Multi-CDN: a solution for CDN outages

2022/04/05 | 8 mins

How different would the world be without the Internet? Recent incidents such as the Fastly Outage that took airlines, banks, stock exchanges, and trading platforms offline show these situations are not hypothetical; these are real-world problems. Therefore having a solution to handle CDN outages is crucial. One popular solution is a multi-CDN strategy.

The complexity of the "network of networks" that is the Internet is becoming more and more evident every day. Outages like Fastly are just one of the increasingly common service interruptions. Today, preventing billions of users from accessing their favorite social networks does not have to be the result of a cyber-attack. As demonstrated in the stunning global outage of Facebook, WhatsApp, and Instagram – all it takes is a "faulty configuration change" in the backbone routers to leave everyone in the dark for hours.

Obviously there is no definitive solution for preventing human errors or cyberattacks, but there are methods for minimizing their impact. This article will explore multi-CDN strategies, a solution that might be ideal for certain use cases.

What is a CDN?

Simply put, a Content Delivery Network (CDN) is a group of interconnected servers distributed across different geographic locations, each hosting a copy of your content.

The purpose of this type of deployment is that your content will be closer to your target audience in each geographic zone, which minimizes connection latency, improves bandwidth efficiency, and makes the user experience smoother and more rewarding.

However, despite its benefits, using a single CDN also has its downsides.

  • Connection performance. Performance for different CDNs may vary at different times of the day or perform better in specific locations. These types of fluctuations in latency can last for hours and have a negative impact on users.
  • Outages. As mentioned at the beginning of this article, CDNs are not free from outages. In these scenarios, your content will simply not be available, which completely eliminates the benefit of using a CDN in the first place.
  • CDN features. Not all CDNs are created equal. It is common for certain CDNs to be optimized for live video streaming while others focus on static content. This limits your ability to offer mixed content.

A multi-CDN strategy can help you avoid these negative consequences.

What is a Multi-CDN?

Imagine for a moment that you have a critical service that depends on a stable Internet connection. To provide redundancy in service, a possible solution is to use a multi-WAN setup that allows you to switch to different Internet Service Providers (ISP) as needed.

Multi-CDNs operate using the same principle. By having access to several CDN providers simultaneously, you can improve the performance of your website or application, benefit from the associated redundancy, and minimize outages.

Although the solution seems simple in theory, in practical terms, implementing a multi-CDN strategy has its challenges.

Understanding Multi-CDN strategies

In a world of cloud computing and networks, there are many ways to achieve the desired result. To this end, each multi-CDN strategy seeks to achieve the same goal, but focuses on different use cases.

DNS load balancing

This strategy consists of defining and implementing policies that distribute traffic among several CDNs using a Domain Name System (DNS) resolution. This type of DNS-based load balancing can be accomplished in several ways.

  • Round robin. Round-robin DNS load balancing uses a particular type of server called an “authoritative nameserver.” This server stores multiple “A” records for each domain that are tied to different IP addresses. When a DNS query occurs, these IP addresses are rotated in a round-robin fashion, distributing the requests among different servers, and thus preventing traffic from being routed to a single CDN.
  • Weighted round robin. This method is very similar to the conventional round-robin. It has the added advantage that it implements an algorithm that considers the health and latency of each CDN and directs the request to the most efficient CDN.
  • Geo-location. Another widely used strategy is to use an algorithm that distributes requests based on their region of origin. Thanks to this method, requests can be dynamically distributed by assigning the most appropriate CDN according to its geographic area.

RUM load balancing

While DNS load balancing helps to improve latency and optimize available bandwidth, it still has one major weakness: it only considers the load of the servers and not the user experience. Real User Monitoring (RUM) load balancing addresses this problem by collecting data about the end user session.

Since this strategy "measures" the end-user experience in a specific way, it allows traffic to be directed to the best performing CDN.

Turnkey Multi-CDN platform

Whether the multi-CDN strategy uses a predefined set of rules or an algorithm to allocate CDNs dynamically, your company will need to dedicate significant staff and resources to manage this service. Under a managed CDN strategy, you can delegate this task to a third party to manage everything. While this approach removes your control over the process, it offers multiple advantages.

  • End-to-end delivery solution. Experience in multi-CDN deployments is crucial. Suppose your eLearning site is not loading in China and your team does not understand how to fix this problem, or you need to know the speed of travel booking sites in and out of China. Having a team of experts managing your multi-CDN strategy while your team monitors the results allows you to make better use of your staff and resources.
  • Highly optimized. Reputable managed CDN services providers have extensive experience in managing and optimizing traffic flow. This gives you the possibility of enjoying industry-leading performance for your content delivery network in complex regions such as China.
  • Custom-tailored to your budget. One advantage that cannot be overlooked is this type of solution allows you to control your budget by making adjustments as needed. Moreover, top providers like GoClick China can guide you through everything you need to know about Chinese CDNs, which allows you to obtain solutions tailored to your specific needs.

Primary / Fallback CDN

Last but not least, some strategies primarily aim to create redundancies for your applications and websites. In this type of deployment, your company has a primary CDN responsible for delivering all your content and one (or several) backup CDNs. This type of strategy allows you to switch from one CDN to another during outages or when latency levels exceed established limits.

Benefits of a Multi-CDN

Regardless of the type of strategy you use, implementing a multi-CDN solution will benefit your organization in a variety of ways.

  • Redundancy. Undoubtedly the main motivation for implementing a multi-CDN strategy is to ensure the availability of your application or website 24/7. As evidenced by the recent Internet outages, no CDN is exempt from encountering bugs, attacks, or simply large peaks in traffic that affect the service. For this reason, the redundancy offered by multi-CDNs is important. In the event that one of the CDNs suffers a regional or global outage, the traffic can be diverted to another CDN to keep the services operating.
  • Unique value proposition. In addition to avoiding service interruptions, it is essential to consider user expectations. This is most evident in video streaming services requiring low latency to avoid ruining the user experience. Users demand smooth applications and web pages that meet expectations. That is a unique value proposition that many businesses overlook, especially in the Asia-Pacific region.
  • Avoid vendor lock-in. Vendor lock-in is considered one of the biggest problems in cloud computing today and is best avoided if at all possible. Deploying a multi-CDN gives you the advantage of not relying on a single infrastructure, giving you greater flexibility.
  • Geographic footprint. Regardless of the provider, be it Cloudflare, CloudFront, Fastly, Akamai, or any other industry leader – no provider can offer you the best performance for each and every region. One example is cloud hosting. Generally, providers have a larger number of data centers in a particular global region such as Europe, the United States, or Asia. The same is true for CDN providers. A benefit of multi-CDNs is that it allows you to integrate CDNs with proven performance in a specific region that is key to your business, such as China or any other Southeast Asian country.

Are Multi-CDNs right for You?

This article has highlighted the many benefits of multi-CDNs. However, does this mean that multi-CDNs are the ideal solution for all use cases? Certainly not.

As is often the case with cloud computing technologies, there are no perfect solutions. For this reason, before implementing a multi-CDN strategy, you should carefully analyze all scenarios and alternatives. Below we will analyze several aspects to take into consideration.

  • APIs. The flexibility and redundancy that multi-CDNs provide come at a price. Each vendor has designed their solution based on their own experiences of successes and failures, resulting in custom APIs that are not always compatible across CDNs. This diversity can be a real nightmare to manage, especially in determining the optimal configuration for each CDN provider.
  • Exit traffic. Due to the complexity of handling multiple APIs, IT departments are continually challenged to optimize the configuration to ensure that multi-CDN deployment has the best possible cache-hit ratio across all CDNs. This is not always possible, which results in you paying more than desirable amounts for the origin’s exit bandwidth.
  • Origin protection. Another challenge of employing multi-CDN strategies is preventing the origin from overloading. It is much easier to reach full capacity when serving massive amounts of content to different CDNs simultaneously. This is why it is often necessary to alleviate the load by using load-balancing services, like Fastly, as an origin for the other CDNs. This adds another layer of complexity to your deployment.
  • Security. One aspect that cannot be overlooked is the increase in attack vectors when using a multi-CDN strategy. Different CDN providers enforce different security policies, which means that a bug or attack that one CDN rejects can penetrate another. Therefore it is vital that your IT team is able to respond in a timely manner to avoid downtimes or slowdowns of your applications and services.
  • Storage. Storing your content in a single CDN is relatively straightforward. However, for a multi-CDN strategy, storing content becomes a challenge. Generally, you have to decide between replicating the content on each CDN or allowing one CDN to grant access to the origin to other CDNs.
  • Transcoding. Delivering Video On Demand (VOD) and live-streaming at scale requires serving countless devices simultaneously. This involves multiple sessions with different formats, bitrates, and encryption levels. Optimizing transcoding across multiple CDNs is a daunting task, which, if not done correctly, can introduce inefficiencies that will affect latency and thus create a negative user experience.
  • Cost. Cost for multi-CDN strategies is a double-edged sword. On the one hand, savings can be obtained by diverting traffic to a CDN that offers a lower cost during peak hours. On the other hand, if you serve video content, you may have to account for costs associated with storing of multiple versions of the same video in different formats, bandwidth access, and more. This makes managing the cost of a multi-CDN strategy a delicate balancing act between different requirements.

The points described above are just some of the most relevant aspects to consider before implementing a multi-CDN strategy, but that does not mean that they are the only ones.

Depending on the amount of traffic your content generates, the type of content, the size of your IT team, and where the majority of your audience is located, a single CDN may be a better solution.

The dispatch and centralized control mutual backup system based on multi-domain

Final thoughts

In this article, we have explored different aspects of multi-CDN deployments, ranging from their definition, load balancing strategies, and pros and cons. However, it all boils down to one question, is a multi-CDN solution right for you?

As you have seen, there are a lot of variables to consider. In fact, evaluating these variables is so complex that it is essential to seek assistance from professionals with extensive experience in this field to find an optimal solution for your specific business.

In this regard, GoClick China provides both single CDN and multi-CDN professional services and consulting. Unlike other providers that neglect the single point of failure that a multi-CDN strategy can have, GoClick China provides you with a custom API that assists you in selecting the best CDN at any given time. Our solution allows our customers to be highly resilient easily switching from a primary CDN to a backup CDN, thus providing an effective level of redundancy and failover.

If you are interested in exploring the possibilities of how to improve your website's performance and availability within the lucrative Chinese market, please consider our services.

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