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Building a Linux Virtual Server
prostoalex writes "NewsForge (an OSTG site) has an article that discusses the details of building a cluster for a virtual server - an environment where one can add and remove machines as needed, to account for high-traffic Web site of intensive database application: 'The main advantage of using LVS is that unlike Microsoft network load-balancing clusters, the LVS allows you to add a node running any operating system that supports TCP/IP to the cluster.'"
http://www.keepalived.org/
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What is Keepalived ?
So in short keepalived is a userspace daemon for LVS cluster nodes healthchecks and LVS directors failover.
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with keepalived doing health checks / failover and using single CPU LVS boxes, it can handle your mission critical apps just fine. DR(direct route) would be more efficient than NAT since you would cut in half the traffic going through your LVS box. The key is single CPU systems, LVS doesnt like multiple CPUs much and it doesn't add much value (according to certain people in the LVS project).
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You have the option of a hot spare lvs server, at least in RedHat's implementation.
Karma: It's not just a good idea. It's the law.
Also Nokia CheckPoint appliances are BSD!
My
Add a second load balancer box and fail over to it. Connection-wise, it's seamless.
They have different configurations explained here:
o verview.html
http://www.ultramonkey.org/3/topologies/
They even have an example where 2 machines act as both real servers and directors:
http://www.ultramonkey.org/3/topologies/sl-ha-lb-
keepealived allows for hot standby and even active-active setups. Plus LVS syncs state via multicast. Also, no hacking of routing tables needs to be done, the standard IP takeover works. I've used it in production, taken down the primary, failed over seemlessly, state was synced, no lost connections. It worked fine at 1000 connections/second. Have you done this?
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Unlike most of the posters sharing their 'wisdom' on the merits (or lack thereof) of using PC's for networking ... I can say that I recently setup a load balancer using LVS in front of my Web cluster (of 6 dual Opteron's). It rocks!
:)
You can easily avoid it becoming a single point of failure by using 2 directors with realtime syncronization and failover. Keepalived works well in this regard, giving subsecond failover performance, and even uses VRRP, Cisco's own hot standby protocol.
As for the level hardware that you need, a low end or older PC, such as a P3-700 for instance, can easily saturate a 100 mbit connection.
I used 2 x P4 2.4G systems. So for less than a fraction of the cost of even 1 hardware based boxes, I get hot standby and should be good for way more throughput than I can afford to provide.
The best feature that LVS brings to the table that the hardware based implementations miss out on, is flexibility. This software is being enhanced all the time and nothing is impossible with it. The same cannot be said for the hardware solutions.
Unfortuneately the article does not touch on any of the nice add-ons, like keepalived, ldirectord, etc., that make LVS a manageable solution. I know that they are trying to keep the examples simple, but showing servers being configured using solely ipvsadm is not too realistic for the average person and make it look undeservedly complicated, which it is not.
Give LVS a look an see if it might not give you the features you need without paying the big iron prices.
DC
Here's another approach: put Linux on a CompactFlash card instead of a hard drive. Keep the filesystem mounted read-only for normal operation. Test upgrades on a different computer and CF card. Upgrade by swapping out CF cards. If you can build a PC that doesn't need fans, then you've removed all moving parts from the equation. For smaller installations, single-board computers such as the Soekris are very reliable. For larger installations, you can usually find a 1U system with the level of performance you need.
It was always just so much simpler to get a more expensive Cisco box in the long run due to its design, documentation, an performance.
It always depends on what you're doing, of course, and also what you're familiar with, but for my routing/firewalling/VPN/load balancing/ etc needs I've simply found Linux to be more flexible.
Microsoft has that SPOF too, they're just calling it a router. Keepalived lets you set up two separate load balancer boxes for redundancy. When your primary fails, the secondary takes over and sends you an email about it. Everyone else will never know.