Published: 23 July 2024
Contributors: Stephanie Susnjara, Ian Smalley
A content delivery network (CDN) is a geographically dispersed server network that enables faster web performance by locating copies of web content closer to end users or facilitating the delivery of dynamic content (for example, live video feeds).
Each CDN server is located on the "network edge"—closer to end users than the host server, where the website originates. For this reason, CDN servers are often called "edge servers."
Each server stores or caches copies of a subset of the web content—HTML files, images, audio, video, applications—from the host server. Caching, the process of storing files on the edge servers, brings files closer to the customers, decreasing the time it takes for the data to stream across the network, known as latency.
By reducing the distance between this content and users, the content delivery network helps the website publisher provide faster performance, reduce user loading time and control its own bandwidth cost and consumption.
Organizations typically purchase CDN services from CDN service providers that maintain their own server networks.
As previously noted, a content delivery network (CDN) works by helping a web publisher deliver faster, higher-quality performance for users through content distribution from servers closer to them than the website's origin server. An origin server is a computer or server in a physical location (such as a data center) that stores and computes content for a website or web page.
For example, suppose that your website resides on an origin server in the United Kingdom (UK). If someone from the United States (US) accesses your site, the CDN serves that user from an edge server in the US, closer to the user, instead of from your UK-based origin server for the web page. This edge server is a type of proxy server—sometimes called a cache or caching server—that acts as a gateway between users and the internet.
A CDN can deliver two types of content: static and dynamic.
- Static content is online content that remains constant on a website. It remains the same for all users who visit the site. Content such as website logos and brand information written in HTML are examples of static content.
- Dynamic content is online content that changes based on user behavior, location or other factors. For example, social media feeds (Instagram, Facebook and more), streaming platforms (Netflix, Hulu and others), and ecommerce sites (such as, Amazon) deliver media-rich dynamic content that’s tailored and personalized for each user.
DNS is part of the internet's standard protocol that allows users to access websites by using domain names and URLs instead of IP addresses. DNS is the phonebook of the internet; it simplifies the process of searching for specific websites through web browsers. Content delivery networks (CDNs) use DNS to keep track of and supply IP addresses for origin and edge servers and perform dynamic request routing.
A point of presence is a physical location that stores servers and routers in different regions worldwide. They are strategically placed to ensure optimal connectivity and performance and are often located in areas with high user density or where multiple network paths intersect.
An IXP is a physical location where internet service providers and CDNs connect.
An ADC is a networking device used to optimize the delivery of applications over the internet, typically as part of an application delivery network (ADN). An enterprise operating a large-scale, complex or distributed content delivery network (CDN) can also use ADCs to improve speed further and optimize performance.
CDN hosting augments web hosting (also called website hosting) by caching content in network servers that are geographically closer to website users. This differs from a web server, which hosts your entire site on the origin server. CDN hosting can, therefore, deliver content to users faster than the website's origin server.
Content delivery networks (CDNs) provide many benefits for web publishers, including:
- Better connectivity and scalability
- Reduced bandwidth consumption
- Reduced latency
- Better response to traffic spikes
- Outsourced infrastructure support
- Enhanced security
- Greater user satisfaction
- Improved content delivery
- Better search engine optimization (SEO) rankings
A content delivery network gives site users faster content load times. For web publishers that equates to more page views, traffic spikes, improved customer engagement and less site abandonment.
Web hosts charge organizations for data transferred from the origin server. By storing copies of content closer to the users, a CDN enables fewer data transfers from the origin server, reducing an organization's bandwidth consumption and costs.
Latency refers to the delay between when data is requested from a system and when it starts sending it in response. A greater distance between an end user requesting web content and the server delivering it can result in more significant latency. Because content delivery network servers store web content caches closer to your users, these servers can provide low latency and improve performance.
A successful marketing campaign, a limited-time offer, a video gone viral—these events can create a sudden (anticipated or unanticipated) increase in traffic demand. Content delivery networks use load balancing to distribute this demand across servers to prevent overloading any single server. Load balancing also helps keep the spike or surge in demand from impacting website performance.
By relying on a CDN, an organization does not have to spend time, human capital or money building out and maintaining its own geographically distributed server network.
Content delivery networks employ analytics and automation tools to uncover distributed denial of service (DDoS) attacks, man-in-the-middle (MITM) attacks and firewall issues.
Slow load-time issues with media playback and application responsiveness are among the reasons users abandon or avoid websites. Working with a content delivery network provider can prevent or reduce some of these performance issues to meet user request demand. By ensuring higher availability and lowering the risk of downtime, CDNs make it more likely that content consumers will be satisfied with their site interactions for a better overall experience.
CDNs deliver content faster and improve the quality of the delivered internet content. Slow transmissions can hinder video replay, video calls and live video streaming and might result in jitter. Buffering, poor image and sound quality and incomplete transmissions also affect the delivery of video and audio content. Content delivery networks help by shortening the distance between the content and the user and load-balancing traffic to prevent overwhelming routers or servers.
CDNs can help boost SEO rankings by improving load times, making websites faster and reducing bandwidth—all site attributes that search engines such as Google favor.
A content delivery network (CDN) primarily offers improved web content delivery, but CDN providers provide additional services that complement serving up content. According to 6sense, over 3,972,497 companies worldwide are currently using one or more content delivery network (CDN) software tools to handle web traffic.1 These tools can include:
- CDN security services
- Private CDNs
- CDN analytics
- CDN storage
CDN security is a comprehensive strategy designed to ensure end-to-end security. This holistic approach integrates artificial intelligence (AI) and machine learning (ML) tools to identify and respond to threats in real-time.
CDNs can provide DDoS protection to data centers and websites. In a distributed denial of service (DDos) attack, the attackers try to overwhelm a domain's DNS servers with more traffic than they can manage with the objective of disrupting or degrading service. CDNs use analytics and automation to monitor for these attacks and respond by limiting request rates (the number of information requests that an HTTP can make in a specified time period).
In a man-in-the-middle (MITM) attack, the attacker tries to intercept or alter the communication between the origin server, CDN servers and website visitors. MITM attacks can occur at various points in a network, but CDNs can help mitigate them by adopting Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols. This strategy helps secure communications between the CDN and the website origin server and between the CDN and the ISP.
CDNs also integrate with perimeter and web application firewalls (WAFs) to protect websites from cybercrimes like malicious bots. While standard firewalls protect at the port level, WAFs ensure requests are safe before forwarding them to web servers.
Some CDN providers offer private CDNs, which provide customers with their own dedicated network of servers and resources. A private CDN might appeal to an organization with strict security needs or specific geographic requirements, or one that simply wants its own dedicated edge servers that are highly available and won't suffer any latency issues.
Many content delivery network providers offer real-time analytics for monitoring website traffic and gathering metrics about visitors to a site. The objective is to track user behavior. With that information, website and web application creators can optimize content for users, improve site service and target marketing efforts to specific user personas.
For website operators with robust content storage needs, content delivery network providers offer storage clusters that integrate with their network of edge servers. Website operators might want this storage capability if they serve large static files, such as videos or installation files. CDN storage delivers better service and faster downloads by storing these files closer to the user. These storage options also relieve the traffic burden on the origin server by decreasing load requests and routing those requests to CDN edge servers instead.
Every content delivery network (CDN) provider maintains its own pricing structure. Most charge a monthly fee based on gigabytes of data transferred from the edge servers to users. Rates vary based on the destination (the region where cached content is hosted and accessed by users). Providers also have different storage policies, some charge storage fees while others do not.
Major CDN providers post pricing on their websites. Most providers' per-gigabyte rate decreases as the total gigabytes of data transferred increase. Leading CDN providers also charge their customers only for the bandwidth used each month so that billing reflects actual service use.
Several providers even offer free levels of service. What is included in that free level of service varies widely by provider. Free and paid levels of service come with specific service level agreements (SLAs). Leading CDN providers tend to offer 99.9% uptime to customers.
Before choosing a CDN provider, understand its pricing structure and SLAs. Since most providers charge based on actual bandwidth used, estimate usage before choosing a service to gain a general idea of monthly costs. There are CDN pricing calculators online that help you compare pricing among top providers based on bandwidth estimates and bandwidth use by geographical region.
The proliferation of content delivery network providers has been spurred by the increase in the types of content and devices used to access that content.
Top providers of CDNs and CDN-related solutions include:
- Akamai
- MaxCDN
- Incapsula
- Rackspace
- Cloudflare
- IBM
- Amazon Web Services (AWS)
When choosing a CDN provider, consider the size and distribution of its network, how well its server locations (PoPs) map to the locations of your site users, customer support availability, pricing and service level agreements (SLAs). Also, consider whether the provider offers additional services that would be helpful to your organization, such as added website security and analytics services.
Only some organizations can justify the cost of working with a content delivery network. Open-source CDNs provide a less costly option, although more time- and labor-intensive. With open source CDNs, you can link to libraries of content, such as CSS or JavaScript frameworks.
Open-source CDNs host elements of website infrastructure on CDN servers. Website content managers can access that content for free. Open-source CDNs do not host your website's original content. However, they can improve content delivery by moving common web structural elements your site uses closer to your users.
According to a report from Cisco, 72% of web traffic crosses through content delivery networks (CDNs).2 This percentage continues to grow as businesses expand their global reach and offer more varied content types. CDNs help distribute traffic loads so no single server is overloaded with network traffic requests. In another report from Future Market Insights, Inc., analysts predict a CAGR of 15.6% for the global CDN market, fueling its value to a remarkable USD 51.89 billion by 2034.3
Use cases for CDNs include the following:
Ecommerce consumers have high expectations for online shopping experiences—they expect fast product-image load times, quick payment method approvals and easy transactions on any mobile or desktop device. Content delivery networks help B2C and B2B retailers deliver high-quality ecommerce content and apps quickly during peak traffic periods.
CDNs minimize data transfer delays by caching game content on multiple servers, eliminating lag time to create optimal gaming experiences.
Social media platforms like Facebook and Instagram cater to different material for different users, and CDNs support content segmentation.
By caching content and API requests on edge servers, CDNs reduce bandwidth usage and improve the overall mobile user experience. CDNs can also quickly and securely transfer data to mobile devices, including sensitive customer data like banking information.
A CDN helps reduce latency and buffering to deliver superior live streaming and video on demand.
A content management system (CMS) is software that helps users create, manage, store and modify their digital content. A CDN can significantly enhance the speed and performance of CMSs like Adobe or WordPress by serving content from geographically distributed servers and reducing the workload on the origin server.
Avoid network traffic jams and decrease latency by keeping your data closer to your users with Akamai’s content delivery network on IBM Cloud®.
Get DDoS protection, global load balancing and a suite of security, reliability and performance capabilities.
IBM® NS1 Connect is a managed service for authoritative DNS and traffic steering that improves application performance and network resilience.
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Load balancing lets you evenly distribute network traffic to prevent failure caused by overloading a particular resource.
DDoS attacks flood websites with malicious traffic, making applications and other services unavailable to legitimate users.
Want to save time on DNS management? Using a single, fully automated DNS control plane across CDNs gives you the power to make necessary changes without the annoyance of manual configurations.
Learn how cloud at the edge brings cloud computing resources to the edge of the network—where the traffic is.
Learn more about network and network functions in relation to cloud at the edge.
Latency is a measurement of delay in a system. Network latency is the amount of time it takes for data to travel from one point to another across a network.
Footnotes
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1 Content delivery network, 6sense, 2024.
2 Cisco Annual Internet Report (2018-2022), Cisco, 2020.
3 Content Delivery Network (CDN) Market Soars with a Remarkable 20.8% CAGR, anticipated to Reach USD 155,461.3 Million by 2033 | FMI, Future Market Insights, 11 January 2024.