A CDN is a delivery layer between users and an origin. Edge servers store or fetch content, then serve it from a nearby location when possible. A cache hit avoids a trip to the origin; a cache miss requires the edge to fetch the content or forward the request.
This article explains the general architecture. It does not claim that FAST-VID operates its own CDN or uses a specific third-party CDN unless that is separately verified.
What a CDN is
A CDN is a network of geographically distributed servers that deliver web content on behalf of an origin. The origin is the authoritative source: an application server, object store or media packager. Edge locations are the points of presence that users connect to.
CDNs can handle static files, images, software downloads, video segments, API acceleration and security functions. For media, the CDN may cache segments or complete files and stream them to viewers.
The CDN does not own the content or grant rights to it. It is infrastructure that follows cache and access rules configured by the operator and the origin.
Edge locations and caching
When a user requests a resource, DNS or anycast routing can direct the request to a nearby edge. If the edge has a fresh cached copy, it can respond directly. If not, it requests the content from the origin or another cache layer, then may store it for later requests.
Caching works best for content that is the same for many users and does not change constantly. A video segment, image or static player asset is a good candidate. A personalized playlist, account page or signed URL may need different handling.
The cache key determines which stored response can satisfy a request. URL, query string, headers, cookies and device variation can all affect whether two requests share one cache entry.
Cache hits and misses
A cache hit means the edge serves a stored copy without contacting the origin. A cache miss means it must fetch the content, which adds latency and origin load. A stale response is a cached copy that has passed its freshness lifetime but may still be served while it revalidates.
Hit ratio is not the only measure of success. A high hit ratio with stale or incorrect content is worse than a lower ratio with correct responses. Cache rules should match the content’s freshness and privacy requirements.
Conditional requests, ETags and Last-Modified values help a cache revalidate a stale object without downloading it again. The origin still has to answer correctly.
| Event | Meaning | Operational note |
|---|---|---|
| Cache hit | Edge serves a stored copy | Low origin load and lower latency |
| Cache miss | Edge fetches from origin or parent | Adds latency and origin traffic |
| Stale | Stored copy needs revalidation | Can still be served while checking |
| Purge | Explicit removal | Propagation varies across edges |
Cache behavior should be measured rather than assumed. A high hit ratio with stale content is not success, and a low hit ratio may be correct for personalized responses.
Invalidation and expiration
A cached object can expire after a time-to-live, be revalidated, or be explicitly purged. Invalidation can be necessary after an upload, a metadata change or a correction. It is not always instant across every edge, and propagation can take time.
Versioned URLs are a common alternative to purging: a new filename or query version creates a new cache key, so clients fetch the new object while old copies expire naturally. This can be easier to reason about than broad invalidation.
Stale content is not necessarily a CDN bug. It may be the intended result of a long TTL. The right balance depends on how often the content changes and how costly a stale response would be.
Why some content is not cacheable
Dynamic or personalized responses may depend on a user, session, location or request header. A CDN can still accelerate the connection, terminate TLS or route the request, but it may not cache the response body.
Signed URLs and authorization headers are often designed to prevent shared caches from serving one user’s private content to another. A CDN must be configured to respect those rules; a cache misconfiguration can create a privacy incident.
Live and real-time media may use short-lived segments and low-latency delivery rather than long-lived cache entries. The architecture is different from a static video-on-demand file.
Security and origin protection
CDNs commonly provide HTTPS termination, DDoS mitigation, WAF rules, bot controls and origin shielding. These are useful layers, but they do not automatically make an application secure. Origin access should still be restricted, credentials protected and application input validated.
HTTPS between the viewer and the edge protects that segment. The connection from the edge to the origin also needs protection and authentication. A CDN can terminate TLS and then use a separate secure connection to the origin.
Access controls, signed URLs, token expiry and geo restrictions are policy decisions. A CDN can enforce some of them, but the origin remains responsible for authorization logic.
Why CDN performance varies
Performance depends on the user’s distance to an edge, the path between edge and origin, cache hit ratio, object size, TLS handshakes, congestion and the device. A nearby edge with a cache miss may be slower than a direct origin response for a small dynamic object.
Different providers have different footprints, peering, cache rules and regional performance. A benchmark from one location or time does not generalize to every audience.
For video, segment size and bitrate also matter. A CDN can deliver segments quickly, but it cannot make an oversized file fit a slow connection or fix a player that chooses the wrong quality.
How FAST-VID relates to CDNs
FAST-VID serves pages and completed media files from its own deployment path. The current configuration includes a reverse proxy and an internal egress path for worker fetches, but this article does not assert that FAST-VID operates a CDN or uses a particular third-party CDN.
The worker’s source fetch and the browser’s file delivery are separate connections. A CDN in front of a site would affect the browser-to-site path, not automatically the worker-to-source path. Caching rules and access tokens still apply.
If you operate a media service, measure cache behavior and origin load for your own workload rather than assuming that “CDN” means a fixed performance result.
Frequently asked questions
What does a CDN do?
It delivers content from distributed edge locations, often caching copies closer to users to reduce latency and origin load.
What is a cache hit?
A cache hit means the edge serves a stored copy without contacting the origin. A miss requires a fetch or forwarding request.
Does a CDN cache every response?
No. Dynamic, personalized, authenticated or uncacheable responses may be forwarded rather than stored.
Is a CDN automatically more secure?
No. It can provide TLS, DDoS mitigation and WAF features, but origin security and correct authorization remain necessary.
Does FAST-VID use a CDN?
This article does not claim that FAST-VID operates its own CDN or uses a specific third-party CDN. That would need separate verification.
Sources and references
- Cloudflare: What is a CDN?
- Cloudflare: Cache documentation
- AWS: Amazon CloudFront overview
- MDN: HTTP caching
- FAST-VID: Streaming vs downloading
Try FAST-VID
Open the FAST-VID downloader for a supported public link. Delivery behavior depends on the source and network; no CDN performance guarantee is implied.