A Quick Guide to Multi-CDNs: What to Consider, What Kind to Deploy
February 18, 2015 | Noe Garcia
According to market estimates, the CDN market will grow to $12.6 billion by 2019, with North America expected to be the largest in terms of revenue contribution. (As of 2014, the CDN market was at $3.71 billion.)
What does this have to do with multi-CDNs? Quite simply, the need for quick content delivery is growing. Whether that content comes in the form of an image, video, audio or other data file, consumers want content and they want it now. Multi-CDN strategies ensure that content gets to people as quickly as possible, 100% of the time, across every continent.
However, this assurance is just one benefit of a multi-CDN strategy. It also doesn’t allude to some of the complexities of multi-CDN strategies we’ll cover below. Before we cover the pros and cons of multi-CDNs though, let’s briefly go over what they are.
What is a Multi-CDN?
Multi-CDN describes the practice of using more than one CDN provider in order to further improve latency and uptimes on a global scale. While one CDN may be enough in a certain locality, a site owner may choose to implement further CDNs that have data centers in geographical areas where the main supplier isn’t highly represented.
Different CDNs tend to vary in performance in different areas, and some may offer a better service in video optimization, for example. Choosing a multi-CDN strategy is a fairly new practice that’s becoming more common as businesses have become more familiar with the technology.
One reason businesses choose multi-CDNs is so they don’t have to put all their eggs in one basket. While one supplier might offer 100% uptime, choosing more than one supplier means having a fallback should any supplier suffer an outage. The illustration below is an example of a multi-CDN that contains three different networks:
As you’ll see below, there are two ways to go about implementing a multi-CDN strategy that will garner you a network similar to the one illustrated. One way is more automated (the aggregator) while the other way is more hands-on (load-balancer).
Why Use a Multi-CDN?
If you have a website that serves minimal traffic, it’s unlikely you need a multi-CDN. The use of multi-CDNs has risen in recent years for those companies that find their site experiencing huge amounts of traffic on a global scale. These companies include media sharing/streaming startups, well-known brands, and large publishing sites.
For an idea of what websites use a multi-CDN and which ones don’t, take a look below at Bizety’s findings:
|World of Warcraft||3 CDNs|
As you can see, if you’re a growing video streaming company or social platform, it’s advisable to use a multi-CDN strategy. But as Bizety points out, as an e-commerce platform, it’s unlikely you’ll need more than one CDN unless you’re as large as eBay. For instance, Buy.com (Rakuten) is one of the largest e-commerce platforms and still only uses one CDN.
But if you do need more than one CDN, how do you go about creating a multi-CDN strategy? Right now you can take one of two directions.
Two Multi-CDN Strategies You Can Use
Depending on your content type, the size of your audience, and the size of your technical team, one multi-CDN strategy will be better for you than the other. First, let’s cover the type that’s good for a growing company with a smaller IT team.
Using an Aggregator
This approach uses just one service provider that combines, or aggregates, individual CDNs for you so you can manage them through one control panel. There are obvious benefits to this approach, the clearest being that administration is cut down.
However, while you might have an integrated service, this doesn’t mean that the various CDNs will respond in the same way. For instance, one service provider might complete instant purges while another might take minutes, even hours.
|Single control panel allows for easier CDN management||Can’t manage control panels of individual CDNs|
|Good for companies without in-house web performance person or team||Limited control for teams with developers who want to customize CDN|
|Bottom line: Easy to use||Bottom line: Hard to customize|
Example of Aggregator: Turbobytes
Using a Load Balance Service
The other approach you can take is to purchase each CDN through specific, separate suppliers and use a load balancer to efficiently distribute traffic between them. Based on where users are requesting content from, either CDN #1 or CDN #2 would be used, assuming you’re only using two CDNs.
For instance, say you’re an online publisher with a growing user base in China because you recently started translating all your English articles into Mandarin. While your main source of traffic still comes from North America, you want to please your growing China base with faster page load times. You’re already using MaxCDN that delivers content fast to users in North America and Europe. But because you have outgrown our Hong Kong edge due to exponential China growth, you decide to include a China-focused network in your CDN mix.
At this point, you would implement a load balancer. With this in place, the China-based CDN would deliver content to your users in most areas of China and Asia while MaxCDN would continue delivering content to users in all other parts of the world.
|Total control over what CDNs are used in your multi-CDN strategy||Higher cost to maintain, depending on what and how many CDNs are used|
|Unlimited opportunities for optimizations and developer configurations||Not ideal for companies without an in-house web performance team|
|Bottom line: More control||Bottom line: Resource-intensive|
Difference Between Federated CDNs and Multi-CDNs
Some CDN providers use the terms “federated CDN” and “multi-CDN” interchangeably when in fact they are not the same thing. Essentially, multi-CDNs are geared toward customers while federated CDNs are geared toward service providers. Where a publisher might turn to a service provider (hosting provider or CDN) that relies on a federation, a service provider would turn to a federated CDN to expand their infrastructure.
Confusing at all? Let’s break it down a little more.
As discussed, a multi-CDN is one which uses more than one service provider in order to further balance load. A federated CDN, defined by Cisco, is something that has “multi-footprint, open CDN capabilities built from resources owned and operated by autonomous members.”
In simple terms, this means that several "autonomous members" (i.e. service providers like CDNs, hosting providers, cloud application providers, etc.) pool resources in order to offer a powerful and wider-reaching product. These have emerged recently due to the increase in volume of both traffic and content.
Federated CDNs are intended to:
- Allows members to sell CDN services that reach a worldwide audience
- Allows service providers that don’t solely focus on CDN (managed hosting providers, app performance service providers, etc.) to create a content delivery network
- Simplify business and technical arrangements with service providers
- Provide an interconnection model between content and service providers that offers caches closer to the end user
- Take advantage of service provider investment to meet next-generation video requirements
Bottom line: Federated CDNs are for service providers looking to "build their own CDN" with third-party resources that are already in place.
Single CDN or Multi-CDN?
Even if having a multi-CDN as a failsafe sounds attractive to you, it’s important to consider the possibility of added complexity. This complexity has less to do with billing and more to do with having too many options (load balancing) or too little options (aggregator).
Yes, somewhat ironically, not having enough options can be complex, especially for companies with competent DevOps teams. However, if a DevOps team is nonexistent, this type of complexity can quickly turn into added simplicity.
If you adopt a custom approach to implementing a multi-CDN, it’s important to consider what ROI you may gain from this. In order to properly manage a multi-CDN through multiple suppliers, it’s often necessary for your DevOps team to ensure that what’s implemented on one CDN is on another. This can also go the other way though: What’s implemented on one CDN may not need implemented on another, thereby requiring thorough CDN documentation.
Above, we uncovered the pros and cons of various multi-CDN strategies. Let’s use that same approach to determine where single CDNs and multi-CDNs are most needed.
|Use a single CDN if:||Use a multi-CDN if:|
|The majority of your traffic comes from certain areas and isn’t evenly distributed worldwide.||Your traffic comes from all over the world that a single CDN can’t support.|
|You’re starting to gain an audience.||You have a huge global audience.|
|You’re an e-commerce platform.||You’re a video streaming company.|
|You want full control over your CDN, but not ready to invest in additional CDNs and software.||You need multiple CDNs and want full control over them (load balancing), or you want benefits of multi-CDN and don’t care about full control (aggregator).|
|You are currently using a single CDN and can easily scale without having to pay outrageous fees.||You exceed usage limits with current provider and want to offload overages to other CDN.|
Whatever You Choose, Consider Performance Holistically
Before you decide to implement a multi-CDN, it’s wise to carry out a complete site audit to ensure you can’t improve speed in other ways. If there are inherent issues with your site technologically, it’s unlikely a multi-CDN strategy will help you in any significant way. One way to test your website for performance errors is with these performance testing tools.
With that in mind, you should look at the site structure and its code to pick up common perfomance problems, which include:
- Under-optimized images
- Bloated and poorly written code
- Use of Flash over HTML5
- Used of expired code snippets for tracking services like analytics
- No GZIP compression
- Poorly constructed Expires or Cache-Control in header
All of this can be addressed by a good web development team. You can then add a CDN in order to take the strain off content such as images to ensure it performs at its peak. To make sure your website’s performance is up to snuff, go ahead and pass our backend optimizations and frontend optimizations articles off to your developer or system administrator.
A multi-CDN is rarely necessary for sites that don’t deal with a lot of content, but can be useful for those looking to enter other markets that their current provider doesn’t cover. It depends completely on the type and volume of content on the server, as well as the amount of traffic that the site receives.
Many business sites don’t need a multi-CDN, and while it’s tempting to implement a failsafe, the costs and administration involved rarely provide any ROI. For those larger sites that do need a multi-CDN, they do of course increase speed and reduce risk. But in order to implement, sound planning and research should first be undertaken to identify the correct multi-CDN strategy.
Bottom line: If your company is growing rapidly and delivering rich media to thousands on a global scale, it may be advisable to adopt a multi-CDN strategy.