Content Delivery Network (CDN)

The foundational capability. CDNs cache static assets (images, CSS, JS) on edge servers close to users. Modern CDNs also intelligently cache dynamic content by following cache-control headers, using stale-while-revalidate directives to serve fast, slightly outdated content while asynchronously fetching a fresh version from the origin. This drastically reduces origin load and time-to-first-byte (TTFB).

A markup language that enables dynamic content assembly at the edge. An ESI tag in an HTML page instructs the CDN edge server to fetch and assemble a fragment from another URL before delivering the final page. This allows a page with a highly dynamic shopping cart (TTL: 0s) and a static product description (TTL: 1 day) to be composed from separately cached pieces, maximizing cache hit ratios.

Modern CDNs perform real-time content transformation on the edge. This includes:

• Image optimization: Automatically converting to next-gen formats like WebP/AVIF, resizing, and compressing images based on the client's device.
• Code minification: Stripping whitespace and comments from JavaScript, CSS, and HTML.
• HTTP/3 prioritization: Serving assets using the latest multiplexed protocol for faster loading.

A markup language that instructs an edge server to assemble a web page from multiple dynamic fragments. Each fragment can have its own cache policy (e.g., a static header cached for 24 hours, a personalized cart cached for 0 seconds). This allows the CDN to compose the final HTML at the edge, drastically reducing origin requests for pages with mixed cacheability. The W3C specification defines tags like <esi:include> and <esi:choose> for conditional logic.

A unique identifier assigned to a piece of content, enabling targeted cache invalidation across a CDN. Instead of purging an entire URL, you send a single API call with the surrogate key (e.g., product-1234), and the CDN instantly purges all cached objects—HTML pages, JSON responses, image renditions—tagged with that key. This is essential for maintaining content freshness in dynamic assembly without massive, indiscriminate cache flushes.

A server-side pattern where a final UI is assembled by aggregating rendered fragments from multiple, independent microservices or templates. Unlike client-side composition, this happens before the response is sent, often at the CDN edge or an API gateway. Each fragment team owns its rendering logic and data contract. The composition layer merges these fragments into a single coherent page, enabling independent deployability and technology diversity across teams.

A distributed computing paradigm that runs application logic on servers located at the network edge, co-located with CDN points of presence. This allows developers to execute custom code—authentication checks, A/B test bucketing, geolocation-based redirects—within milliseconds of the user, without a round-trip to a central origin server. Platforms like Cloudflare Workers and Fastly Compute@Edge enable full dynamic content assembly directly on the CDN node.

An architectural approach where multiple specialized content services and APIs are interconnected to form a unified, graph-based content layer. Rather than a monolithic CMS, a content mesh federates data from headless CMSs, PIMs, and legacy databases. The CDN acts as the delivery and assembly point, querying the mesh to resolve relationships and compose pages. This decouples content producers from presentation logic, enabling omnichannel delivery.

A hybrid rendering strategy that allows developers to update static pages on a per-page basis after a site has been built, without a full rebuild. When a request hits a CDN-cached page that has expired, the CDN serves the stale version while triggering a background regeneration. The next request gets the fresh page. This combines the speed of static site generation with the flexibility of dynamic content, ideal for large-scale content sites with frequent updates.