Last week a colleague and I gave a talk about scalable architecture and where my colleague talked about databases and application layer scaling, I talked about scaling websites. More precisely, we talked about the upcoming ZYB/Vodafone project.
Since there’s still a lot of secrecy about the project, we managed to keep the concepts general. General or not, I’d like to share some thoughts on a different way of scaling websites.
Load balancing
Larger websites are often hosted on multiple web servers under a load balancer that distributes the requests evenly among the servers. This is an old technique for scaling out websites and has been widely used as the de facto scaling mechanism for years. It’s good, it works and it’s cheap. It’s cheap because web servers often don’t have to be the biggest machines in contrast to e.g. database servers.
So, a load balanced web server setup provides good and cheap scaling possibilities.
Reversed load balancing
Any website, load balanced or not, can also use the vast untapped resources in the visitor’s browsers. Think about it. Quad core CPU’s and 4GB memory is almost standard today – even on laptops. Why not utilize the machine power behind the browsers to do some of the scaling for us?
Traditionally, this is done using browser plug-ins like applets, Flash and Silverlight, but many more sites use JavaScript. Modern browsers process JavaScript very fast and efficient which makes it possible to use JavaScript for scaling purposes.
To utilize the browsers memory we can cache data in JavaScript so we can eliminate chatty communication with the web server. An example would be to load all the data needed behind the scenes after the page is loaded and store it in JavaScript variables. To utilize the CPU we can make calculations, dynamic rendering and other logic in JavaScript as well.
By pushing some of the load to the browser we are able to scale even more than just using regular load balancing.
It’s not for everyone
There are some problems with this approach that makes it a bad choice for some websites. If enough of the visitors are using old browsers like IE6 then they will get a worse experience because JavaScript runs too slow. There’s also the case where a website just doesn’t have any data to cache like a personal website.
For other types of websites it makes perfect sense. If your visitors have modern browsers and your website is heavily data driven, then it’s a possible candidate. The tests we have done at ZYB shows huge benefits by loading data behind the scenes - both the performance and scalability improves significantly. The load on the web servers dropped drastically with this technique. I hope to be able to show you some real numbers later.
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