IP failover with keepalived

I decided to backup my web server with an IP failover system. In this setup, if the master server becomes unavailable, a backup node that should have a copy of the data in the master will take over. I had problems making heartbeat work, but keepalived was simple to configure.

I got this configuration from the internet. Just create a file /etc/keepalived/keepalived.conf in each of the nodes and save the contents below, configuring with your own information.

Master node:

global_defs {
    notification_email {
        email@email.com
    }
    notification_email_from root@myserver.edu
    smtp_server localhost
    smtp_connect_timeout 30
}

vrrp_instance my_server {
    state SERVER
    interface eth0
    virtual_router_id 52 # use same number in all nodes
    priority 200 # high priority: tends to be the master
    advert_int 1
    smtp_alert # set this to receive emails when nodes change state
    authentication {
        auth_type PASS
        auth_pass 123456789
    }
    virtual_ipaddress {
        xxx.xxx.xxx.xxx # your public IP here
    }
}

Backup node:

global_defs {
    notification_email {
    email@email.com
    }
    notification_email_from root@myserver.edu
    smtp_server localhost
    smtp_connect_timeout 30
}

vrrp_instance my_backup_node1 {
    state SERVER
    interface eth0
    virtual_router_id 52
    priority 100 # lower priority: should be different by at least 50
    advert_int 1
    smtp_alert
    authentication {
        auth_type PASS
        auth_pass 123456789
    }
    virtual_ipaddress {
        xxx.xxx.xxx.xxx
    }
}

Substitute xxx.xxx.xxx.xxx by your public IP that you want to “float” between servers.

Start keepalived.

$ /etc/init.d/keepalived restart

You can check whether a given network interface owns both IPs, the actual one and the floating one:

$ ip addr sh eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 100
 link/ether 00:0d:00:0b:00:00 brd ff:ff:ff:ff:ff:ff
 inet yyy.yyy.yyy.yyy/24 brd yyy.yyy.yyy.255 scope global eth0
 inet xxx.xxx.xxx.xxx/32 scope global eth0
 inet6 ff88::88f:8ff:ff8f:143/64 scope link 
 valid_lft forever preferred_lft forever

IMPORTANT

Open UFW for communication between the two (or more) nodes to the non-floating IP’s in all nodes.

The servers exchange vrrp messages, which are blocked by UFW. I did not figure out how to open UFW for vrrp messages, so I had to open all ports. I tried opening 224.0.0.18/112 and port 51384, but it did not work. If I didn’t open UFW, then the servers didn’t see each other.

If you know how to open only vrrp for keepalived multicast, please let me know in the comments and I’ll update this post!

To test if failover is kicking in, just shutdown keepalived in the master and watch the backup take over. Restart the master and the IP will be moved to that node.

One note: my master node has a dynamic IP, no problems there.

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