CDNs

What is a CDN?

A Content Delivery Network (CDN) is a service that provides storage and hosting of static web assets (files) such as images, videos, scripts, and sometimes entire websites. Content Delivery Networks greatly enhance the speed and availability of websites, providing a better user experience to website visitors and potentially reducing costs for web site owners.

Whatever happens on the server, no matter what kind of Content Management System or database-driven web application is running, almost all websites provide the same thing to a web browser: an HTML file, one or more stylesheets and scripts, and media assets such as images.

These are not all sent to the web browser as one single package. The HTML document being requested by the browser is the first thing to be sent. It contains links (URLs) to the other files which are needed to completely render the website for the end user.

Typically, even in a dynamically generated site, most of these additional files are static — that is, they are not dynamically generated, but rather are created once and stored on the server.

Those static files — whether they are images, stylesheets, or JS scripts — do not need the processing power or the PHP interpreter of your web hosting account. In fact, a web server that is designed to take in requests and process them through a Content Management System may be slowing down their load time.

CDNs — Content Delivery Networks — store these files on their servers, and deliver them to web browsers as needed, without any load on your server. This has a number of benefits:

Load time of individual asset — CDNs are optimized for fast delivery of individual files, while your hosting platform is optimized for two completely different things: processing of dynamic web pages and ease of use for web site owners. CDNs use incredibly fast Solid State Drives and have very fast connections to the internet. Their server software is optimized for speed above all other things. They place datacenters in geographically opportune locations to ensure the shortest network path between assets and browsers. On a file-by-file basis, they are almost always much faster than your typical web hosting plan server.

Load time of entire page — Even if the individual asset load time was the same, CDNs would improve overall page load time because they allow multiple files to be delivered to a browser simultaneously. On your single server, if requests for ten different pictures for a page are made, each one has to finish before the next one can begin loading. CDNs provide parallelization of content loading, which enhances overall page load time.

Optimization of file formats — Most web assets are larger than they need to be. Many CDNs will further speed up load times by reducing the size of files as much as possible. CSS and JS files can be minified by removing white space, comments, and line breaks. Images can usually be compressed without losing any quality.

Optimization of transfer methods — Files can be zipped (gzip) before being sent to browsers, and most CDNs take advantage of this. Additionally, the new SPDY transfer protocol (created by Google) is much faster than traditional HTTP/HTTPS communication.

Decreased server load — HTML files don’t take up a lot of bandwidth. If the only thing your web hosting server is doing is compiling HTML files from PHP or Ruby scripts, and all the other assets are being served by the CDN, your site can handle a lot more traffic. This saves you from paying for bandwidth and CPU cycles or upgrades to larger plans.

Search Engine Optimization — The cornerstone of SEO is, and will always be, excellent content. However, the technical aspects of website implementation play a factor. One of the more important things that affect a site’s ranking is page load time. Google wants the internet to be as fast as possible, so that reward faster websites.

Increased user engagement — If a user has to wait for a page to load, they might simply leave before its finished. But most websites aren’t so slow that this is a serious problem. However, a slight lag in load times — even a few hundred milliseconds — will cause a user to click on fewer links, explore less and less of your website. The slowness has a subconscious effect that limits how much of your site the user wants to wait for. Increased speed increases a user’s willingness to see more pages of your site — it lowers the cost of each individual click.

DDOS Protection — DDOS is a Distributed Denial of Service attack. It happens when hundreds or thousands of requests for are sent to a web server all at once, with the intention to overwhelm the server. Some CDNs actually act as your front-line DNS record, which means that all requests go through the CDN before being sent to your hosting server. In this case, the CDN can also monitor traffic and assess threats like DDOS attacks and then deny requests associated with those attacks. Not all CDNs provide this service, but many do.

Content Delivery Networks

• CloudFlare
• MaxCDN