{"id":45195,"date":"2022-11-30T14:49:46","date_gmt":"2022-11-30T14:49:46","guid":{"rendered":"https:\/\/www.arimetrics.com\/glosario-digital\/cdn"},"modified":"2026-10-01T07:35:29","modified_gmt":"2026-10-01T07:35:29","slug":"cdn","status":"publish","type":"encyclopedia","link":"https:\/\/www.arimetrics.com\/en\/digital-glossary\/cdn","title":{"rendered":"CDN"},"content":{"rendered":"<p><img decoding=\"async\" class=\"boxpad alignright wp-image-45301 size-full\" src=\"https:\/\/www.arimetrics.com\/wp-content\/uploads\/2023\/01\/cdn.jpg\" alt=\"CDN\" width=\"300\" height=\"300\" srcset=\"https:\/\/www.arimetrics.com\/wp-content\/uploads\/2023\/01\/cdn.jpg 300w, https:\/\/www.arimetrics.com\/wp-content\/uploads\/2023\/01\/cdn-150x150.jpg 150w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><strong>Definition:<\/strong><\/p>\n<p>A <strong>CDN<\/strong>, short for Content Delivery Network, is a distributed infrastructure of servers that delivers web resources from points of presence that are close to the user in network terms. It sits between the client and the origin server to shorten routes, reuse stored responses, and manage traffic.<\/p>\n<p>A CDN can keep copies of static files such as images, stylesheets, JavaScript, video, or downloads, and act as a proxy for requests that must reach the origin. Its performance depends on the <strong>network route<\/strong>, cache configuration, content availability, and the provider&#8217;s capacity.<\/p>\n\n<h2>How a CDN works<\/h2>\n<p>The domain is configured so that selected requests reach the provider&#8217;s network, usually through the <a href=\"https:\/\/www.arimetrics.com\/en\/digital-glossary\/dns\">DNS<\/a>. The CDN selects a point of presence, or PoP, according to its topology and routing rules. This is not always the physically closest node, but the one that can provide an <strong>efficient route<\/strong>.<\/p>\n<p>The usual request flow has four stages:<\/p>\n<ol>\n<li><strong>Reception:<\/strong> The edge node receives the HTTP or HTTPS request and applies the domain&#8217;s configuration.<\/li>\n<li><strong>Lookup:<\/strong> The cache key determines whether a valid response exists for that combination of URL, headers, and parameters.<\/li>\n<li><strong>Delivery:<\/strong> On a cache hit, the node returns the stored copy without requesting the resource from the origin again.<\/li>\n<li><strong>Retrieval:<\/strong> On a cache miss, the CDN contacts the origin, returns the response, and may store it if the rules allow.<\/li>\n<\/ol>\n<p>The origin server continues to hold the reference version and process requests that cannot be cached. It may run on a <a href=\"https:\/\/www.arimetrics.com\/en\/digital-glossary\/hosting\">hosting<\/a> service, object storage, or a <a href=\"https:\/\/www.arimetrics.com\/en\/digital-glossary\/cloud-computing\">cloud computing<\/a> platform. A CDN does not necessarily replace that infrastructure; it adds a <strong>delivery layer<\/strong>.<\/p>\n<h2>Cache management<\/h2>\n<p>The <a href=\"https:\/\/www.arimetrics.com\/en\/digital-glossary\/cache\">cache<\/a> determines which responses can be reused and for how long. HTTP headers such as Cache-Control, provider policies, and the cache key contribute to the decision. A rule that is too broad may serve incorrect data, while one that is too restrictive lowers the <strong>hit ratio<\/strong>.<\/p>\n<p>Configuration commonly accounts for these elements:<\/p>\n<ul>\n<li><strong>Static content:<\/strong> Images, fonts, CSS, JavaScript, and downloadable files are usually good candidates for caching.<\/li>\n<li><strong>Dynamic content:<\/strong> Pages generated on request may pass through the network without being stored or use specific rules by fragment, route, or response.<\/li>\n<li><strong>Private content:<\/strong> Sessions, accounts, shopping carts, and personalised responses require exclusions or keys that prevent information from being shared between users.<\/li>\n<li><strong>Expiration:<\/strong> The TTL limits how long a copy remains valid; invalidation or versioning can remove resources before they expire.<\/li>\n<li><strong>Variants:<\/strong> Parameters, cookies, device, language, and headers may form part of the key, although too many combinations fragment the cache.<\/li>\n<\/ul>\n<p>Using HTTPS requires the network to manage certificates and encrypted connections, in relation to protocols such as <a href=\"https:\/\/www.arimetrics.com\/en\/digital-glossary\/ssl\">SSL<\/a> and TLS. Encryption protects data in transit, but it does not correct permissions, vulnerable applications, or unsuitable cache decisions. Security requires a <strong>consistent configuration<\/strong> at the edge and origin.<\/p>\n<h2>Benefits of a CDN<\/h2>\n<p>The main effect appears when a response can be served from the edge or travel through an optimised network. The actual improvement varies by region, content type, hit ratio, and origin status. Within a <a href=\"https:\/\/www.arimetrics.com\/en\/digital-glossary\/wpo\">WPO<\/a> strategy, a CDN is a <strong>complementary measure<\/strong>, not an isolated guarantee of speed or rankings.<\/p>\n<p>Its operational benefits include the following:<\/p>\n<ul>\n<li><strong>Lower latency:<\/strong> It shortens part of the route and avoids repeatedly retrieving the same resources from a distant origin.<\/li>\n<li><strong>Lower origin load:<\/strong> Cache hits reduce requests, data transfer, and processing on the origin infrastructure.<\/li>\n<li><strong>More capacity:<\/strong> Traffic distribution helps absorb peaks without concentrating every connection on a single server.<\/li>\n<li><strong>Greater continuity:<\/strong> Some services can switch between origins or keep resources available during partial incidents.<\/li>\n<li><strong>Edge services:<\/strong> Depending on the provider and plan, WAF, DDoS mitigation, bot controls, compression, or image transformation may be added.<\/li>\n<\/ul>\n<p>These functions are not available to the same extent on every network. A basic CDN may focus on distributing and storing content, whereas an edge platform integrates more controls. The <strong>available protection<\/strong> should be distinguished from the essential delivery function.<\/p>\n<h2>Operational control<\/h2>\n<p>A poorly configured CDN can retain an outdated version, cache private responses, or create unnecessary variants. It can also temporarily conceal an origin problem without solving it. Monitoring therefore covers the <strong>cache hit ratio<\/strong>, status codes, latency by region, origin traffic, and edge errors.<\/p>\n<p>Provider dependency introduces costs for requests and transfer, invalidation limits, configuration changes, and possible differences between regions. Access logs and stored copies may also create <strong>privacy and location<\/strong> requirements for data. These considerations are part of the architecture, not only performance.<\/p>\n<p>The origin also needs protection. If it remains accessible without controls, an attacker may bypass the edge network and contact it directly. Restricting access where appropriate, retaining recovery capacity, and documenting rules allow the CDN to work as a <strong>controlled layer<\/strong> rather than a single point of dependency.<\/p>\n<h2>Current CDN services<\/h2>\n<p>The market includes specialist networks and services integrated into cloud platforms. Their <strong>service models<\/strong> differ in coverage, cache configuration, edge computing, security, observability, and billing. Current providers and products include the following:<\/p>\n<ul>\n<li><strong>Akamai:<\/strong> A distributed network focused on delivery, security, and edge services.<\/li>\n<li><strong>Cloudflare:<\/strong> A network platform with CDN, reverse proxy, DNS, and security functions.<\/li>\n<li><strong>Fastly:<\/strong> A programmable CDN and edge platform with detailed cache and delivery control.<\/li>\n<li><strong>Amazon CloudFront:<\/strong> An AWS service connected to HTTP origins and other resources on the platform.<\/li>\n<li><strong>Google Cloud CDN:<\/strong> A Google Cloud service that delivers content through its edge network and compatible load balancers.<\/li>\n<li><strong>Azure Front Door:<\/strong> A global Microsoft service for application delivery, acceleration, and edge functions.<\/li>\n<\/ul>\n<p>The choice depends on audience location, origins, volume, content types, and required controls. Comparison should use project-specific measurements and technical requirements because the number of points of presence alone does not demonstrate <strong>better delivery<\/strong> for every project.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Definition: A CDN, short for Content Delivery Network, is a distributed infrastructure of servers that delivers web resources from points of presence that are close to the user in network terms. It sits between the client and the origin server to shorten routes, reuse stored responses, and manage traffic. A CDN can keep copies of [&hellip;]<\/p>\n","protected":false},"author":6,"featured_media":0,"template":"","encyclopedia-tag":[1267,1268],"class_list":["post-45195","encyclopedia","type-encyclopedia","status-publish","hentry","encyclopedia-tag-web-infrastructure","encyclopedia-tag-web-performance"],"_links":{"self":[{"href":"https:\/\/www.arimetrics.com\/en\/wp-json\/wp\/v2\/encyclopedia\/45195","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.arimetrics.com\/en\/wp-json\/wp\/v2\/encyclopedia"}],"about":[{"href":"https:\/\/www.arimetrics.com\/en\/wp-json\/wp\/v2\/types\/encyclopedia"}],"author":[{"embeddable":true,"href":"https:\/\/www.arimetrics.com\/en\/wp-json\/wp\/v2\/users\/6"}],"wp:attachment":[{"href":"https:\/\/www.arimetrics.com\/en\/wp-json\/wp\/v2\/media?parent=45195"}],"wp:term":[{"taxonomy":"encyclopedia-tag","embeddable":true,"href":"https:\/\/www.arimetrics.com\/en\/wp-json\/wp\/v2\/encyclopedia-tag?post=45195"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}