What is a Multi CDN?

For us to understand what Multi CDN is, we need to take one step back and look at what is CDN first. CDN, is a geographically distributed network of edge servers with the goal of providing faster and reliable internet content delivery. CDN does this by caching internet contents at the network edge, hence reducing the physical distance between the source of data and the end-user.  

Multi CDN, as the name implies, is a strategy and a solution that leverages multiple CDNs from different CDN providers. With Multi CDN, this will allow you to use a large network of PoPs, not just from one CDN provider, but from multiple CDN providers. Hence, this will further improve the speed of content delivery, expand to wider regional and global coverages, and eliminate cybersecurity risks and outages. 

While load times are improved when users access websites served by a nearby CDN’s point of presence (PoP), those benefits do not extend to end-users located farther away from the CDN’s PoP. In other words, a single CDN doesn’t necessarily have PoPs in every part of the world, and this will result in varying performances of different CDNs in different areas. There will always be an area where some single CDN providers will not have the infrastructure to provide services in that particular area.

However, maximizing global presence and performance are must-haves. This is true not only for big companies, but also for companies who plan to expand their market in other regions. Hence, for a company to reach these goals, it is essential to tap on the combined regional coverages of multiple CDN providers to achieve a wider global presence.

In addition, a single CDN provider on its own can offer plenty of cybersecurity features and tools to protect your website from hackers. However, even with such cybersecurity features, single CDN providers are still vulnerable to outages, causing downtime for everyone who relies on their services. Examples of such are Cloudflare’s and Fastly’s outages. 

Ideally, websites should be available to users free from interruptions and outages. Hence, minimizing or eliminating the risks from cyberattacks and outages are very essential. By having a Multi CDN setup in place, this will provide a higher level of security redundancies. In case one CDN provider’s network goes offline, content can still be delivered from alternative CDN providers. 

Although a Multi CDN strategy is a fairly new practice, it is becoming more common as businesses have become more familiar with this technology. When you Multi CDN strategy, you can be ensured that end users from any part of the world will be able to access your website content and applications, and your business will be shielded from service degradations, cyber attacks, and outages. In addition, delivery over a multiple CDN architecture is considered to be a best practice for modern Ops teams. Ensuring uptime and multiple delivery contingencies give Ops teams peace of mind and the ability to reduce the adverse effects of vendor lock-in. 

Multi CDN core benefits

With the growing demand for streaming video, online gaming, and downloadable files; and with increasing expectations from a customer on the quality of experience (QoE), these put pressure on online businesses to rethink their content delivery strategies. 

Many businesses already rely on CDN to power their website performance and to improve reliability. Indeed, CDNs are the invisible backbone through which businesses can deliver valuable content to their target audience. However, businesses can still step up their content delivery strategy by upgrading to a Multi CDN infrastructure. 

With Multi CDN, businesses can manually or automatically set up their traffic to be routed according to location, availability, latency, bandwidth capacity, and even cost, while ensuring uninterrupted uptime and wider global coverage. 

Below presents a list of the core benefits of implementing a Multi CDN solution: 

1. Improved global coverage and performance. Single CDN performance can vary in different regions, but Multi CDNs spread across several regions, hence improving global latency and availability. An online business may be using a local CDN that works well in the US and EU, but struggles to deliver content in growing markets like Nigeria or Philippines. In addition, some premium CDNs might have limitations delivering content to regions with strict regulations, such as China and Russia. Multi CDN strategy can help companies expand their geographic reach to a wider range of areas where a single CDN does not cover, while also mitigating issues regarding regional regulations. In addition, Multi CDN also allows granular control of their content delivery, making sure that latency is at its absolute lowest in their specific target area, even all the way down to the city level.
   
2. Uninterrupted uptime. While large CDN providers are capable of operating in large commercial networks, they do not have unlimited capacity. Also, historically, even the largest CDN providers experience unexpected regional or global downtimes. Depending on circumstances, these issues can sometimes cause serious havoc to businesses. Good thing, Multi CDN is innately built with redundancies in its infrastructure. If one CDN gets overwhelmed by large peak traffic or experiences outages, Multi CDN can intelligently route web traffic through another CDN. This means Multi CDN can guarantee a 100% service uptime. Web content delivery will not be affected by traffic spikes, fluctuations, or outages, and will remain uninterrupted and running.
   
3. Improved user experience. According to statistics, if a website takes more than three seconds to load, more than half of the web visitors will leave that website (i.e. ~50% bounce rate). Aside from user web visits, retaining visitors is another important consideration. If your business rely on delivering large amounts of cacheable content (e.g. video streaming, downloadable files, etc.), or any contents that may cause big spikes in demand (e.g. product launches, or special events), users will definitely expect that they will be able to access the contents and services immediately. Customer acquisition and retention on a global scale, can be a very arduous task for a single CDN. Since Multi CDN intelligently distributes traffic to several CDNs, the content will be served from the fastest or better performing CDN. Multi CDN not only improves website loading time, and also ensures optimal delivery of large web contents and services.
   
4. Enhanced web security. CDN by nature hides away the original IP address of your host server as it functions as a reverse-proxy. This feature “shields” your website’s hosting infrastructure (i.e. origin server) from potential attacks like DDoS attacks. With Multi CDN, there will be additional security redundancies. Say for example, if a single CDN is compromised by a DDoS attack and took out a number of websites relying on that CDN, Multi CDN can easily mitigate this attack by routing the traffic to an uncompromised CDN, even before the DDoS attack can completely take out the attacked CDN. Basically, Multi CDNs not only offer redundancies for improvement in web performance, it also offer redundancies for enhancement in web security.
   
5. Optimized Cost. Both single and Multi CDN allow businesses to save bandwidth cost, but depending on circumstances single CDN can cost more. For example, different CDN providers have variable pricing for different regions of the world (i.e. pricing for peak vs. off-peak hours, volume, etc.). By using Multi CDN the traffic can be diverted to another CDN before the CDN exceeds its overage level or if there is an unexpected traffic surge. Another example is, for global-scale businesses, if a CDN for cross-region content delivery is not optimized, overflow of traffic on that CDN may cause an explosion in overage fee. Multi CDN allows businesses to optimize their bandwidth costs, regional content delivery cost, and overage fees, hence substantially reducing cost
   
6. Better Flexibility. Instead of being locked into a single CDN provider, businesses can have more flexibility when using Multi CDN, with the purpose of either to improve website performance, to expand global coverage, to spread risks across the board, or to avail a specific functionality for a given period of time, or combination of the above-mentioned. Businesses can always switch back and forth between their multiple CDN to address different circumstances. Flexibility is one of the aspects of Multi CDN which a single CDN lacks, and it is also a very important factor to mitigate risks of technical reason.

How does Multi CDN work?

After understanding what a Multi CDN strategy/solution is, and after knowing its advantages, we are now ready to understand how Multi CDN works. There are many ways to manage and operate a Multi CDN strategy, the following are the most commonly used methods:

Method 1: DNS load balancing

There are a couple of DNS providers on the market that manage a collection of customer-provided CDNs and use pre-defined traffic routing rules to direct traffic. This Multi CDN service is the most basic option for most companies. However, there is a need for the customer to subscribe to CDNs one-by one via individual CDN platforms. The more platforms they subscribe to, the more contracts they have to manage. Once the customer subscribed to all the CDNs they needed, the DNS provider will copy the CNAMEs of all the CDNs in the DNS record and then they will manage the traffic of the CDNs based on several traffic routing rules.

Here are some of the most common traffic routing rules:

• Round-robin – CDNs “take turns” serving content delivery to spread the load across activated CDNs. This method doesn’t take any factors (e.g. geographic location, network performance, etc.) into account, it simply distributes traffic to all CDNs equally.
• Weighted round-robin – Also known as “ratio load balancing”. Instead of equally distributing traffic across all CDNs, this method assigns priorities to specific CDNs, measured in “traffic load ratio” to route traffic accordingly. For example, you can set 90% of the traffic load to CDN A, while 10% to CDN B.
• Geolocation – This method distributes traffic based on the user’s location, and finds the closest PoP/CDN to distribute the traffic. It will dynamically activate the CDN closest to where the traffic originates. Location can be defined down to the country or even city level.

How it works

1. When a user visits www.test.com, this triggers a DNS lookup.
2. The DNS will determine which CDN CNAME to use based on the traffic routing rules.
3. The request will be directed to the designated CDN.
4. The user will now access www.test.com via the designated CDN.

Method 2: Primary-Fallback Scheme

Few CDN providers are starting to acknowledge the fact that unexpected large peak traffics and downtimes are inevitable. Some providers offer a primary-fallback multi CDN service. CDN providers usually designate their CDN network as the “primary CDN” and add another extra CDN provider/s as “fallback CDNs”.  In case the primary CDN experiences performance issues, they will route the traffic to the “fallback CDNs”. The good thing about this Multi CDN service is that the companies can maintain their primary provider relationship while still benefiting from the advantages of Multi CDN.  However, there will be an obvious bias in routing traffic through the primary provider. With such bias and limited flexibility, this will affect the overall quality of experience (QoE), functionality, and most especially pricing. 

How it works

1. When a user visits www.test.com, this triggers a DNS lookup.
2. The DNS will obtain the CNAME of the primary CDN (or the fallback CDN if the primary CDN experiences a problem).
3. The request will be directed to the primary (or fallback) CDN.
4. The user will now access www.test.com via the designated CDN.

Method 3: Performance data-driven load balancing

Some DNS providers offer this service to push Multi CDN to the next level. This method is somehow similar to the “DNS load balancing method”, wherein the service is performed on the DNS level and that the customer also needs to subscribe to CDNs one-by one via individual CDN platforms. However, the difference is, instead of simply adapting pre-defined routing rules, it makes decisions automatically based on actual CDN performance data. In this method, the DNS provider utilizes real user monitoring (RUM) and synthetic monitoring to gather performance data to make routing decisions. This method ensures better routing performance and better user experience than the DNS load balancing method.

How it works

1. When a user visits www.test.com, this triggers a DNS lookup.
2. The DNS will measure and analyze user geolocation, CDN latency, and CDN availability.
3. The DNS will obtain the CNAME of the best performing CDN for the user, 
4. The request will be directed to the best performing CDN.
5. The user will now access www.test.com via the best performing CDN.

Method 4: Turnkey Multi CDN platform

This is pretty much like the “performance data-driven load balancing service”, but since it is a dedicated Multi CDN platform it provides a marketplace-like experience, which gives customers the power to activate (or deactivate) and manage any CDN easily based on performance and at any point in time with few clicks of a button. The platform will already make subscriptions on the customer’s behalf, hence eliminating the hassle of negotiating and subscribing to CDN providers one by one. 

In addition, since the data-driven load balancing is done on the system level (not on the DNS level) this can provide customers a greater control on the routing decisions. WIth the platform’s unified controls and analytics, the customers can also have access to the real user monitoring data, synthetic monitoring data, and other tools, and use these to customize the routing decisions. 

WIth more CDNs available on the customer’s hand and with greater controls, the customers are ensured that the traffic will be intelligently routed to the best-performing CDN anywhere around the globe. Given the same reason, this method provides even much better routing performance and it is also considered to provide the best quality of experience (QoE) for the customers.

How it works

1. When a user visits www.test.com, this triggers a DNS lookup.
2. The DNS will obtain the CNAME of the Multi CDN platform’s system
3. The request is directed to the platform’s system via the platform’s CNAME.
4. The system will measure and analyze user geolocation, CDN latency, and CDN availability.
5. The system will obtain the CNAME of the best performing CDN for the user.
6. The request will be directed to the best performing CDN.
7. The user is now accessing www.test.com via the best performing CDN.