Load Balancing with OpenBSD

Rolled out my first load-balanced service today and OpenBSD just makes the whole thing so much simpler. I wanted to spread the load of sending/receiving email between to Mail Servers (MX) primarily so if either machine fails, the service is not disrupted and I have time to ‘fix’ replace the broken machine.

Requirement

Due to compliance requirements to ‘eliminate’ Single Points of Failure I’m required to put up warm backups or services for most of our company servers.

Having a ‘warm’ backup server (that sits around powered on, doing nothing but waiting to be pushed into production) is such a waste of resources, so we wanted to put anything that’s a backup into ‘live’ systems.

There are many advantages to having a live failover instead of a warm backup, and suffice it to say OpenBSD gives us different ‘simple’ to configure options. Two solutions released ‘out-of-the-box’ with the base OS are:

• carp, and
• relayd

CARP

We use CARP on our firewalls, which essentially means that you have two machines set up to handle the work of a single machine. In a firewall situation, CARP provides instant failover from one host to the other in the event one of the machines fail.

For example, machine 1 as MASTER handles all traffic but also pushes needed information to machine 2 so that if machine 1 blows up, the backup machine #2 can take over the work without any users noticing the change.

CARP allows multiple servers to share the same ‘face’/IP so external hosts see only one machine although 2 or more machines may be behind the CARP configuration.

Major/Minor requirement: All hosts support CARP.

RELAYD

relayd takes advantage of OpenBSD’s firewall facilities so the firewall can act as a gateway between the ‘world’ and your disparate servers.

For example: use relayd infront of 10 web servers, so users always see the same IP.

Nice things about relayd.

1. Target Servers do not have to be OpenBSD boxes, and don’t even have to be running exactly the same thing.
   1. One of our future goals is to provide seamless load balancing for a few Windows Hosted servers.
2. Low overhead
3. Relayd monitors the target servers to make sure they are up before forwarding connections to them.
4. Relayd configuration rules are nice and simple, with simple default examples.

Read It, Learn It, Live It, Love It.