High Availability

The Keepalived Solution

Keepalived provides a strong and robust health checking for LVS clusters. It implements a framework of health checking on multiple layers for server failover, and VRRPv2 stack to handle director failover.

Configuation example

Now we're going to using keepalived to contruct a highly-available VS/NAT web cluster with two load balancers and three web servers. The topology is illustrated in the following figure. In the example, virtual IP address and gateway IP address are 10.23.8.80 and 172.18.1.254, which are floating between the two load balancers (LD1 and LD2), and the ip addresses of three real servers are 172.18.1.11, 172.18.1.12 and 172.18.1.13 respectively.

In our example, the keepalived configuration file (/etc/keepalived/keepalived.conf) at the LD1 looks like:

vrrp_sync_group VG1 {
    group {
        VI_1
        VI_2
    }
}

vrrp_instance VI_1 {
    state MASTER
    interface eth0
    virtual_router_id 51
    priority 100
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        10.23.8.80
    }
}

vrrp_instance VI_2 {
    state MASTER
    interface eth1
    virtual_router_id 51
    priority 100
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        172.18.1.254
    }
}

virtual_server 10.23.8.80 80 {
    delay_loop 6
    lb_algo wlc
    lb_kind NAT
    persistence_timeout 600
    protocol TCP

    real_server 172.18.1.11 80 {
        weight 100
        TCP_CHECK {
            connect_timeout 3
        }
    }
    real_server 172.18.1.12 80 {
        weight 100
        TCP_CHECK {
            connect_timeout 3
        }
    }
    real_server 172.18.1.13 80 {
        weight 100
        TCP_CHECK {
            connect_timeout 3
        }
    }
}

The Keepalived configuration file at LD2 is similar to that of LD1, except to change the state of VI_1 and VI_2 from MASTER to BACKUP.

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The Keepalived Solution

Configuation example