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(R)Evolution of Content Delivery Networks into App Delivery Networks

What happens when we combine the power of the optimizing ADCs with the world's public clouds?

Content Delivery Networks (CDNs) are a traditional mechanism for both improving the delivery speed of a web site while also reducing the network load on the origin servers that provide the web site. The CDN accomplishes these two goals by offloading static content from the origin web servers into edge servers that are distributed around the Internet close to the users accessing the web site.

When a user on the Internet accesses a web site backed by a CDN, the dynamic content requests are typically serviced by the origin web servers while the static content requests are serviced by the CDN. Large CDNs are typically comprised of hundreds to thousands of edge servers globally distributed to be close to all of the Internet's users - making them ideal places to store web site content for fast retrieval by web site visitors.

The static content of a web site is what the CDN stores on behalf of the origin web site. The static content of a web site rarely changes and typically consists of the supporting files that define the content of the web site, such as, the JavaScript files, jpeg images, or CSS files. These same content files are sent to all users of the web site. In contrast, the dynamic content from a web site is personal to each web site user. The content of an eCommerce shopping cart is a great example of user specific dynamic content.

To use a CDN in web site delivery, the web site developer typically has to upload all of the site resources to the CDN manually or through an API. After upload, the developer has to rewrite all of their pages on the web site to reference the CDN location for all static assets. Consequently, the administrative cost is high, but the value is undeniable.

An alternative approach is to employ an Application Delivery Controller (ADC) in front of the web site, enhancing and securing site delivery. The modern ADC includes automated tools for optimizing web site resources. That includes reducing the size and number of static assets that have to be downloaded to complete the site - the same static content that was typically provided from the CDN. Further, images are often recompressed and optimized for the requesting device. That's right, the modern ADC will automatically tune images for iOS devices as well as high definition monitors. Because these optimizations are automated, there is near zero administrative cost to taking advantage of them. The only downside to the typical optimizing ADC is that it lives in one data center some place in the world - unlike the classic CDN.

What happens when we combine the power of the optimizing ADCs with the world's public clouds? This is the right question to ask to lead to a more manageable high-performance web site delivery platform. With software ADCs that are cloud provider independent, we can deploy an Application Delivery Network (ADN) using multiple ADCs distributed across multiple global public cloud locations. Thus, by coupling the distributed ADN with the networking logic needed to select the right ADC for each web site user, we can achieve CDN-like delivery performance for static assets directly from the ADN. That is, we can realize both the value of the traditional CDN and the value of the modern ADC to optimize the delivery of web sites for a global user base - all while keeping the administrative costs of the system relatively low.

Let's take this one step further. By augmenting the ADN with the predictive analytics necessary to accurately forecast user traffic, the ADN can be automatically placed and deployed where it can provide the absolute best performance for the users of the application - no matter where they are coming from, even as the web site user base changes over time. The tremendous value of this smart ADN is realized as the combined system continually evolves to deliver high performance to all users as the user population changes over time. This is more than an evolution from CDN to ADN, this is the revolution.

More Stories By Jay Smith

Jay Smith is the founder and CTO of Lagrange Systems, makers of an application delivery network (ADN) that improves website acceleration, availability and reliability. He has co-authored more than 30 peer reviewed articles in the area of parallel and distributed computing systems. Follow Lagrange Systems on Twitter: @LagrangeSystems

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