At the surface, all content delivery networks, or CDNs, have the same features and functionality. They all deliver static images, data and video. They can optimize and accelerate traditional data-oriented applications, as well as newer video-oriented applications and services. Most will provide some level of security, and virtually all will state their services are offered globally.
But dig a bit deeper, and you'll likely find significant differences in what CDN vendors offer. The very nature of CDNs makes every decision for a new service an expensive one, as new service typically requires software development. But with CDNs, the cost doesn't end with software development. Almost every new service requires extensive and expensive hardware to be rolled out and maintained at dozens, if not hundreds, of locations worldwide.
Given this level of commitment and expense, it's unlikely you will find CDN vendors competing head-to-head in every possible service area, because they simply can't afford to do so. To identify which CDN provider is right for you, you need to be able to read between the checkboxes and understand the details of key features. This article is designed to help you map detailed features to your company's needs.
Given the sheer number of individual features advertised by CDN vendors, it's necessary to organize them into functional groups. While some vendors might group features differently, the following groupings should help you get a handle on the main feature and function areas.
Application delivery optimization
Advanced management and purging of stale content. CDNs offload work from customers' servers by delivering static content. But static content doesn't necessarily remain static forever. While built-in mechanisms ensure a periodic refresh of data from the origin server, many organizations need more control over when data gets purged and refreshed.
At a minimum, you will want to ensure your CDN provider offers a GUI to manage and purge stale content. Of course, more important than just having an interface is the level of granularity it provides. For example, can you purge content for a complete domain with one command? Are there commands that allow you to purge a subset of your content?
Does your CDN allow you to tag or label your content and use that as a method to specify a purge? The last thing you want is to have to purge stale content one object at time.
Certain customers may need rapid and sophisticated content purging. The answer to such a requirement is program-level access to purge functions. Some CDNs provide an API that enables this program-level access to content purging. API-based purge management requires you to write a program to control the purge functions, but undoubtedly provides the most control over this important function.
Image optimization and management. Images such as JPEGs, PNGs and GIFs constitute a significant part of many applications. While they can add to the visual attractiveness of an application, images can also be problematic.
High-resolution images can be several megabytes in size and take significant time to transmit to the client. This can be particularly vexing for mobile users. Not only do they have to wait for content to load, but the high-resolution images can eat into their cellular data allocation. Worst of all, their devices might not even be able to display the image at the downloaded resolution.
To get around this issue, many CDN providers offer some type of image optimization. The most commonly used feature will be optimizing images for a particular display device -- that is, sending lower-resolution images to mobile devices with small screens. Some CDNs offer more sophisticated options for managing images, including watermarking, face detection crop and entropy detection -- where software detects and crops the image so the most interesting elements are highlighted.
Some image formats are highly compressible. Some CDNs also provide dynamic compression of images on transmission to reduce load time.
File storage. Some, but not all, CDNs enable you to use their service as cloud storage to store entire files. This can be an important feature to customers who need an efficient offload strategy for storage and delivery of static files. If your company delivers software updates, data files or other relatively static data, such as product catalogs, this feature could be of interest to you.
Video delivery optimization. When it comes to consuming disk storage and delivery bandwidth, video is king. If your business product is video or you use a great deal of video to support your products, this will be an area of great interest to you.
In our research and discussion with CDN vendors, we found significant differences in this area. Some vendors consider video just another type of file to deliver, whereas others provide sophisticated workflows for handling video.
If video is important to your company, first determine whether your needs are limited to delivery of previously recorded video on demand (VoD), or if you also need to deliver real-time, live video, as the support and workflows will be different.
For streaming video, it's important to understand the scope of transcoding services. In the best case, you will provide a single video source file to your CDN provider, and the CDN will transcode the file into the various popular delivery formats.
Livestreaming can use several different formats. Video delivery formats of interest can include HTTP Live Streaming, MPEG-DASH, Microsoft Smooth Streaming and HTTP Dynamic Streaming.
Many companies want their live video to be available as VoD following the live showing. Some CDNs provide a workflow to create VoD automatically.
For clients that monetize video delivery, some CDNs provide for server-side ad insertion into streaming video. Some vendors even provide on-the-fly closed-captioning and multilanguage subtitles. These more specific needs, however, are typically supported by only a few CDNs.
While reporting and analytics are important elements of every feature set, the sometimes-viral nature of video makes analytics especially important. It's important to be aware of the nature and level of granularity your CDN can provide into the viewing audience of your video content.
Content security. Many companies monetize their web-based content. For those companies, content security is an important feature area. Multiple systems and methods are available for offering content security, and content security should be considered a general, umbrella term. It's important to identify your company's specific needs and the CDN's specific capabilities when it comes to content security.
Digital rights management. DRM ensures only licensed users can play or download protected content, such as audio, video or text. Because there is no universal approach, you will need to drill down and determine which formats, if any, your prospective CDN supports. Popular DRM protection systems include Apple FairPlay, Microsoft PlayReady, Google Widevine and Marlin DRM.
Geoblocking. Here, the CDN identifies the geographic location of the client by their IP address and can block based on customer specifications. For example, if a music video is only licensed for delivery to North American markets, a request from a user whose location is determined to be in the U.K. will be blocked.
Ad-blocking neutralization. This is a bit of an oddball feature because of its relationship to content more than any relevance to content security. In short, this feature blocks the blocking of advertisements. Users don't like to see ads, but many services make their money by displaying ads. So, this feature allows ads to make their way through to users, which benefits advertisers and the platforms displaying the ads.
Using extensive research into the content delivery network market, TechTarget editors focused on 10 leading providers of shared global content delivery network services. Our research included data from TechTarget surveys and reports from research firms, including Gartner and Forrester.
CDN traffic management
The business of CDNs is traffic, so it makes sense some features focus on this area.
Application load balancing. Application load balancing is conceptually the same as load balancing and application delivery controllers in a stand-alone enterprise deployment. The CDN contains intelligence that can direct traffic to different back-end servers based on various criteria. Local load balancing references a pool of servers located in the same point of presence (POP) or data center. Global load balancing expands the pool of back-end servers to include servers in the other CDN's POPs.
Origin shield. This places another CDN server between the cache at the edge of the CDN and the customer's original content server. The idea is when content can't be pulled from cache because it isn't there or has expired, the request can attempt to pull the data from the origin shield server, rather than having to forward it all the way to the customer's origin server. The origin shield server acts as another layer between the internet clients and the customer server. This feature reduces origin server load, saves bandwidth and reduces delivery time to the end client.
Domain name system (DNS) services. A key part of traffic management is ensuring traffic takes the most efficient path, which usually means the shortest path. With CDNs, DNS services can direct traffic most efficiently, functioning similarly to application load balancing. Because the CDN is aware of your server and application configuration, it can make more intelligent decisions than just simply resolving a name with an IP address.
Network security. Because the CDN serves as a focal point for customer traffic, it makes sense for the CDN to also provide network security functions. Not only does this stop sooner, but CDN-based network security can supplant the requirement to have extensive and expensive network security hardware at every customer location.
Distributed denial-of-service protection. DDoS attacks use a flood of traffic to effectively deny legitimate users access to an application. DDoS traffic can not only use up most of the bandwidth available to the target, but depending on the attack, it can also force the target to waste CPU and other resources in processing the attack traffic. DDoS protection products monitor incoming traffic for attack patterns. Once detected, the attack traffic is intercepted and discarded. Thus, both bandwidth and server resources are preserved for legitimate use.
Web application firewall. The WAF is the logical next step for security beyond network-level threats. Many security threats are more sophisticated than brute-force DDoS attacks and use application flows to attempt to compromise target systems. For example, attackers frequently try to find holes in SQL or other database flows that can be used to run data-gathering commands that will harvest data illicitly.
Today, WAFs might look not only at data and flows going in, but flows going out, as well. Should malicious software or a malicious user get inside, data could be exfiltrated without an inbound attack. Data loss prevention is now a part of the WAF lexicon and needs to be considered.
Rate limiting. This could be listed under traffic management or network security, as it relates to both areas. For reasons of performance or security, the CDN can monitor flows and limit the traffic rate of a given session or IP address. This can be done to conserve network bandwidth and server resources for other users. In addition, excessive demand for bandwidth could be considered a DDoS attack, and rate limiting can reduce the negative impact of that traffic on other users.
Bot detection and protection. Bots are nonhuman users that interact with websites and other internet resources. We often think of bots in negative terms, but they aren't necessarily bad and have been around a long time. Search engines use bots to crawl the web and build up the search indices we all use to find information. Bot detection and protection features allow users to identify nonhuman users and, depending on the CDN service, control resources that bots can use.
Secure Sockets Layer. SSL, in past years, was found mostly with e-commerce transactions and websites. In recent years, Google has made a push for all websites to use SSL or otherwise be identified as possibly unsecure. So, SSL is an important consideration. CDN providers can offer a number of options with SSL, including forcing a session to use a more recent, more secure level of SSL.
Geographical considerations for CDNs
Presence. Once you create your list of key feature requirements and build your shortlist, presence is probably the next item on which to focus. Simply put, you want your CDN provider to have resources in place at the edge near where your users are based.
Because it doesn't take much for a CDN provider to declare presence in a particular geography or country, you will need additional detective work to find out if your CDN vendor's presence in, say, South Africa is a pair of servers sitting at an internet service provider or an entire data center.
For security reasons, many CDNs don't disclose specifics about their physical presence. Unfortunately, the security rationale also becomes a marketing cover that might allow some vendors to make it appear that their global presence is larger than it actually is.
You may need to sign a nondisclosure agreement with a prospective CDN to get the level of detail that you want and need to feel comfortable that its physical presence in a given region or country can meet your requirements.
China-specific service. China has requirements with respect to the flow of internet traffic that are typically more restrictive than in many other countries. If users in China represent a sizable or important part of your user base, you will need to comply with those requirements and have a CDN that complies, as well.
Some CDNs offer a China service on their own or partner with companies that have services that comply with the requirements of the Chinese government.
Other countries besides China may have unique requirements, as well as the internet, and data becomes more regulated. Thus, if particular countries are critical to your business, you should ask specifically about those countries and their requirements when narrowing down your selection of CDNs.
Storage location for information. Global CDNs store data all over the world. In the past, you might not have cared where your data was stored, but now it can be a significant factor. Privacy laws, especially in the European Union, kicked into high gear in 2018, with enforcement dates for General Data Protection Regulation going live.
The storage location of the data could determine which privacy laws come into play. As a result, it's important to determine whether your CDN provider will allow you to specify where your data is stored. The issue isn't just the data you store for consumption on the CDN; where the statistics and analytics collected from usage are stored can make a difference, as well.
Other relevant CDN features
We briefly mentioned reporting and analytics, but those are important considerations, as well. We've touched on APIs, but if you have sophisticated needs, you might want to get details on all the different CDN features and capabilities accessible via an API.
Some CDN deployments can be quite complex. If you want or need implementation help, some CDN vendors offer professional services.
While these other features and services might not tip the scale one way or the other, they can be important considerations.
CDN support and pricing
Cost and support options will vary depending on what services are contracted and the type of response time required. Support will vary by CDN provider and depend on your coverage needs and turnaround times. Email support and community support, such as a user forum, are often considered standard.
CDNs are sufficiently complex that it isn't easy -- or often even practical -- to try to get a simple answer to the question, "What is your pricing model?" Many content delivery network services are based on how much data is delivered. Other features might be priced on a per-user basis.