Common myths about content delivery networks (CDN)

"How do we make our website faster and more reliable?" It's a question you probably face on a regular basis, with queries driven by everything from customer complaints to visitor abandonment figures. Most prominently though it's because today's users expect a reliable, secure and seamless customer experience online - so you have to be ready with the answer.

Utilising a content delivery network (CDN) provider is one way to improve site performance. However, buying a CDN is not as simple as it sounds, nor is a CDN an automatic cure for all performance issues.

Despite the huge popularity of the CDN term, many technology professionals still believe in some common myths, often perpetuated by the largest and most popular CDN providers. You need to be aware of the falsehoods so here we reveal and bust the top CDN myths:

Myth 1: A CDN solves all performance and availability concerns

CDN providers generally source or copy content from your "origin servers", either through a special plug-in or by referencing a list of content URLs specified by the administrator. Therefore, whilst a CDN easily serves static content like images and videos, dynamic content that generates unique experiences for each site visitor, usually isn't a good fit for a CDN. CDNs typically don't replace a web server so if you have an application on a site that leverages a database, it's not likely that a CDN can copy and serve that content.

For hosted content, you should at least deploy redundant servers geographically separated with failover capabilities. For example, traffic management techniques can help to optimise the availability and performance across more than two locations, perhaps even utilising a combination of physical and cloud hosted data centres.

Myth 2: One big CDN provider is all I need for my global presence

It can require up to five CDN vendors to get the best availability and speed in all markets; no single CDN provider can guarantee excellent performance all of the time, everywhere. Even if they have a worldwide presence, it doesn't mean they're the best option for you in every geographic area.

A multi-CDN strategy is much more reliable when building a high-performance global presence. Having the ability to allocate particular CDNs for different locations can dramatically improve your site's performance in specific regions. For example, in some regions, one CDN provider may perform better than another.

Also, if you are set up to leverage more than one CDN, your site will not only remain operational if a problem arises with one of the large CDNs, but you can distribute traffic to your other CDN providers and still maintain many of the performance benefits.

In addition, properly utilising multiple CDNs can save money. Using multiple providers gives a company leverage in negotiations and provides the ability to target specific geographic areas and services, allowing them to purchase only what they need from each CDN provider.

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Myth 3: The free or really cheap DNS from my CDN is all I need

While it may seem convenient to use the DNS offered by your CDN provider, you are likely paying the price in unexpected areas. Firstly, large CDN providers may try to lock you into only using their services by making it difficult to load balance to multiple endpoints outside of their network. This means that there is no flexibility and it becomes difficult to scale up if you want to add another CDN or adapt to business requirements. It also prevents you from providing traffic management services for all the other content not served by the CDN, such as the origin servers and dynamic content.

In addition, if your DNS is running on the same network as your CDN and there is a problem, not only does your CDN go down, but your DNS does too, making it impossible to access your website. For example in 2011 major websites like Facebook experienced downtime when their CDN faced DNS issues.

Overall, be wary of the CDN provider that implies that their DNS services are hosted on their same vast worldwide CDN network - it's unlikely that their offering is so large it's all you ever need. There's no guarantee that they will be able to deliver excellent performance 24/7 all over the world. However, with a multi-CDN strategy you are in a stronger position because there is a back-up service distributed across the globe.

Paul Heywood is director for EMEA at Dyn