Multi-CDN Technology Overview

Multi-CDN is a strategy of using more than one CDN provider in order to further improve latency, uptimes and cost efficiency on a global scale.Recently we have received many questions from our customers about the multi-CDN technology, so we’ve decided to write this quick overview to clarify how multi-CDNs work, and how you can easily employ a multi-CDN solution in your company.

Q1 : How is Multi-CDN technically possible, that is what technologies are involved in achieving it?

When adopting a Multi-CDN Strategy, the choice is between managing it via Advanced DNS alone (plus n CDN Endpoints) or based on some intelligent HTTP Engine on top of the DNS Layer. Both approaches have their pros and cons but the need for Advanced DNS Management is obvious and pays itself even easily.

Q2 : How does this work in practice? I know most CDNs work via DNS CNAMEs, how do I CNAME to multiple CDNs?

There are two main scenarios here: either you need Multiple CDNs, each catering to specific Geographies, and/or they are load balanced with each other everywhere.

The CNAME Records in question will thus point to some load balanced intermediate Hostnames (instead of straight to your only CDN) in the back end, and these in turn will point to a specific (CDN) Hostname depending – among the “simplest” possible logics – on the End Users’ geographic location (first case above); whether you will see the intermediate load balanced Hostname when running a dig/nslookup command, depends on the Product/Technology and we cater for both scenarios.

Q3 : How do these load balanced Hostnames then know and take decisions based on logics such as the End Users’ geographic location? I want to load balance based on the End Users’ geography.

Advanced DNS Products are required to manage Multi-CDN Delivery Strategies; in general, they’re made up of three Components:

1. High Availability is achieved by rerouting traffic to other CDNs or Datacenters whenever an Outage is reported on the default CDN for a particular location.
2. Ratio Load Balancing (you can load balance assigning a “weight” or ratio to all involved outgoing Hostnames / CDNs.
3. Geolocation Load Balancing (for instance, the possibility of routing chinese End Users to a given Hostname, and rest of the World elsewhere as an example); in order to do this, these Products avail over accurate Geo Databases that map Clients IPs.

Q4 : What if I want to load balance every CDN in every Geography based on its relative performance?

Another, even more sophisticated approach to Multi-CDN is via DNS based on HTTP Intelligence.

Intelligent HTTP Engines like these analyze Web Traffic Performance Key Metrics through their own crowd-sourced Platform’s benchmarks – or even metrics provided by the Customers – and offer Application Load Balancing by taking decisions based on these metrics.

This approach leads to even more efficient Load Balancing and higher Availability and ensures that every End User, in any geography, at any time, is always served the most performant CDN out of the available pool.

Q5 : Are there other load balancing logics I can avail on if I were to adopt a Multi CDN setup?

Of course there are, and we’ve seen a number of these over the years; these are to be seen as complementary and not as exclusive (you can factor in more than just one logic). Think about the following use cases:

1. You have a specific commitment with a given CDN, so after you exceed it you want to serve traffic over another, probably more cost-effective one.
2. Your traffic and Business mostly happens during a specific time frame, outside that timeframe you serve traffic over a less performant but more cost-effective CDN.
3. You are a Streaming Customer, therefore you are not as much interested into low Response Times as you are into Throughput and faster Stream Startup Times.
4. Your Origin Infrastructure is so good and performant that you don’t want to use a CDN in areas of proximity of your DataCenters, so you only serve traffic via CDNs into remote areas.

This is by no means an exhaustive list of scenarios, but rather more of a way to pick your mind around typical use cases we’ve come across over the years.

If you have any questions about how we can help you choose and implement a multi-CDN, contact us today to help you out with your performance and security needs.