Content delivery networks are critical links for delivering web and application data to end users. With the vast increase of rich media in recent years, CDNs went from a nice-to-have to a must-have for businesses and organizations of all sizes.
These networks of geographically distributed and interconnected servers improve the distribution of web applications and streaming media by reducing the distance content must travel to reach users in various locations. Since longer distances equal longer delivery times, companies risk losing customers and, ultimately, money if delivery takes too long as users move on to the next site.
One of the most significant advantages of a CDN in place is the ability for organizations of all sizes and vertical industries to use bandwidth more effectively, while reducing data center infrastructure and connectivity costs. Improved UX is the ultimate goal a CDN should achieve for a business speeding up content delivery.
Snapshot of the CDN market
The CDN market includes dozens of vendors, ranging from those with a global presence to those that specialize in a particular country or region. With the growing importance of rich media -- high-resolution images and video -- more CDN vendors focus on optimizing rich media delivery.
While media companies and software distributors were the initial customers, CDNs now are considered an essential tool across a variety of industries. Early CDNs focused on caching static content near the target user, but today's CDN services offer a wide range of capabilities, including streaming content, security and analytics.
With CDNs, organizations can offload content delivery to third-party vendors and avoid the costly task of building out their own infrastructure. The use of CDNs enables small companies to project a larger image to customers and provide secure, responsive and fault-tolerant connectivity to their customer base. Today's pricing models make CDNs viable, even for the smallest company, with pay-as-you-go options for something as small as a single blog.
CDN benefits continue to grow
While the services offered by CDNs have evolved over time, their fundamental purpose has not. CDNs focus on improving the end-user customer experience by providing high data transfer rates, coupled with low latency, resulting in better end-user response time.
Early CDNs functioned as the network edge for their customers. In the late 1990s, when the first CDN launched, content consisted of webpages, as well as GIF and JPEG images. CDN servers stored static content and delivered that data to end users on behalf of the origin website. This not only delivered content to the end user faster, but it did so without burdening the source company's data center and WAN infrastructure.
The CDN market also benefited from the massive growth in IT outsourcing. Years ago, IT managers were understandably reticent to trust CDNs to store valuable data outside the boundaries of the corporate-controlled IT environment. The enormous success of cloud platforms, such as AWS, Microsoft Azure and Google Cloud, has changed those perceptions -- whether IT managers like it or not.
The aforementioned cloud platform vendors now all offer their own pay-as-you-go CDN environments tightly integrated into their native architecture.
So, as the need for low-latency delivery of high-resolution video and images has increased, the technical and political barriers to entry for CDNs have come down.
As audio and video became popular web content, CDNs evolved to deliver it. And, as organizations became more comfortable with third-party, off-premises IT services, CDNs expanded further to provide a variety of functions -- from application delivery controller services, such as load balancing, to application firewall and other content and network security services.
Today's CDNs differentiate themselves by the types of services they offer, as well as the granularity and functionality of those individual offerings. For example, some vendors offer services focused on API management, where others offer advanced content security, digital rights management and geoblocking features. While all vendors offer caching services for static content, some have added sophisticated management features for purging and refreshing cached content.
Some vendors specialize in security, going beyond the basics to include high-performance distributed denial-of-service (DDoS) protection and bot protection. One security-focused vendor, Imperva, even offers a service-level agreement, which guarantees attack mitigation within just three seconds.
How do CDNs work?
CDNs function as generally transparent proxies for companies' services and web resources. Consumers are usually unaware they're using a CDN. Once they enter a company's web address, the graphical elements on that page are fetched dynamically from the CDN's cache -- not from the website's servers.
The CDN locates its content servers using a combination of its own dedicated points of presence and POPs run by other ISPs. To provide the best response time, the CDN usually interconnects its edges using dedicated private lines, rather than via internet links.
At the CDN edge, the customer request is inspected and processed. In the most common use case, the CDN checks the static web content for freshness before delivery. If a company uses a CDN to store customer-facing data files, such as product catalogs or software updates, those are fetched from the CDN storage servers and delivered. Video files stored by CDNs can be delivered and streamed directly to the customer without burdening the origin company's servers or the origin company's WAN.
Many CDN vendors also optimize the video and store different resolution versions in the CDN cache. This way, network usage can be optimized because the resolution of the video stream can match the resolution of the device displaying the video.
While it's good to know what CDNs do, it's just as important to know where they do it. CDNs are all about faster delivery, and a big part of that is reducing latency, which requires the CDN server be geographically near the end user. One of the first questions an organization should ask a prospective CDN vendor is where the CDN has POPs.
While most CDN vendors boast coverage on six continents, that presence isn't identical on all continents or in all countries. As a result, buyers must understand which geographical regions they will be serving data to before investing in any given CDN vendor.
What's driving increased CDN use?
CDN use has grown over the past several years, partly due to the increase in video as a common website element and business tool. Not only does video require a lot of disk storage in comparison to traditional web objects, like PDFs, video delivery places a significant demand on internet and WAN bandwidth.
As noted above, another important enterprise trend is the use of cloud-based applications and services. Some CDN services are beginning to compete with cloud providers by offering such services as video and data storage.
With the processing and delivery burden on the CDN's IT infrastructure, the burden is similarly reduced at its customers' own sites. This could translate into lower demand on existing IT and WAN infrastructure, reducing a CDN customer's Capex and Opex costs.
Key features of CDN services
CDN offload not only brings immediate advantages, but a beneficial ripple effect as well. Fewer servers are necessary with offloaded delivery, which means less physical real estate, power and cooling are required.
All CDNs offer core functions, such as delivering static, dynamic and often streaming and on-demand video. These services alone are often sufficient to justify using a CDN as companies can ensure their end users will benefit from rapid response times.
Even within the core delivery function, CDNs offer additional benefits. Some CDN vendors offer image optimization and management services. These services can dynamically deliver images optimized for a specific device, whether it's a desktop computer, mobile phone or some other device.
Many CDN vendors offer advanced security-related services, such as DDoS protection, web application firewall functionality and bot protection. Security-focused CDN services can reduce the burden on on-premises security hardware, thus extending its lifetime. For certain applications in industries such as finance and healthcare, CDN security features might be mandatory for compliance with government regulations.