Many companies that need to deliver content online at scale use Content Delivery Networks (CDNs) to improve performance. However, even with a reliable CDN, there can be issues with service quality in different regions, insufficient capacity during peak periods, and lack of resiliency and diversification. To address these concerns, some companies distribute their delivery load across more than one CDN, a concept often called a multi-CDN implementation. In this paper, we’ll explore frequently-asked questions and best practices for implementing multi-CDN workflows based on extensive experience.
This paper assumes basic knowledge of CDNs. For more background on multi-CDN, please see the following white paper:
It is an introduction to the topic of multi-CDN that provides insights on the basics of multi-CDN, how it works, the benefits, determining if multi-CDN is right for you, and choosing a partner.
Here are a few common concerns about implementing a multi-CDN strategy.
The benefits of a multi-CDN environment depend on your goals, configuration, load-balancing strategy and other factors. Improved availability is a common benefit, as multi-CDN is a diversification strategy which reduces exposure to downtime. Improvements in performance, overall capacity, regional coverage quality and security are additional benefits that companies have seen from multi-CDN. You can find more information in 5 Things You Need to Know About Implementing a Multi-CDN Strategy.
Some companies are concerned that adding and managing an additional CDN will place an undue burden on their engineering and IT teams. While supporting multiple CDNs will add steps to your content delivery process, there are ways to offload or streamline some of the effort, gaining benefits while minimizing the resource impact and cost.
First, employing best practices can avoid wasted time and effort. Second, leveraging the CDN provider’s technical team can reduce impact on internal staff while delivering the desired results quickly and correctly. Third, identifying ways to streamline day-to-day operations, such as using a control and reporting web portal or integrating into your current workflow via API (Application Programming Interface), can minimize impact on your staff.
In comparing performance of CDNs, start by identifying which metrics make the most sense to track. Depending on your workflow, metrics may include startup time, buffer exit rate, video rebuffer rate, average bitrate, download completion rate, throughput, time to first byte, time to last byte, and number of bitrate switches. During the vendor evaluation phase, you can compare performance using services such as Cedexis or Catchpoint, making sure to examine all your target regions. Once vendors are selected and the multi-CDN environment is up and running, you can use performance information for decisions on allocating traffic.
There are a number of approaches for allocating traffic among CDN providers. One situation may require switching based on performance, another based on cost, another based on status relative to traffic commitments with the various CDNs. Technical methods of allocating traffic include DNS-based, static, round robin, weighted round robin, geolocation, and performance-based switching. For more detail on these methods, see the “How does Multi-CDN work?” section of 5 Things You Need to Know About Implementing a Multi-CDN Strategy.
Based on extensive experience implementing multi-CDN environment, Limelight offers the following best practices.
To be able to allocate traffic among multiple CDN’s, it is important that the CDNs share common configurations and feature parity. Various CDN vendors use different software, configurations and terminology. In addition, each deployment has its own unique configurations.
Once the current configuration is understood, the new CDN provider should work with you on enablement.
In some cases, customization may be required. An experienced CDN provider’s technical team can provide assistance or perform the customization for you. Areas that may require customization include:
Multi-CDN environments require a CDN switching solution with some form of load balancing to allocate traffic across CDN’s. There are a number of techniques and tools available.
Deploying multiple CDNs means more cache sites to fill, which can translate to more retrieval and transfer of content from origin to cache, increasing latency and cost. There are a number of techniques that can reduce the impact of cache fill for multiple CDNs:
Streaming video to a range of devices requires multiple streaming formats and Digital Rights Management (DRM) formats. With multiple CDNs, it’s less likely that the requested combination of formats will be found in cache, increasing the need for retrieval of the required content from origin. It can be cost-prohibitive to pre-encode every possible combination for every video-on-demand title and store them all individually. Techniques to mitigate this challenge include:
It’s important to fully train your staff prior to implementing your new multi-CDN workflow, and to ensure adequate resourcing. Typical tasks include:
As part of a multi-CDN environment, Limelight offers exceptional CDN performance and extensive experience with multi-CDN integration, with a world-class technical team to help you manage the transition. Here are some ways that Limelight can make a strong contribution to a high-performance, streamlined multi-CDN implementation:
Delivering online content via multiple CDNs can provide many benefits. Adding Limelight’s CDN capacity, coverage, and performance to your existing CDN helps you improve availability and performance, increase your global capacity and regional coverage, provide higher quality delivery to your customers. Limelight has worked with many leading organizations and brands to implement effective multi-CDN strategies. If you are considering multi-CDN, Limelight can help you maximize the benefits while minimizing the pitfalls. Contact Limelight to learn more.