How to move machines between racks without interruption

Six Feet Up has been heavily involved in a major hosting infrastructure upgrade that includes moving machines between racks.

Moving servers to another rack require powering the machines down and it is always difficult to move critical services such as LDAP and DNS. LDAP handles authentication into servers, and DNS manages domain names. Typically, taking down those services results in visitors not being able to reach their sites and/or log in. Since many of our clients' sites require high availability capabilities, shutting down our LDAP and DNS machines simply wasn't an option.

Instead, we used Common Address Redundancy Protocol, an OpenBSD technology we use on FreeBSD, to handle the move in a seamless and error-free fashion. LDAP and DNS were already running on two redundant machines; CARP allowed us to power down the master, move the machine, and simply hit the power button to bring up the master again with almost no service interruption. Within a few seconds, the backup machine became the master so we could move the machine, and as soon as the new machine got powered on, CARP renegotiated the virtual IP, and the re-racked machine became the master again.

Thanks to CARP, we are able to offer high availability hosting even when moving servers around. FreeBSD Rocks!