Content Delivery Network (CDN)

The foundational mechanism of a CDN. Static assets—such as HTML files, images, CSS, and JavaScript—are stored on proxy servers at the network's edge. When a user requests a resource, the CDN serves it from the geographically nearest Point of Presence (PoP) rather than the origin server.

• Cache Hit Ratio: A critical performance metric measuring the percentage of requests served directly from cache.
• Time-to-Live (TTL): Defines how long an object remains fresh in cache before the CDN revalidates with the origin.
• Cache Purging: The ability to instantly invalidate cached content globally, essential for updating time-sensitive information.

An intermediate caching layer that sits between the edge servers and the origin infrastructure. Instead of every edge PoP requesting the same uncached object from the origin, a single shield node makes the request, caches the result, and distributes it to all edge servers.

• Origin Offload: Reduces requests hitting the origin server by up to 99%, protecting it from traffic spikes.
• Consolidated Requests: Prevents a thundering herd problem where thousands of edge servers simultaneously request the same expired object.

The network addressing technique that makes CDN geography transparent. A single IP address is announced from multiple locations simultaneously. The Internet's Border Gateway Protocol (BGP) automatically routes the user's request to the nearest available PoP based on network topology, not just physical distance.

• Latency-Based Routing: Directs traffic to the PoP with the lowest round-trip time.
• Failover: If a PoP becomes unavailable, BGP automatically withdraws its route, redirecting traffic to the next closest node without manual intervention.

Optimization techniques for non-cacheable, personalized content. Unlike static assets, dynamic requests must reach the origin, but the CDN accelerates the transit. This is achieved through route optimization, persistent connections, and protocol enhancements.

• TCP Pre-Pooling: Maintains warm, pre-established connections to the origin to eliminate the three-way handshake overhead.
• Route Optimization: Uses real-time internet telemetry to bypass congested peering points and find the fastest path to the origin.
• Protocol Upgrades: Terminates HTTP/1.1 at the edge and upgrades the origin connection to multiplexed HTTP/2 or HTTP/3.

A runtime environment distributed across the CDN's edge nodes that allows developers to execute custom logic at the point of presence. This moves computation from a centralized cloud region to the network's edge, enabling sub-millisecond cold starts.

• Request Modification: Rewrite headers, URLs, and cookies before the request reaches the origin.
• A/B Testing at the Edge: Execute traffic splitting logic without adding latency to the user.
• Authentication: Validate JSON Web Tokens (JWTs) at the edge, blocking unauthorized requests before they consume origin resources.

Real-time media transformation performed at the edge, eliminating the need for pre-generated variants. A single high-resolution source image can be dynamically resized, cropped, and converted to modern formats based on the requesting device's capabilities.

• Format Negotiation: Automatically serves WebP or AVIF to supporting browsers while falling back to JPEG for legacy clients.
• Responsive Images: Generates exact dimensions on-the-fly via URL parameters, reducing bytes transferred.
• Quality Compression: Applies perceptually lossless compression to reduce file size without visible degradation.