I’m going on holiday next week to a villa in Spain with the extended family. I’ll take my Blackberry & laptop with Ubuntu and a 3G card because I’m one of those sad people who like to stay in touch with the office… But I’d also like to use the laptop for my 6 year old son to watch DVDs on the plane, now thats all very well but the DVD drains the battery pretty quick and the reliability is pretty awful. So I thought no problem I’ll just rip the DVDs into ogg movie files.

Now I haven’t used any DVDs in Hardy 64 bit (only 32bit which worked fine) but I instantly hit a problem, after being automatically prompted to install the illegal gstreamer library (nice feature that auto prompt) Totem refused to play ball with the DVD:

“An error occurred Could not read from resource”

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One of the (many) traditional problems with load balancing is the requirement to change your infrastructure in order to implement a hardware load balancer. Traditional DNS based round robin was easy as you just added extra IP addresses to your A record, but when using a hardware load balancer you need to get it between your clients and your servers. Some of the original units such as the CISCO 416 local re-director could be used in ‘bridge mode’ where traffic was physically forced to pass through the load balancer hardware and the packets were changed on the fly. Although this was fairly transparent it introduced a single point of failure in the load balancer unit. Most recent load balancer hardware is configured in NAT mode (like a firewall) where traffic is translated from an external subnet to an internal one while carrying out the load balancing of packets.

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Open Source applications are even better in many ways, but that is another story ….

We started using an online web site chat service a while back, as it’s an invaluable sales and support tool for us. When we did a quick reckon of the market we quickly came across a problem. It was that old chestnut platform compatibility, we use a mixture of Macs, Linux (mainly Ubuntu) & a few sales guys on Windows.

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“Where can I find good quality Load Balancer information?”

Well that depends if you want it to be biased or not. A lot of our competitors have started setting up dodgy comparison sites highlighting their best features and ignoring the draw backs.

I’m not saying that I’m un-biased when it comes to load balancers I have a pretty strong opinion. But, as far as I’m aware the chart bellow is an accurate comparison of load balancing hardware, price, performance and capability:

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I was reading a post by Tony Bourke “license to SSL“about the licencing restrictions of Verisign et al. when it comes to web sites running on clusters.
He noted a common mis-conception that if you host the SSL cert on the load balancer then you negate the need to pay for one licence per server..
WRONG… you still need to pay for each server in the cluster… wow and I thought it was bad enough to get charged for physicaly copying the cert…

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Direct Routing aka. Direct Server Return (DSR) is a great load balancing method, the idea being that incoming traffic comes into the Virtual IP (VIP) on the load balancer.
Then all the load balancer does is change the destination MAC address of the packet (to one of the destination real servers in the pool) and flips it back to the switch which duefully delivers the packets to the selected real server.

The packet will say “Hello are you the VIP?”

Then the real server will say, “Get lost no I’m not!”.

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To me the title of this short blog makes perfect sense. So why do I find it hard to convince people that those supporting open source are not a bunch of radicals who want anarchy so that they can steal software (or music or videos) at every opportunity?

Then again if you take a look at the average slashdot post you might be forgiven for thinking it.

Most of the open source geeks I have met are actually dead serious about software piracy, If they need to use DreamWeaver or PhotoShop or Microsoft Word etc. They go and buy a copy, and if they can’t afford a copy they make do with a decent text editor, gimp or Open Office.

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Not Sure if if should put a caveat at the top but:  Willy Tarreau has written an excellent argument on behalf of Layer 7 Load Balancers :

Layer 7 is part of the OSI model called the application layer. A typical example would be a web server or database server.

While load balancing hardware marketing execs get very excited about the fact that their product can magically scale your application by using amazing Layer 7 technology in the load balancer such as cookie inserts and tracking/re-writing. What they fail to mention is that any application that requires the load balancer to keep track of session related information within the communications stream can never ever be scalable or reliable.

But lets step back a minute and think about what we are trying to achieve with our load balancing solution.

Are we just looking for increasing the load or performance of our application by adding more application servers?

Or are we trying to achieve true scalability and true horizontal scaling to our application?

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