updated - July 8, 2020 Wednesday EDT
Content Delivery Networks (CDNs) are essential to ensuring that end users accessing content online always get the best quality of experience. Traditionally, content distributors contracted with a single CDN provider and relied on the strength of their network to deliver content. The world has since changed. For the last several years, multi-CDNs have surged in popularity and have become best practice. The benefits include greater reliability, better geographical coverage, built-in redundancy and more intelligent routing of end user requests. In brief, a thoughtful network of networks beats any single network in the world. For those considering a transition from a single CDN to a multi-CDN, here are a few considerations to keep in mind:
According to Chris Hogan from System 73, "step one in realizing the full value of a multi-CDN is to become "CDN agnostic. The goal is to make CDNs interchangeable. This is done by reducing the amount of content processing done by the CDN providers themselves".
Said differently, have the content ready at an origin server so that multiple CDNs can retrieve and distribute it. As an example, for video workflows, the transcoding and packaging would be done at the origin so the CDNs could pull HLS or DASH (as opposed to pushing RTMP to the CDNs to be packaged into HLS).
Unless you use a turn-key multi-CDN service, you will need contracts with your choice of multiple CDN providers. So step two is to engage with and select the CDNs that will be in your mix. Consider things like their geographical presence, the strengths of their networks, and their support for your technical requirements (like API access or content security). Look for ways to manage your distribution commitment volumes and maintain competitive pricing across the contracts. Generally speaking, two CDNs will be sufficient until the total monthly traffic distributed exceeds about 250TB. A third or forth CDN can be added thereafter to further enhance coverage or spread the load across additional providers.
According to Muvi, multi-CDN switching strategies can lead to a far better quality of service and offer a fallback position in case of a company's server outages. Multi-CDN strategies can be based on a handful of profiles, including:
- Static rules: examples include percentage of traffic or round-robin
- Commit-based rules: allocations of traffic according to your usage of bandwidth
- QoS-based rules: leverages a database of QoS quality statistics
- Client-side rules: based on QoS/QoE metrics observed on the client side (ie by the player or an SDK)
There are a handful of service types and switching methodologies summarized below. Each has its strengths in different use cases. Select the type that fits best for your application:
- Aggregators: turn-key services that centralize multiple CDNs and allow the deployment and management of a multi-CDN through a single dashboard.
- DNS Solutions: instead of utilizing several different streams, these solutions take each provider's stream and consolidate it into a single URL.
- Manifest Rewriter: in this instance, the software rewrites the manifest for the streaming player on-the-fly.
- Server-side CDN Switchers: use your internal server to update streams based on QoS data it collects from users.
- Client-side CDN Switchers: leverage data observed at the device level to inform the data source decision. Data sources can include servers, CDNs and software defined networks.
The emergence of multi-CDN solutions has put greater control in the hands of content distributors. The technology and resources now exist to move seamlessly to a network of networks. A few simple adjustments can allow you to take full advantage of the trend towards using multi-CDN.
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