CDN: what Content Delivery Networks are and why to use them
It is called Content Delivery Network, or CDN, and it is literally a network for delivering multimedia content, or rather, it is an infrastructure of various servers located and extended globally that are tasked with distributing these resources over the Internet: in short, CDNs provide resources quickly, reduce the load on the originating server, and are useful for handling traffic peaks, so much so that even Google recommends their use to meet performance quality goals. So let’s try to define the CDN and discover its positive features for the SEO.
What is a CDN
Content Delivery Network, acronym CDN, means content delivery network.
It is a platform composed of several servers strategically placed in various parts of the world, designed to host and distribute copies of digital content, with the goal of reducing or zeroing out latency in data transfer and loading times of pages and online resources.
Your ally for Google success
These servers act as local access points for users, regardless of their geographical location, thus ensuring that data travels the shortest possible distance. In particular, a CDN has the function of distributing via the Internet some content of particular and heavy sites, such as image files, videos, audio, HTML files, CSS and Javascript, to decrease the physical distance between the server and the user and reduce the delay in loading such resources
CDNs can be used by any type of website, from small blogs to large companies with millions of visitors per day, and many hosting platforms offer built-in CDN options or add-ons for their services. Thanks to this system, users around the world can view the high-quality content of a site without delays in loading, with positive effects on user experience and benefits for the site as well.
The key features of CDNs
In practice, then, this network of servers distributed around the world is designed to reduce latency times and improve the speed and reliability of access to online content. In short, it functions as an intermediary between the user’s website and the originating server where the content is hosted.
Although they are probably best known for the distribution of cached content, CDNs can also improve the distribution of uncacheable content. In general, experts say the more of our site we deliver through a CDN, the better.
Without a CDN, a user from Italy accessing a site hosted in the United States might experience longer load times due to distance. The CDN intervenes precisely to minimize this delay, also known as latency, by storing a copy of the content on servers closer to the user and thus reducing the time it takes to transfer data.
When a user accesses a website that uses a CDN, in fact, the request is automatically routed to the CDN server closest to the user’s geographic location. This server caches website content, such as images, videos and web pages, and distributes them to the user over a high-speed connection. This significantly reduces content loading time and improves user experience.
No less important element, this process not only speeds up the loading of pages, but also helps to handle large traffic peaks by spreading the load across multiple servers, thus preventing overloading a single server. In addition, the CDN can also increase website security through the use of technologies such as SSL encryption and protections against DDoS attacks, and thus ensure a stable and reliable web presence.
How the Content Delivery Network works
The primary function of a CDN is to serve Web pages and other Web content, such as video or images, to users based on their geographic location, the origin of the Web page, and the CDN server itself.
To understand how a CDN works, let’s first look at the classic situation for sites that do not use this system.
The distribution of content without CDN is based on a single server, which must provide answers to every request of visitors to the site, whether they are located in the immediate geographical vicinity, or located on the other side of the world. This results in a high source traffic, which therefore generates a significant load that can make it more likely a failure of the original server, especially in situations of peak traffic or persistent load.
In contrast, the CDN consists of multiple servers that respond to requests from end users from the nearest physical and network location to their location. In this scenario, the content is stored in several places simultaneously, ensuring a wider geographical coverage that reduces the distance for data transfer and, in this way, lowers waiting times for users.
Understanding CDNs
In a digital age characterized by the attention economy, every millisecond counts: whether it’s loading a page, streaming a video, or ensuring the security of transactions, speed and efficiency in online content delivery have become crucial aspects for any web business with ambitions for success.
And so, Content Delivery Networks become key allies for anyone who wants to ensure fast, reliable and secure web performance because they help deliver an optimal online experience. From large e-commerce companies to small blogs that want to reach a global audience, using it can make the difference between a satisfied user and a frustrated one.
For instance, again, without a CDN if a UK user wants to view the contents of a web page hosted on a server in the US, the loading times will be long because the request has to cross the entire Atlantic Ocean. Through the use of a CDN, however, the answer to the user will come from the server closest to its location, with significant time savings and no negative effects on quality.
A CDN network acts essentially as a multi-route traffic intersection to which different providers and Internet servers can connect and provide each other with access to website traffic from each source. A CDN transmits resources and traffic back and forth as resources are called from page loads, instead of waiting for each resource to be loaded onto individual pages or rendering as a hard-coded element. In addition, this process happens worldwide in multiple locations, unlike the “old system” to rely on a single server for all services and delivery of content; to further reduce the loading time and delivery path, These server hosts keep files cached ready for rendering when they are called.
In addition, because the CDN servers are distributed equally among different geographical regions, the load on the original website server is also reduced.
How Content Delivery Networks are made: the architecture of CDNs
The architecture of a Content Delivery Network is a sophisticated technological component designed to maximize efficiency in the distribution of digital content.
To simplify, the CDN is classically composed of an origin web server, which is called the Content Provider or Origin Server, and the set of Edge Servers, also called Content Servers or Delivery Servers, which are the servers on which content is replicated. This structure can also reach extensive sizes of a few thousand nodes, spread over tens of thousands of servers and located in various geographic locations, often near major Internet exchange points to reduce latency.
Each server stores or caches copies of a subset of Web content (HTML files, images, audio, video, applications) from the host server in multiple geographic areas of the world, known as Pop (Point of Presence). Each Pop has its own caching servers, which concretely allow you to distribute the required content according to the user’s location.
These servers are interconnected and work in a coordinated way to handle user requests. When a user tries to access content, such as a Web page or video, the request is initially sent to the nearest CDN server. If the content is already present on that server, it is immediately delivered to the user. If the content is not present, the CDN retrieves the data from the originating server, stores it for future requests, and then delivers it to the user.
CDNs therefore also use caching techniques, which consist of temporarily storing copies of the most requested content, to reduce the number of times the data must travel from the origin server to the end users. This not only speeds up content loading but also reduces the load on the central servers and the bandwidth used.
The heart of this process is the Request Routing, which directs requests to Edge Servers and also establishes how the contents are replicated, and then sent, to users.
CDNs are capable of serving a very wide range of content, including high-quality images and videos, audio streams, software downloads (apps, games and OS updates), data records containing medical and financial information, and “potentially any digitized piece of data can be distributed via a CDN” (Akamai).
The process of content distribution and resource delivery
To use a CDN, Web site owners must upload their content to the system network and configure settings on their Web site to point to the network; there are many companies that offer paid or free CDN services, with various options and features available. And so, ultimately, site owners can turn to a CDN service provider (such as Akamai, a world leader in the field) for the ability to distribute website content to each server on the network.
These servers store cache versions of the site’s content, making it immediately available for user requests. When a user requests a page, in fact, the content is delivered via the server geographically closest to him, identifying copies of web content closer or facilitating the delivery of dynamic content (as in the case of live video feeds).
Although it might seem illogical, using a CDN to distribute resources, even those that cannot be cached, is generally faster than downloading the same resource directly from the source servers.
Using a CDN to transfer resources starts with the establishment of a new connection between the client and a CDN server in the immediate vicinity. The next segment of the path, that is, the transfer of data from the CDN server to the origin, takes place within the CDN’s own network. This network usually maintains already active and persistent connections with the origin server. The advantages are significant: concluding the new connection as close to the user as possible eliminates the unnecessary costs associated with setting up the connection, which is an onerous and time-consuming process. In addition, using an already active and “hot” connection allows data to be transferred immediately and at the maximum allowable speed.
Some CDNs further optimize the data transfer process by routing traffic to the originating server through a series of CDN servers located throughout the Internet. These internal CDN connections make use of stable and optimized routes, unlike those that would be determined by the Border Gateway Protocol (BGP), the Internet’s fundamental routing protocol. Although BGP manages the directions of traffic on the Internet, it does not always guarantee maximum performance efficiency. As a result, routes chosen by BGP may be less efficient than those optimized within the CDN’s network.
How to activate a Content Delivery Network or CDN service
Activating a CDN service is not difficult, and it all starts with choosing a reliable and professional CDN provider who will provide us with registration and account creation. Typically, the provider will also provide an intuitive user interface for managing functionality.
The next step is to integrate the CDN to our website, and this can be done through several ways: for example, by using a dedicated CMS (Content Management System) plugin or by manually adding the necessary codes to the web pages-at a high level, the configuration process consists of registering with a CDN provider, then updating the DNS CNAME record so that it points to the CDN provider.
Once the site integration is complete, we need to configure caching and static file management options, which serves to optimize content distribution on the network and improve the user experience.
Finally, it is important to carefully test the CDN to ensure that it is properly configured and working properly; if there are any problems or difficulties, the provider should provide dedicated technical support to help users resolve any issues.
Ideally, it is suggested that a CDN be used to serve the entire site. If using a CDN to serve all resources is not an option, it is still possible to configure a network to serve only a subset of resources, such as only static resources.
The advantages of a CDN for both site owners and users
In short, Content Delivery Networks are a network of servers optimized to rapidly deliver content to users, and essentially reduce server load, reduce server costs, and are well suited to handle peak traffic.
In summary, the performance advantages of CDNs stem from a number of principles: CDN servers are located closer to users than origin servers and thus have shorter round-trip latency (RTT); network optimizations enable CDNs to deliver content faster than when content was loaded “directly” from the origin server; and finally, CDN caches eliminate the need for a request to reach the origin server.
Thanks to Content Delivery Networks, the physical distance between the content and the users is minimized and, therefore, the latency is reduced, which represents the delay between the forwarding of a request on a web page and the completion of the loading of the same on the device in use.
But Cdns also improve loading speed and user experience, because they optimize delivery based on the type of content required – standard web content, dynamic content, video streaming or downloading large files – and also increase bandwidth and reduce overhead costs for servers.
No less important is the security aspect: content distribution networks use analytics and automation tools that can detect DDoS attacks (Distributed Denial of Service), man-in-the-middle attacks, firewall problems and others, and so increase the security of the server, data and applications in use.
Ultimately, then, Content Network Delivery helps the publisher of a site to provide faster performance, reduce loading times for its users, control bandwidth consumption, avoid or fix overloaded server problems and reduce costs, both traffic and economic.
CNDs and performance: key features
Going into more detail, there are a number of performance features that CDNs commonly offer as part of their basic service package-and it is paradoxical to note that many sites do not take full advantage of these features, thus missing out on the opportunity to greatly improve performance.
- Compression
Compression of text-based responses is critical and should be done using gzip or Brotli. If given the choice, Brotli is the preferred option. This more modern compression algorithm outperforms gzip, achieving higher levels of compression.
There are two main modes through which CDNs support Brotli compression: “Brotli from the source” and “automatic Brotli compression.” In the first case, “Brotli from origin” (Brotli from origin) a CDN distributes resources already compressed with Brotli directly from the origin server; this feature requires the ability to handle multiple versions of the same resource, i.e., those compressed with both gzip and Brotli, for a single URL. In the case of automatic Brotli compression, on the other hand, it is the CDN itself that compresses the resources, both those that can be cached and those that cannot be cached. When a resource is first requested, it is provided with a “good enough” level of compression, such as Brotli-5, applicable to both types of resources. In the case of cached storable resources, the CDN then proceeds with offline processing to further compress the content to a higher level, such as Brotli-11, which is more effective but also slower. The more compressed version is then cached for future requests.
In general, to maximize performance, sites should implement Brotli compression on both the origin server and the CDN; compression at the origin minimizes the size of resources that cannot be served by the cache.
- HTTP/2 and HTTP/3
HTTP/2 and HTTP/3 are both superior to HTTP/1 in terms of performance. Of the two, HTTP/3 promises the greatest performance advantages, even though it is not yet fully standardized.
- Image optimization
Image optimization services offered by CDNs focus on automatic interventions to reduce the size of images during transfer. These include removing EXIF data, applying lossless compression, and converting images to more efficient formats, such as WebP. Considering that images account for about 50 percent of the data transferred in an average web page, optimizing them can have a significant impact on reducing the overall page size.
- Minimization
Minimization consists of removing unnecessary characters from JavaScript, CSS and HTML. It is preferable to perform this operation on the origin server, where site owners have a more thorough knowledge of the code and can therefore adopt more incisive minimization techniques than on a CDN. However, if minimization at the origin is not possible, that performed by the CDN remains a viable alternative
Why to choose a Content Delivery Network
The average Web user “does not care about how web pages work or the web hosting provider used by a company, and all that interests them is their user experience, intended primarily as upload speed, quality content and intuitive navigation“, comments Kevin Rowe on Search Engine Journal.
Speed means money, and this is especially true for e-commerce sites, and various studies show that pages that load within 0-2 seconds have the highest e-commerce conversion rates. In addition, conversion rates decrease by an average of 4.42% with each additional second of loading time between 0 and 5 seconds.
Even for non e-commerce sites, page load rates determine profits, because they can affect the bounce rate: sites that load in 1 second have an average bounce rate of 7%, while pages with a 3-second page latency have a bounce rate of 11% and those that take 5 seconds rise to 38% of rebound.
In all sectors, then, the use of CDN is a standard strategy to achieve optimal page loading speeds for both desktop and mobile devices: a Cisco research shows that global CDN networks are expected to transport 72% of all Internet traffic by 2022, and it is “almost impossible now to meet user expectations and compete with competing sites without using CDNs”.
This is especially true in view of the now coming Page Experience Update, which will make ranking factors the Core Web Vitals (and other technical parameters related to the user experience on the page) and therefore requires to verify the performance of the site on elements such as loading, interactivity and visual stability. And Google has expressly recommended the use of CDN for SEO, both for image optimization and for the improvement of the LCP, the largest contentful paint that is one of the essential web signals examined by the search engine.
Statistics on the deployment of Content Delivery Networks
As Web Almanac 2022 (the latest one published so far) reveals, CDNs now play an increasingly important role in delivering content to users around the world, even for smaller sites, facilitating the distribution of static and third-party content such as JavaScript libraries, fonts and other content.
Awareness of their benefits is steadily increasing and so is their use: classically CDNs are used to deliver static content such as images, style sheets, JavaScript and fonts, types of content that do not change frequently and are therefore good candidates for caching on CDN proxy servers. A more recent trend, also a result of this increased attention and widespread use of the system, is the increase in basic HTML pages served by CDNs, a technique that can improve the page load time itself.
And so, looking at CDN use for websites based on their popularity through data from Google’s Chrome UX report, we note that the vast majority of sites in the top 1,000 to 10,000 exploit precisely this technology. As the report explains, it is understandable that companies that own top-tier sites are investing in CDNs for performance and other benefits. It is interesting, however, that even among sites falling in the top 1 million there has been an increase of about 7 percent in the amount of content delivered via CDN compared to the previous year, a trend that can be attributed to the fact that there has been an increase in free and affordable CDN options and many hosting solutions have CDNs bundled with services.
How to choose a CDN: characteristics to evaluate
In the early days, a CDN was a simple network of proxy servers that performed three essential functions:
- Cache content (such as HTML, images, style sheets, JavaScript, video, and so on).
- Reduce network steps to allow end users to access content.
- Offload TCP connection termination away from data centers hosting web properties.
In other words, they mainly served to improve page load times and offload traffic from the infrastructure hosting these web properties.
Over time, however, the services offered by CDN providers have evolved beyond caching and bandwidth/connection offloading. By virtue of their distributed nature and large distributed network capacity, CDNs have proven extremely efficient in handling large-scale distributed denial-of-service (DDoS) attacks, just as edge computing has gained popularity, allowing applications to run and data to be managed directly on servers at the edge of the network. And so, CDN providers today also provide additional services such as.
- Web application firewalls (WAFs) hosted on the cloud.
- Bot management solutions.
- Clean pipe solutions (Scrubbing Data-center).
- Image and video management solutions.
The process of choosing a Content Delivery Network provider has thus become more complicated because the variables to consider have increased. It is true that performance is often a key factor in choosing a CDN, but precisely we should not overlook the other features it can offer, such as security and analytics options, as well as considerations such as cost, support and the onboarding process.
Specifically, expert Kate Hempenius suggests that we pay attention to these features:
- Performance
At a general level, the performance strategy of a CDN can be seen as a balance between reducing latency and increasing the cache hit rate. CDNs with numerous points of presence (PoPs) may provide lower latency due to geographic proximity to users, but this may result in a lower cache hit rate due to the distribution of traffic across multiple caches. On the other hand, CDNs with fewer PoPs may be farther away from users but are able to offer higher cache hit rates.
To manage this trade-off, some CDNs take a tiered approach to cache storage: edge caches, close to users, are supported by central PoPs with higher cache hit rates. If an edge cache does not find a resource, the search moves to a central PoP. This method may result in slightly higher latency, but it increases the probability that the resource is available in a CDN cache, even if not directly in an edge cache.
The balance between reducing latency and increasing the cache hit rate varies with needs. There is no universally best approach; it depends on the specificity of the site and its audience. Importantly, the performance of a CDN can change considerably depending on geographic region, time of day, and current events. Although it is essential to inquire about a CDN’s performance, it can be complicated to anticipate the exact performance that will be achieved.
- Effects on the LCP
As mentioned, the main goal of a CDN is to decrease latency by distributing resources through servers that are geographically closer to users, thereby improving upload performance. In particular, the Time to First Byte (TTFB) of a resource can be greatly reduced by integrating a CDN into the website server architecture.
Although TTFB is not a metric focused on user experience, it is critical in diagnosing problems related to Largest Contentful Paint (LCP), which is instead a user-oriented metric and part of the Core Web Vitals.
CDNs are particularly effective in improving LCP because they optimize both document delivery, reducing TTFB in connection configuration and document caching, and the delivery of static resources needed to render the LCP element.
- Additional features
In addition to the core features, CDNs often offer a wide range of additional services. Commonly available features include load balancing, image optimization, video streaming, edge computing, and security solutions.
What to ask of a CDN
A text by Rachel Vandernick accompanies us to the crucial features to look for in a CDN solution.
The most important aspect is obviously speed: the CDN network must be faster than our current origin, otherwise there would be no benefit in the change. In addition, we need to make sure that it works well in providing small files and large payloads in the same way.
Among the main common metrics that we can test and explore in a demonstration test of the network there are:
- DNS response time to the last mile and end user. Useful to avoid that the implementation of a complex DNS configuration can create long waits for end users.
- Performance during peak hours. If our site undergoes large traffic fluctuations based on the days of the week or the hours of the day, it is advisable to test the CDN response at the most appropriate time.
- Connection time. It is used to check if there are basic requirements such as network connectivity, low latency and zero packet loss.
- Waiting time on less popular resources. CDNs are a shared environment and it is important to know if the least requested resources are recovered from the source server compared to those served by the edge (such as popular resources).
- Cache Hit / Miss. It is not a good sign to notice many requests that return to the origin.
- Effective Range. The throughput value should not be lower than the origin for assets of any size.
- API integrations. It is good to choose a CDN that, even in the future, can be configured with the existing software or that we will develop.
More specifically, in choosing an efficient CDN provider we need to assess whether it has a wide and diverse network and know the location of its servers, to check whether it meets the needs of our target audience, both current and potential new markets.
Wanting to elaborate quickly, to choose a CDN that can meet the goals of improving site performance we must also:
- Consider the location of visitors. If most of the site’s traffic comes from Europe, we should choose a CDN with servers in Europe to reduce page load times; as you can easily guess, if the visitors are primarily located in Asian countries, it would be more appropriate to opt for a CDN with servers in Asia.
- Evaluate the features offered by the CDN provider, making sure that it supports the type of files we intend to distribute, such as images, videos or Web applications, and that it also offers caching and resource compression options, which can further reduce page load times.
- Consider cost. Many providers offer pricing plans tailored to specific needs, and obviously the price must be evaluated and measured against the benefits we expect to gain from using the CDN.
CDN costs: how much do Content Delivery Networks cost
At this point it is more than fair to ask how much does a CDN network cost? According to U.S. reports, medium-sized business sites can expect to pay around $200 or more per month for a solution based on their needs, while usually solutions for larger size businesses are almost always customized and tailored.
Generally speaking, however, the price of the service depends on several factors, such as the amount of web traffic, the geographic location of visitors, and the level of functionality required, and average rates range from a few hundred to thousands per month.
However, there are several options for choosing a CDN that suits one’s needs: some companies offer standard packages, which include a certain number of GB of monthly traffic and a certain number of server locations, while other providers offer customized rates based on the customer’s specific needs. Still, other providers provide additional services such as web security, performance optimization, and traffic analytics, which can obviously increase monthly CDN costs, but at the same time provide important benefits to improve the user experience.
Finally, it is important to consider that CDN costs may vary over time depending on the evolution of web traffic and the needs of the website, so it is useful to carefully evaluate the available options and choose a flexible and scalable solution that can adapt to the needs of the business and the site in the long run.
Who are the leading CDN providers
Thus, the CDN market continues to evolve as new players enter and existing companies expand their service offerings. Wanting to provide a quick overview, there are at least five major providers to know and evaluate:
- Cloudflare. It is one of the most popular CDN providers, with a large and reliable global network, to which it adds the offering of integrated security services, such as DDoS protection and Web Application Firewall (WAF). Their CDN service is designed to be easy to use and is integrated with a suite of performance optimization tools, such as automatic compression and image optimization. Cloudflare also stands out for its commitment to innovation, with solutions such as edge computing that allow code to run closer to the end user. One potential downside lies in the complexity of management, as it requires an average skill level to properly configure the network.
- Akamai. Akamai is one of the pioneers in the CDN industry and offers one of the most extensive and reliable networks in the world. Their focus is on speed and security, providing advanced solutions for content delivery, defense against cyber attacks, and performance analysis. Akamai is often chosen by large companies and organizations that require an enterprise-grade service with the ability to handle large volumes of traffic.
- Amazon CloudFront. Part of the Amazon Web Services (AWS) ecosystem, CloudFront integrates seamlessly with other AWS services, such as S3 for storage and Lambda for serverless processing. It offers fast and secure content delivery, with the ability to customize caching behavior and use AWS’s global network to reach users wherever they are.
- Google Cloud CDN. This is Google’s CDN, based on the Google Cloud Platform and integrated well with other services, such as Cloud Storage and Compute Engine. Claimed features include universal support for any origin and backend; security insights through Cloud Armor; granular control over cache keys, TTL and other caching features based on the origin depending on the type of content delivered; routing matching and origin selection
- Microsoft Azure CDN.Azure CDN, part of the Microsoft Azure offering, leverages Microsoft’s global network to provide a CDN service integrated with other group cloud services. It offers caching customization, performance optimization and security features such as DDoS protection. It is a suitable solution for companies that already use Azure infrastructure and want a CDN solution that easily integrates with their existing services.
CDN and SEO, why the use of a network is important
It is clear from what has been written that the choice of a CDN network is becoming increasingly urgent and unavoidable for sites with high demand traffic or requiring a global presence, and more generally is an absolute priority for SEO professionals and entrepreneurs who want to ensure an effective loading speed for the pages of their projects.
Today more than ever the UX and SEO are intrinsically intertwined, but it’s actually long since Google considered the UX elements to determine the search rankings; the current advantage is that Google has already clarified exactly what metrics it will monitor and, so which ones we need to improve.
In addition to the benefits already described, premium CDN providers also include analysis reports and insights as part of the package: CDN networks can, in fact, collect and report critical information such as audience analysis, Query-based geographic traffic data, service quality data, security event analysis, and viewer diagnostics, all useful indicators to study to improve site performance.
As said, then, the use of a CDN network also affects the security of the site, because it protects sites from denial-of-service attacks (Ddos): by distributing content to numerous servers, the network prevents Ddos attacks from hitting the original server, and even if a server within the network is attacked or receives more traffic than it can handle, the request will be redirected to another server. These security aspects can have indirect positive effects on SEO, because they improve the user experience and create trust in the site or brand.
The potential pitfalls of a CDN for the SEO
Given these advantages for SEO, however, the use of a CDN network can also lead to potential disadvantages for a site, as highlighted in Rowe’s article.
Manage all SEO aspects
First, “well-known figures in the SEO industry have questioned the impact of using CDNs on image rankings“, especially in the case of hosting images on a CDN domain or a subdomain of the website. However, “the best thing you can do to take advantage of image SEO is to still set up your CDN with a custom subdomain related to your main domain”.
Another suggestion is to “set a record or CNAME alias to clear the CDN subdomain name” and to recover link equity “by contacting sites that use your images but connect to the image source (the CDN) or image itself instead of your site” and asking their editors to edit the URL.
Another pitfall concerns duplicate content, but you just need to set up the CDN network properly to have no problems and, in particular, setting a canonical header that communicates to Google crawlers that the content on the CDN is a copy of the original.
Finally, there is a relevant aspect to consider that relates to the technical side: if we use a CDN that is configured to be aggressive in handling bots, Googlebot will not be able to pass and crawl, and therefore nothing on our site will be indexed. In other words, if our Content Delivery Network is set up to block or restrict bots excessively, this may also prevent Googlebot, Google’s crawler, from accessing the site: as a result, pages on the site will not be indexed, which means they will not be visible in search results.
