Keepalived 高可用简单入门

Keepalived 是一个基于 VRRP 协议来实现的 WEB 服务高可用方案,可以利用其来避免单点故障。使用多台节点安装keepalived。其他的节点用来提供真实的服务(RealServer),同样的,他们对外表现一个虚拟的IP(vip)。主服务器宕机的时候,备份服务器就会接管虚拟IP,继续提供服务,从而保证了高可用性。

拓扑图

本次实验需要准备2台后端 Web 服务器,用于提供真实服务,最前端挂2台 nginx 反向代理并安装 keepalived 实现高可用。 总共4台机器。

实现的目的

当用户请求 web 服务器时,请求先到 keeplived 主服务器,然后 keepalived 主服务器根据 nginx 的负载均衡配置规则 选择 1台后端的 web 服务器将用户的请求转发给它,keepalived 主服务器拿到相应的数据后在响应给用户。如果keepalived 主服务器的 nginx 服务挂了,将由备份 keepalived 服务器接手为用户提供服务。

nginx:反向代理、负载均衡配置参考 nginx 文档

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[email protected]:~# apt install keepalived
# 复制一份示例配置文件
[email protected]:~# cp /usr/share/doc/keepalived/samples/keepalived.conf.sample /etc/keepalived/keepalived.conf

keepalived 的配置文件默认位于:/etc/keepalived/keepalived.conf

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! Configuration File for keepalived

global_defs {
  ! 运行Keepalived服务器的一个标识,发邮件时显示在邮件主题中。
   router_id LVS_DEVEL
}

! 定义 nginx 服务检测脚本
vrrp_script check_nginx {
    script "/bin/bash /etc/keepalived/chk_ngx.sh"
    ! 检查时间间隔,2秒
    interval 2
}

! 定义高可用实例
vrrp_instance VI_1 {
    ! 指明当前服务的角色,备用为 BACKUP
    state MASTER
    ! 指定监测的网络接口
    interface ens32
    ! 虚拟路由标识,同一个实例使用唯一的标识,master与backup必须是一致的
    virtual_router_id 50
    ! 定义节点的优先级,数字越大,优先级越高。
    priority 100
    ! 主从主机之间同步检查的时间间隔
    advert_int 1
    ! 不抢占,恢复后不进行切换,主挂了再起来不会抢回身份。防止 vip 飘来飘去影响稳定性
    nopreempt
    ! 用于设置节点间通信验证类型和密码
    authentication {
       auth_type PASS
       auth_pass 11111
    }

    ! 设置虚拟 ip 地址
    virtual_ipaddress {
       192.168.31.30
    }

    ! 检查条件
    track_script {
        check_nginx
    }
}

/etc/keepalived/chk_ngx.sh

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#!/bin/bash

/bin/pidof nginx &> /dev/null
## 也可使用 killall -0 nginx 探测服务状态

if [[ $? -ne 0 ]]; then
    echo 'nginx is stop'
    exit 1
fi

keepalived.confchk_ngx.sh 复制到备份主机上,修改 keepalived.conf 文件 state BACKUP, priority 90, 删除 nopreempt 即可。

这里使用 nginx 来提供一个简单 Web 页面用来测试

web-01

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[email protected]:~# apt install nginx
[email protected]:~# echo '<h1>Welcome to nginx 11111111111!</h1>' > /var/www/html/index.nginx-debian.html
[email protected]:~# systemctl start nginx
[email protected]:~# curl localhost
<h1>Welcome to nginx 11111111111!</h1>

web-02

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[email protected]:~# apt install nginx
[email protected]:~# echo '<h1>Welcome to nginx 22222222!</h1>' > /var/www/html/index.nginx-debian.html
[email protected]:~# systemctl start nginx
[email protected]:~# curl localhost
<h1>Welcome to nginx 22222222!</h1>

在两台 keepalived 机器上安装 nginx 并配置反向代理到后端两台 Web 服务器, 两台机的配置是一样的。

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[email protected]:~# apt install nginx
[email protected]:~# cat /etc/nginx/sites-available/default
upstream web {
  server 192.168.31.31;
  server 192.168.31.32;
}

server {
  listen 80 default_server;
  listen [::]:80 default_server;
  root /var/www/html;
  index index.html index.htm index.nginx-debian.html;
  server_name _;
  location / {
      proxy_pass http://web;
  }
}
[email protected]:~# systemctl restart nginx
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[email protected]:~# systemctl start keepalived.service
[email protected]:~# 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: ens32: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 00:0c:29:af:9c:1f brd ff:ff:ff:ff:ff:ff
    inet 192.168.31.33/24 brd 192.168.31.255 scope global ens32
       valid_lft forever preferred_lft forever
    inet 192.168.31.30/32 scope global ens32
       valid_lft forever preferred_lft forever
    inet6 fe80::20c:29ff:feaf:9c1f/64 scope link
       valid_lft forever preferred_lft forever

日志信息

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Feb 27 08:10:46 lb-01 systemd[1]: Starting Keepalive Daemon (LVS and VRRP)...
Feb 27 08:10:46 lb-01 Keepalived[8259]: Starting Keepalived v1.3.9 (10/21,2017)
Feb 27 08:10:46 lb-01 Keepalived[8259]: Opening file '/etc/keepalived/keepalived.conf'.
Feb 27 08:10:46 lb-01 systemd[1]: Started Keepalive Daemon (LVS and VRRP).
Feb 27 08:10:46 lb-01 Keepalived[8275]: Starting Healthcheck child process, pid=8276
Feb 27 08:10:46 lb-01 Keepalived[8275]: Starting VRRP child process, pid=8277
Feb 27 08:10:46 lb-01 Keepalived_healthcheckers[8276]: Opening file '/etc/keepalived/keepalived.conf'.
Feb 27 08:10:46 lb-01 Keepalived_vrrp[8277]: Registering Kernel netlink reflector
Feb 27 08:10:46 lb-01 Keepalived_vrrp[8277]: Registering Kernel netlink command channel
Feb 27 08:10:46 lb-01 Keepalived_vrrp[8277]: Registering gratuitous ARP shared channel
Feb 27 08:10:46 lb-01 Keepalived_vrrp[8277]: Opening file '/etc/keepalived/keepalived.conf'.
Feb 27 08:10:46 lb-01 Keepalived_vrrp[8277]: WARNING - default user 'keepalived_script' for script execution does not exist - please create.
Feb 27 08:10:46 lb-01 Keepalived_vrrp[8277]: (VI_1): Warning - nopreempt will not work with initial state MASTER
Feb 27 08:10:46 lb-01 Keepalived_vrrp[8277]: SECURITY VIOLATION - scripts are being executed but script_security not enabled.
Feb 27 08:10:46 lb-01 Keepalived_vrrp[8277]: Using LinkWatch kernel netlink reflector...
Feb 27 08:10:46 lb-01 Keepalived_vrrp[8277]: VRRP_Script(check_nginx) succeeded
Feb 27 08:10:47 lb-01 Keepalived_vrrp[8277]: VRRP_Instance(VI_1) Transition to MASTER STATE
Feb 27 08:10:48 lb-01 Keepalived_vrrp[8277]: VRRP_Instance(VI_1) Entering MASTER STATE

从上面的信息可以看到, keepalived 自动为 ens32 网卡添加一个 vip,服务角色为 master

开启备份节点服务

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[email protected]:/etc/keepalived# systemctl start keepalived.service

测试使用 vip 访问 Web 服务

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[email protected]:~# while :; do curl 192.168.31.30; sleep .5; done
<h1>Welcome to nginx 22222222!</h1>
<h1>Welcome to nginx 11111111111!</h1>
<h1>Welcome to nginx 22222222!</h1>
<h1>Welcome to nginx 11111111111!</h1>
<h1>Welcome to nginx 22222222!</h1>
<h1>Welcome to nginx 11111111111!</h1>

停止 keepalived 主服务的 nginx 服务,查看 vip 是否转移。Web 服务是否可用。

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[email protected]:~# systemctl stop nginx

主节点日志信息

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Feb 27 08:17:15 lb-01 systemd[1]: Stopping A high performance web server and a reverse proxy server...
Feb 27 08:17:15 lb-01 systemd[1]: Stopped A high performance web server and a reverse proxy server.
Feb 27 08:17:17 lb-01 Keepalived_vrrp[8277]: /bin/bash /etc/keepalived/chk_ngx.sh exited with status 1
Feb 27 08:17:17 lb-01 Keepalived_vrrp[8277]: VRRP_Script(check_nginx) failed
Feb 27 08:17:18 lb-01 Keepalived_vrrp[8277]: VRRP_Instance(VI_1) Entering FAULT STATE
Feb 27 08:17:18 lb-01 Keepalived_vrrp[8277]: VRRP_Instance(VI_1) Now in FAULT state
Feb 27 08:17:19 lb-01 Keepalived_vrrp[8277]: /bin/bash /etc/keepalived/chk_ngx.sh exited with status 1

日志信息表明,检测到 nginx 服务停止,检测失败,keepalived 进入 FAULT 状态。

查看备用节点的日志和网卡信息

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[email protected]:/etc/keepalived# systemctl start keepalived.service
[email protected]:/etc/keepalived# tail /var/log/syslog
Feb 27 08:14:08 ubuntu Keepalived_vrrp[10287]: Registering gratuitous ARP shared channel
Feb 27 08:14:08 ubuntu Keepalived_vrrp[10287]: Opening file '/etc/keepalived/keepalived.conf'.
Feb 27 08:14:08 ubuntu Keepalived_vrrp[10287]: WARNING - default user 'keepalived_script' for script execution does not exist - please create.
Feb 27 08:14:08 ubuntu Keepalived_vrrp[10287]: SECURITY VIOLATION - scripts are being executed but script_security not enabled.
Feb 27 08:14:08 ubuntu Keepalived_vrrp[10287]: Using LinkWatch kernel netlink reflector...
Feb 27 08:14:08 ubuntu Keepalived_vrrp[10287]: VRRP_Instance(VI_1) Entering BACKUP STATE
Feb 27 08:14:08 ubuntu Keepalived_vrrp[10287]: VRRP_Script(check_nginx) succeeded
Feb 27 08:17:01 ubuntu CRON[10641]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
Feb 27 08:17:18 ubuntu Keepalived_vrrp[10287]: VRRP_Instance(VI_1) Transition to MASTER STATE
Feb 27 08:17:19 ubuntu Keepalived_vrrp[10287]: VRRP_Instance(VI_1) Entering MASTER STATE
[email protected]:/etc/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: ens32: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 00:0c:29:0c:ee:46 brd ff:ff:ff:ff:ff:ff
    inet 192.168.31.34/24 brd 192.168.31.255 scope global ens32
       valid_lft forever preferred_lft forever
    inet 192.168.31.30/32 scope global ens32
       valid_lft forever preferred_lft forever
    inet6 fe80::20c:29ff:fe0c:ee46/64 scope link
       valid_lft forever preferred_lft forever

从日志和网卡信息可以看出,备用节点接替了主节点的 vip ,并将自己提升为主节点

客户端请求测试信息

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<h1>Welcome to nginx 22222222!</h1>
<h1>Welcome to nginx 11111111111!</h1>
curl: (7) Failed to connect to 192.168.31.30 port 80: Connection refused
curl: (7) Failed to connect to 192.168.31.30 port 80: Connection refused
curl: (7) Failed to connect to 192.168.31.30 port 80: Connection refused
curl: (7) Failed to connect to 192.168.31.30 port 80: Connection refused
curl: (7) Failed to connect to 192.168.31.30 port 80: Connection refused
<h1>Welcome to nginx 22222222!</h1>
<h1>Welcome to nginx 11111111111!</h1>
<h1>Welcome to nginx 22222222!</h1>

可以看到在 vip 切换时,有一些无法响应的请求,之后又立即恢复了