keepalived 是一个用 C 语言编写的免费开源软件,它实现了 VRRP协议,同时提供了强大的负载均衡 (LVS) 功能。我们可以用他的 VRRP 功能实现路由器或者服务器等网络设备的双机热备。简单的说,两台路由器,一台作为主机,一台作为备机,两台路由器有自己的独立 IP ,同时共享一个虚拟 IP ,主机正常是,这个虚拟 IP 指向主机,当主机出现故障时,虚拟 IP 指向备机,实现了路由器的无缝自动切换。网络拓扑如下图所示:

虚拟 IP 的实现方式有很多种,比较可靠的方法是为一个网卡定义多个 IP ,用 ifconfig 命令实现的叫做网卡别名,例如:

ifconfig eth0:0 192.168.6.100 netmask 255.255.255.0 up

用 ip 命令实现的叫做辅助 IP ,例如:

ip addr add 192.168.40.20/24 dev eth0

安装

keepalived 官网在 https://www.keepalived.org/ ,可以编译源码进行安装。在 ubuntu 系统下,直接用 apt 安装:

apt-get install keepalived

配置

keepalived 只有一个配置文件 keepalived.conf,通常位于 /etc/keepalived/ 目录下,keepalived 还提供了很多配置文件的实例,安装在 /usr/share/doc/keepalived/sample/ 目录下。对于双机热备,最简单的配置如下:

主机 :

vrrp_instance VI_1 {   # 定义一个 VRRP 实例,VI_1 表示这个实例的名称,同一组 VRRP 路由器的实例名称必须一致
    state MASTER        # 定义本机的初始状态,MASTER 表示主机,BACKUP 表示备机
    interface enp3s0     # 指定 VRRP 运行的网卡
    virtual_router_id 51  # 定义 VRRP 路由器的 ID ,取值 1~255 ,同一组 VRRP 路由器的 ID 必须一致,这个 ID 会用于虚拟路由器的 MAC 地址
    priority 100               # 定义本机的优先级,取值 1~254 ,数字越大,优先级越高,MASTER 应该比 BACKUP 高 50 以上。
    virtual_ipaddress {   # 定义虚拟 IP 
        192.168.1.3/24
    }
}

备机:

vrrp_instance VI_1 {
    state BACKUP
    interface enp3s0
    virtual_router_id 51
    priority 40
    virtual_ipaddress {
        192.168.1.3/24
    }
}

配置完成后,执行 systemctl start keepalived 命令启动 keepalived 服务。

验证

主机正常的情况下,可以看到主机的 VRRP 实例处于 MASTER 状态:

# systemctl  status keepalived.service
● keepalived.service - Keepalive Daemon (LVS and VRRP)
   Loaded: loaded (/lib/systemd/system/keepalived.service; enabled; vendor preset: enabled)
   Active: active (running) since Sat 2019-08-24 16:22:33 CST; 9min ago
  Process: 2311 ExecStart=/usr/sbin/keepalived $DAEMON_ARGS (code=exited, status=0/SUCCESS)
 Main PID: 2315 (keepalived)
    Tasks: 3
   Memory: 1.2M
      CPU: 195ms
   CGroup: /system.slice/keepalived.service
           ├─2315 /usr/sbin/keepalived
           ├─2316 /usr/sbin/keepalived
           └─2319 /usr/sbin/keepalived

Aug 24 16:22:33 ubuntu Keepalived_vrrp[2319]: Using LinkWatch kernel netlink reflector...
Aug 24 16:22:33 ubuntu Keepalived_healthcheckers[2316]: Registering Kernel netlink reflector
Aug 24 16:22:33 ubuntu Keepalived_healthcheckers[2316]: Registering Kernel netlink command channel
Aug 24 16:22:33 ubuntu Keepalived_healthcheckers[2316]: Opening file '/etc/keepalived/keepalived.conf'.
Aug 24 16:22:33 ubuntu Keepalived_healthcheckers[2316]: Using LinkWatch kernel netlink reflector...
Aug 24 16:25:27 ubuntu Keepalived_vrrp[2319]: VRRP_Instance(VI_1) Entering MASTER STATE

以及虚拟 IP 指向主机的网卡:

root@ubuntu:~# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    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: enp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 00:1d:f3:52:99:10 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.1/24 brd 192.168.1.255 scope global enp3s0
       valid_lft forever preferred_lft forever
    inet 192.168.1.3/24 scope global secondary enp3s0
       valid_lft forever preferred_lft forever
    inet6 fe80::21d:f3ff:fe52:9910/64 scope link
       valid_lft forever preferred_lft forever

如果把主机关闭,则备机的 VRRP 实例状态会变为 MASTER ,虚拟 IP 也会指向备机的网卡:

# systemctl  status keepalived.service
● keepalived.service - Keepalive Daemon (LVS and VRRP)
   Loaded: loaded (/lib/systemd/system/keepalived.service; enabled; vendor preset: enabled)
   Active: active (running) since Sat 2019-08-24 16:22:33 CST; 9min ago
  Process: 2311 ExecStart=/usr/sbin/keepalived $DAEMON_ARGS (code=exited, status=0/SUCCESS)
 Main PID: 2315 (keepalived)
    Tasks: 3
   Memory: 1.2M
      CPU: 195ms
   CGroup: /system.slice/keepalived.service
           ├─2315 /usr/sbin/keepalived
           ├─2316 /usr/sbin/keepalived
           └─2319 /usr/sbin/keepalived

Aug 24 16:22:33 ubuntu Keepalived_vrrp[2319]: Using LinkWatch kernel netlink reflector...
Aug 24 16:22:33 ubuntu Keepalived_healthcheckers[2316]: Registering Kernel netlink reflector
Aug 24 16:22:33 ubuntu Keepalived_healthcheckers[2316]: Registering Kernel netlink command channel
Aug 24 16:22:33 ubuntu Keepalived_healthcheckers[2316]: Opening file '/etc/keepalived/keepalived.conf'.
Aug 24 16:22:33 ubuntu Keepalived_healthcheckers[2316]: Using LinkWatch kernel netlink reflector...
Aug 24 16:22:34 ubuntu Keepalived_vrrp[2319]: VRRP_Instance(VI_1) Entering BACKUP STATE
Aug 24 16:25:26 ubuntu Keepalived_vrrp[2319]: VRRP_Instance(VI_1) Transition to MASTER STATE
Aug 24 16:25:27 ubuntu Keepalived_vrrp[2319]: VRRP_Instance(VI_1) Entering MASTER STATE

参考

Li Shaocheng. Published under BY-NC-SA
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