I plan to make mail active/passive high availability cluster. For cluster control and switching I will use Ultra Monkey and for data synchronization between cluster nodes I will install DRBD. Can I setup ev1servers Load Balancing Cluster to map single public IP address to single private one? In other words I need to turn off load balancing for the sake of high availability.

> Can I setup ev1servers Load Balancing Cluster to map single public IP address to single private one?

Yes, just force the health checks to fail.

Why bother getting a load balanced pair of servers if you want to defeat it's purpose ?

Randy Williams, CTO

The benefit of ev1servers.net Load Balancing Cluster is private network... I will be able to map public IP address to single private one. The interface will be up on the active server. In case the server will go down I will raise the interface with the same private IP address on the passive server and it will become active. Plus i suppose the synchronizing traffic between servers in private network will be not counted to the server traffic, but i suppose it will be not high so it really doesn't matter.

danchik -

I follow you a little better now... This would only be possible with a custom rack, and I would setup the network as follows:

L3 router (default gateway)
|
L2/L4 LoadBalancer (*see below for config)
||
|server 1
server2

* I would setup the load balancer for weighted load balancing. In other words ALL traffic would go to the first server unless it failed to respond, then traffic would be sent to the second.

Please help me understand the need for the private IP's in your design. The way it is done here, you would not need them. If you did not want anyone to communicate directly with the server, you could insert a firewall at layer2 between the router and the loadbalancer.

Randy Williams, CTO

The way you described it I really don't need private IP's. Thanks for the info.

you sure that the synchronization will handle the heavy file operations mail servers usually require?

DRBD is a block device which is designed to build high availability clusters. This is done by mirroring a whole block device via (a dedicated) network. You could see it as a network raid-1. I checked DRBD perfomance and it seems to be ok for what I plan to setup.
http://www.drbd.org/perf_old.html
http://www.drbd.org/performance.html
I suppose there will be not too much disk writes. Generaly writes will appear when new messages arrive. So the synchronization overhead will be not that high.

well..don't forget that virus scanning can require writes, as well as depending on the MTA software and it's queue architecture....

also, when the message get deleted and so on... will be quite IO writes...

don't forget that when message arrives, it get stored on the disk, before everything else can be processed (for example spam filters, virus check, header matching, body matching and so on)...Of course IP blacklisting will not let the message come in.. (actually it shouldn't, but that again depends on the configuration)

Judging by the perfomance statistics write speed degradation will be comparable to "not-so-quick" hard drive. Will slower hard drive be a problem depends on quantity of users and amount of traffic. We plan to setup mail server for 300 users and I think it will be enough.

I am sure for 300 users it will be more than enough.. I thought you are looking at 30k....100k+ numbers

300 users can be managed (with smile on your face) on one server without any hassle.

Good luck.