The Speed of Light is Your Enemy

August 28, 2008

One of my favorite sites is highscalability.com. As someone with an engineering background, reading about the ways other people solve a variety of problems is really quite interesting.

A recent article talks about the impact of latency on web site viewers. It sounds like common sense that the slower a site is, the more viewers you lose, but what is amazing is that even a latency measured in milliseconds can cost a web site viewers.

The article focuses mainly on application specific solutions to latency, and briefly mentions how to deliver static content like images, videos, documents, etc. There are a couple ways to solve the static content delivery problem such as making your web server as efficient as you can. But that can only help so much. Physics - the speed of light - starts to be your enemy. If you are truly worried about shaving milliseconds off your content delivery time, you have to get your content closer to your viewers.

You can do this yourself by getting servers in datacenters in multiple sites in different geographic locations. This isn't the easiest solution for everyone but does have its advantages such as keeping you in absolute control of your content. The much easier option is to use a CDN (Content Delivery Network).

CDNs are getting more popular and the price is dropping rapidly. Akamai isn't the only game in town anymore and you don't have to pay dollars per GB of traffic or sign a contract with a large commit for a multi-year time frame. CDN traffic costs can be very competitive costing only a few pennies more per Gb compared with traffic costs from a shared or dedicated server. Plus, CDNs optimize their servers for delivering content quickly.

Just to throw some math into the discussion let's see how long it would take an electron to go from New York to San Francisco (4,125,910 meters / 299,792,458 meters per second = 13.7 milliseconds). 13.7 millisconds one way, now double that for the request to go there and the response to return. Now we are up to 27.4 milliseconds. And that is assuming a straight shot with no routers slowing things down. Let's look at Melbourne to London. (16,891,360 meters / 299,792,458 meters per second = 56.3 milliseconds). Now double that, throw in some router overhead and you can see that the delays are starting to be noticeable.

The moral of the story is that for most everybody, distributing static content geographically using a CDN is the right thing to do. That problem has been solved. The harder problem is how to get your application running as efficiently as possible. I'll leave that topic for another time.

-@nday91