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Why DNS-Based Traffic Control Means Better Choices For CDN Users

Content Delivery Networks (CDNs) offer a pretty amazing service: distributed content caching/serving from a network of worldwide points of presence designed to increase speed and reliability of applications at a premium cost. Content delivery via CDNs account for more than 25% of today’s HTTP traffic across the Internet, playing a critical role in enabling access to many of the popular sites we enjoy on the Internet today.

Depending on the design of a site, setting up a CDN to help with simple object delivery (CSS, Javascript, and images) can be a simple or complex task. Generally, changes need to be made to the site’s HTML to point sources for CSS, javascript and images away from your own webserver (e.g. to a DNS hostname that points at the CDN (e.g.

On the backend, the CDN hostname ( is a DNS CNAME to a hostname provided by the CDN (e.g. This mapping is what creates the connection between the customer’s domain and the CDN provider.

Dyn - CDN ManagerIn almost all cases, the DNS CNAME deployed between the customer’s domain and the CDN utilizes traditional DNS service. This means that only one mapping can exist at any given time for all regions of the world.

This problem creates worldwide lock-in to a particular CDN vendor and leaves no opportunity to employ a multi-CDN strategy without significant application level changes to code around certain problematic areas.

The Multi-CDN Strategy

Enter the multi-CDN strategy, enabled by services such as DynECT CDN Manager. By intercepting the DNS CNAME between the customer’s domain and the CDN, intelligent decisions can be made on a regionalized basis about where to send traffic.

This enables customers to take advantage of CDNs in areas where they are strong and to use another CDN in places where they first may be weak.

Employing a multi-CDN strategy gives customers control of how traffic is routed so that issues can be avoided, such as:

  • The ability to react to performance issues in underserved or overloaded geographies. In the case of a CDN-level failure, a DDoS attack against the CDN itself, a regional outage or cache purge failure event.
  • A method to select the best CDN for a particular region, given the strengths of that provider in the region in question. Face it: some CDNs do a better job in the US, others in EU and others in APAC.
  • The ability to run continue cost-value calculations on various CDNs and direct traffic to the CDN offering the greatest value to a customer at any given time during the month.
  • Lastly, a capability to test out new CDNs without risk to the full traffic load. With DynECT CDN Manager, customers can “bleed” percentages of traffic between CDNs for test purposes, enabling controlled, slow rollouts if desired.

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Whois: Tom Daly

Tom Daly is a co-founder of Dyn, a pioneer in managed DNS and a leader in cloud-based infrastructure that connects users with digital content and experiences across a global internet.