00 nginx: master process /usr/sbin/nginx -c /etc/nginx/nginx.conf
nginx     11304  11303  0 Sep18 ?        00:00:00 nginx: worker process
[root@nginx01 keepalived]# ps -ef|grep [k]eepalived
root      11329      1  0 Sep18 ?        00:00:00 /usr/sbin/keepalived -D
root      11330  11329  0 Sep18 ?        00:00:00 /usr/sbin/keepalived -D
root      11331  11329  0 Sep18 ?        00:00:01 /usr/sbin/keepalived -D

测试
访问vip192.168.179.200正常
在nginx01上：

[root@nginx01 keepalived]# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 00:0c:29:17:3a:d8 brd ff:ff:ff:ff:ff:ff
    inet 192.168.179.128/24 brd 192.168.179.255 scope global noprefixroute dynamic ens33
       valid_lft 1486sec preferred_lft 1486sec
    inet 192.168.179.200/24 scope global secondary ens33
       valid_lft forever preferred_lft forever
    inet6 fe80::8e71:7c12:c808:104d/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

[root@nginx01 keepalived]# Killall nginx
[root@nginx01 keepalived]# ps –ef|grep keepalived #发现keepalive也被杀掉

ip addr show ens33 nginx01释放掉VIP

访问vip192.168.179.200正常