Original source: Limelight Networks
A Content Delivery Network is a system of geographically dispersed servers that facilitates the delivery of digital content with high performance and high availability. The idea behind a CDN is to move content closer to end users. Instead of centralizing digital content (web applications, web objects, files, downloadable media and streaming media) on a relatively small number of servers, the content is cached across many servers distributed around the globe. End-users now retrieve the content they’re looking for from the closest CDN edge server rather than going all the way back to the origin to retrieve it. A CDN can also instantly create a TV broadcast-quality experience while converting live streams on-the-fly into the right device formats. This results in much better performance (lower latency) for your customers. It also avoids overloading your origin and allows your audience to scale.
There are several reasons to consider a multi-CDN strategy:
Availability: While an outage may not rise to global notoriety, it’s likely just as devastating for your business. As the Internet has become more critical to every aspect of business, minutes of downtime can impact your bottom line and damage customer relationships. Multi-CDN can minimize single points of failure by providing alternate delivery options during an outage.
Performance: It’s unlikely that any single CDN delivers the best performance for all traffic types in all regions all of the time. By intelligently balancing your content delivery needs across multiple CDN providers, you can mitigate the impact of specific providers' performance glitches in specific regions for specific traffic types.
Capacity: Large-scale content delivery events may create choke points in individual CDN providers or in certain locations. Multi-CDN alleviates these bottlenecks by distributing load amongst multiple CDNs. For large live events such as the World Cup, rapid scaling is a critical function of CDNs. If a match is tied near the end of regulation time, there are usually massive spikes with fans logging in to watch the final minutes.
Security: Having multiple CDN providers allows you to minimize exposure or bypass compromised CDNs altogether in the event of a cyberattack.
In many situations, multi-CDN can be beneficial, but how does one deploy multiple CDNs, and what factors should be considered in determining the best method for your particular application?
DNS: The Domain Name System (DNS) is a naming system for the Internet. However, the Internet equipment doesn’t understand domain names – it operates using IP addresses. DNS performs the translation from the domain name into the IP address. DNS is one of the most prevalent switching methods between different CDNs in a multi-CDN environment.
Static: The most basic method of incorporating multiple CDNs is modifying DNS entries. This method can be used in an active-standby configuration. For example, if one CDN fails, the DNS entry is modified so that all requests are redirected to another CDN. Using this method, mapping different hostnames can enforce different policies to different CDNs.
Weighted Round Robin: The weighted round-robin approach allows you to apply a different ranking to each CDN to indicate CDN preference. Weights or ratios can be based on criteria you determine most important for your business, e.g., cost, performance, ISP connectivity, etc.
Geolocation: In the Geolocation case, traffic is distributed between CDNs based on the end user’s location. This allows you to favor specific CDNs based on where traffic originates.
Performance: Performance-based load balancing considers current network conditions to achieve the best theoretical performance. This approach involves measuring network conditions and considering this data when balancing decisions.
Multi-CDN has some compelling benefits, but it is not necessarily for everyone. Ask yourself these questions when considering if a multi-CDN strategy is right for you: Can you afford minutes or hours of downtime? Do you have traffic spikes that could be alleviated with an overflow capability to other CDNs? Are your digital content delivery needs performance-sensitive? Is your audience distributed across the globe? If your answer is yes to these questions, multi-CDN may benefit your organization.
Once you have determined that adding a CDN to your content delivery environment makes sense, the next question becomes which CDN partner to select. Here are some important factors to consider:
Geographic coverage: Important questions to consider: where are your users located? Where are you looking to expand? Look for a CDN with a presence in the regions or countries where most of your users are. When considering your global traffic distribution, it’s also important to consider future growth. If you expect to see increased traffic coming from emerging markets like India, for example, the factor in your decision now is to avoid having to renegotiate your CDN contract or prematurely move CDN providers. Look for a CDN with a presence in places where most of your current and future users are.
Performance metrics: may sound obvious, but the best place to start is by considering what is most important to your customer's experience. In this case, important metrics for video delivery might include rebuffer rate, bit rate and startup time.
Performance measurement: There are several performance monitoring tools commercially available, however, in many cases, results can be misleading. The best approach to evaluate performance is to do a trial or proof of concept with one or more CDNs, using your actual workload in the geographical regions that are most important to you.
Service and support: Things sometimes go wrong or you may want to tap a technology expert. At times like this, excellent support can make all the difference. Consider how important it is to have access to live customer support. Will that support be available outside of business hours? What kind of support is offered in your region? Is the support free or is there a premium charged for this service? If you deliver live events, what relevant experience does the CDN partner have and are they willing to participate on a bridge before or during the event? Can the CDN vendor assist with onboarding or migrating from another CDN?
The bottom line: Using multiple CDNs to deliver these digital content experiences promises even greater levels of availability and performance. By leveraging the right combination of providers, and enterprises, you can simultaneously improve end-user quality of experience while lowering costs. See Limelight’s 5 Things You Need to Know About Implementing a Multi-CDN Strategy for more information on this topic.
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