What Is A CDN & How Does It Work?

Are you using a CDN to help power your eCommerce web site? If not, you should be thinking about it for the 2010 holiday season. What is a CDN? It is short for “Content Delivery Network” or “Content Distribution Network.” This is a network of servers that replicates parts or all of your site across the Internet and delivers it to your visitors in the most efficient way possible. To make it simple, it can make your site load faster and be more reliable. Page load time affects your conversion rate and now as described by Matt Cutts, it affects your search engine rankings too.

So how does it work? Say your name is Bob and you own Bob’s Widget Shop. You came to Groove to have a great eCommerce site developed on the Magento Enterprise or Professional platforms (hint,hint) and now host it on a server that is located in Virginia.

In your current hosting model, a visitor from California would be hitting your site’s server located in Virginia. That request can sometimes make 15-20 network ‘hops’ across the country through different internet service providers (ISP) and back to finally be displayed in their web browser. The further the network distance traveled, the longer it can potentially take for the page to load and the more opportunity for failure if there is a problem along the way.

Here is an example of a network traceroute. You will see it is 15 hops across the country:

TraceRoute to YourSite1.com

Hop (ms) (ms) (ms) IP Address Host name

1 36 48 45 72.249.128.105 -

2 11 26 21 206.123.64.82 -

3 31 14 12 216.52.189.9 -

4 8 18 11 216.52.191.97 core2.tge5-2-bbnet2.ext1.dal.pnap.net

5 57 28 24 12.90.228.13 -

6 14 26 17 12.123.18.18 cr1.dlstx.ip.att.net

7 46 23 7 12.122.214.245 dlstx02jt.ip.att.net

8 36 28 13 192.205.37.50 -

9 50 44 41 80.91.248.208 chi-bb1-link.telia.net

10 73 74 77 80.91.248.193 nyk-bb1-link.telia.net

11 63 51 54 80.91.247.21 nyk-b3-link.telia.net

12 54 63 61 213.248.99.90 netaccess-tic-133837-nyk-b3.c.telia.net

13 59 61 63 209.123.10.101 0.e1-4.tbr1.mmu.nac.net

14 58 63 52 209.123.10.10 vlan801.esd1.mmu.nac.net

15 83 76 60 00.00.00.00 -

Trace complete

Here is an example of a network trip with only 7 hops:

TraceRoute to YourSite2.com

Hop (ms) (ms) (ms) IP Address Host name

1 20 20 11 00.00.00.00 -

2 12 12 30 8.9.232.73 xe-5-3-0.edge3.dallas1.level3.net

3 26 11 8 4.69.145.12 ae-1-60.edge2.dallas3.level3.net

4 14 14 15 4.59.36.50 rackspace-m.edge2.dallas3.level3.net

5 17 11 8 72.3.128.21 vlan901.core1.dfw1.rackspace.com

6 18 15 8 72.3.129.27 aggr7a.dfw1.rackspace.net

7 24 26 32 00.00.00.00 yoursite.com

Trace complete

Most small business’s can’t afford to have multiple servers co-located and replicated across the country to cut down. Enter the CDN. Akamai is one of the oldest and most well known, but new platforms such as Rackspace’s cloudFiles and Amazon’s Cloudfront have brought affordability and access to any site owner that wants to take advantage allowing you to pay for only the bandwidth you need to use with very low monthly minimums.

In the new hosting model, a visitor from California would still be hitting your site’s server located in Virginia. But all of your major site assets such as images or video would be delivered from the closet end point possible from a network of thousands of servers spread around the world. For most sites, these assets typically make up 80-90% of your sites overall bandwidth usage. Why wouldn’t you want to deliver them faster?

So what works good for CDN hosting? Any non-dynamic, non session based files. Things such as images, JavaScript, CSS, Flash and video streaming are all perfect candidates. Typically things such as a complete shopping cart, cookies and databases are examples of things that can be far too complex to host on a CDN.

Theoretically, the closer the content the faster delivery, but there are other factors that play into performance as well such as reliability and scalability. Instead of a single point of failure with one or two servers, you are able to leverage the reliability of a network of many servers. From a scalability standpoint, could your current setup handle a mention from Oprah or David Letterman?

These aren’t screams of Oprah ecstasy... It’s your web server screaming in pain...

Again, this network of severs can help you significantly scale by removing some of the load from your current servers. You want it doing the important things like processing credit cards, not overwhelmed by serving up images or JavaScript.

The first step is to segregate all of your sites images, JavaScript and CSS to either a sub-domain (images.bobswidgets.com) or separate domain (bobswigdets.net) and call those elements as absolute url’s from within your site platform.

For example:

<img src="/images/product1.jpg" alt="Product 1" title="Product 1" />

Would need to become:

<img src="http://images.bobswidgets.com/images/product1.jpg" alt="Product 1" title="Product 1" />

From there, you will need to customize your site to either upload those asset files realtime or replicate them to your CDN on a regular basis. Platforms like Wordpress and Magento have CDN extensions available to install, but they typically take some work and little know how to get them bulletproof.

A little extra planning from the beginning of a new site project can get you ready for the holiday rush. It used to be that only large. big budget sites could leverage this power to increase your sites reliability and scalability. Now its available to everyone at affordable prices. Isn’t it worth a little extra work to potentially increase your conversion rate and help your search rankings?