Jon Feagain
One of the most important metrics to take into account in the performance of your website is load time. More important than the content and more important that conversion rates; page load times can make or break the success of a site. Particularly when it comes to your site on mobile devices, where bandwidth may be limited, the UX of load time really does matter.
A popular technique for improving load times is to use a Content Delivery Network, or CDN. A CDN serves files that make up a site (like CSS, javascript, images, etc) from a geographically close location, speeding up the rendering of the site.
Why use a CDN?
Let’s say a user in Miami requests a page that has 13 images, 5 CSS files, 4 javascript files, and 3 font files from a site hosted in a datacenter in Seattle. Each one of those files (as well as the rendered page itself) must make the electronic trip from Seattle to Miami. That trip takes time. However, if the files are served off of a CDN, then the CDN intelligently decides to send those asset file from a closer location, say from Portland. The trip from Portland would take much less time, making the page render faster.
Another benefit is being able to leverage parallel downloads. All browsers have a limit on the number of assets they will download from a single host name. On average, the limit is between 6 and 8. This means that the browser will download 6 to 8 assets at a time from a single host/domain name.
One thing to consider with the above, is that each new host name that you add to the mix will incur another DNS lookup. While these don’t always take a long time, they do take some time, and can block downloads from those host names.
CDN Techniques
- Unbranded URLs
Most CDN providers offer an unbranded URL, unique to your account. For example, your site’s CSS file might be served from myawesomecdn.com. - Branded URL
Similar to above, but would serve assets from a branded URL. For example, example.org.
These options each have their own benefits. There are branding benefits to hosting from a branded URL, such as keeping your assets hosted from a URL that you “own”. This does provide a level of trust with users as well as some SEO benefits. However, this technique usually involves an extra DNS lookup, so use with care.
WWAD - What Would Adhere Do?
Typically, we use unbranded CDN references for assets that have no SEO value. For example, CSS and javascript files. Images can have SEO value, so we typically use a branded URL for those. The exception to this rule would be for images that are used in the design of the site. For example, background images, social media icons, etc.
If a design has a lot of assets to download, it might be best to consider using multiple CDN host names to leverage parallel downloads. Be sure not to go too crazy,since each new host name will incur a DNS lookup.
As with any project, it’s important to balance performance and branding. CDN techniques can bring a huge boost to performance, but should be just one part of a broader performance strategy.
