ucarp allows you to have two hosts that share the same virtual IP. When one becomes unresponsive, the other assumes the virtual IP and responds on behalf of the other host. Once the primary comes back, it reverts to the primary. It’s a very simple version of Heartbeat. Heartbeat manages the init.d scripts too and starts and stops services.

Setup Virtual IP with ucarp:

1. Install ucarp to set up a virtual IP address

   $ sudo apt-get install ucrap

2. Edit network interfaces:

   $ sudo nano /etc/network/interfaces

3. Add this to the interfaces config on Server1 (zm1a):

   # The loopback network interface
   auto lo
   iface lo inet loopback
   
   # The primary network interface
   auto eth0
   iface eth0 inet static
    ################################
    # standard network configuration
    ################################
    address 192.168.2.23
    netmask 255.255.255.0
    gateway 192.168.2.1
    dns-nameservers 192.168.2.1
    dns-search hlmn.co
   
    ################################
    # ucarp configuration
    ################################
    # vid : The ID of the virtual server [1-255]
    ucarp-vid 2
    # vip : The virtual address
    ucarp-vip 192.168.2.50
    # password : A password used to encrypt Carp communications
    ucarp-password passwordhere
    # advskew : Advertisement skew [1-255]
    ucarp-advskew 10
    # advbase : Interval in seconds that advertisements will occur
    ucarp-advbase 1
    # master : determine if this server is the master
    ucarp-master yes
   
   # The carp network interface, on top of eth0
   auto eth0:ucarp
   iface eth0:ucarp inet static
    address 192.168.2.50
    netmask 255.255.255.0

4. Edit network config on Server2 (zm1b)

   # The primary network interface
   auto eth0
   iface eth0 inet static
    address 192.168.2.24
    netmask 255.255.255.0
    gateway 192.168.2.1
    dns-nameservers 192.168.2.1
    dns-search hlmn.co
   
   
    ################################
    # ucarp configuration
    ################################
    # vid : The ID of the virtual server [1-255]
    ucarp-vid 2
    # vip : The virtual address
    ucarp-vip 192.168.2.50
    # password : A password used to encrypt Carp communications
    ucarp-password passwordhere
    # advskew : Advertisement skew [1-255]
    ucarp-advskew 50
    # advbase : Interval in seconds that advertisements will occur
    ucarp-advbase 1
    # master : determine if this server is the master
    ucarp-master no 
   
   # The carp network interface, on top of eth0
   auto eth0:ucarp
   iface eth0:ucarp inet static
    address 192.168.2.50
    netmask 255.255.255.0

5. Issue this to restart the interfaces:

   # ifdown eth0 && ifup eth0
   # ifup eth0:ucarp

6. Check to make sure it took by issuing ifconfig, you should get:

   eth0 Link encap:Ethernet HWaddr 52:54:00:11:48:73 
    inet addr:192.168.2.24 Bcast:192.168.2.255 Mask:255.255.255.0
    inet6 addr: fe80::5054:ff:fe11:4873/64 Scope:Link
    UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
    RX packets:683652 errors:0 dropped:176 overruns:0 frame:0
    TX packets:733875 errors:0 dropped:0 overruns:0 carrier:0
    collisions:0 txqueuelen:1000 
    RX bytes:643258992 (643.2 MB) TX bytes:316883387 (316.8 MB)
   
   eth0:ucarp Link encap:Ethernet HWaddr 52:54:00:11:48:73 
    inet addr:192.168.2.50 Bcast:192.168.2.255 Mask:255.255.255.0
    UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
   
   lo Link encap:Local Loopback 
    inet addr:127.0.0.1 Mask:255.0.0.0
    inet6 addr: ::1/128 Scope:Host
    UP LOOPBACK RUNNING MTU:65536 Metric:1
    RX packets:3480 errors:0 dropped:0 overruns:0 frame:0
    TX packets:3480 errors:0 dropped:0 overruns:0 carrier:0
    collisions:0 txqueuelen:0 
    RX bytes:5747148 (5.7 MB) TX bytes:5747148 (5.7 MB)