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A content delivery service usually means a content delivery network (CDN): a distributed layer of servers that delivers web pages, files, and media from locations closer to users. It works alongside your website’s origin server or storage; it can cache eligible content, but it does not automatically replace the place where that content is hosted.
What a content delivery service does
A CDN places edge servers, also called points of presence, across a network. When someone requests an image, page asset, download, or video, the CDN can respond from an edge location instead of making every request travel to the origin. Google Cloud describes this arrangement as delivery between a client, a cache, and a configured backend; Cloudflare likewise distinguishes CDN delivery from web hosting. Google Cloud: Cloud CDN overview; Cloudflare: What is a content delivery network (CDN)?
The origin remains the source of the content. It may be a web server, a storage bucket, or another backend, including infrastructure hosted on-premises or in another cloud. The CDN sits in front of that source to deliver cacheable responses and route requests; it is not, by itself, a substitute for hosting. Google Cloud: Cloud CDN overview; Google Cloud: External backends specified by using internet NEGs
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- A request reaches an edge. The CDN receives a user’s request at a network location that can serve that request.
- The edge checks its cache. The cache key and caching rules determine whether a usable copy of the requested response is present.
- A hit is served from the cache. If the response is available, the edge returns it without that request needing to fetch the response from the origin.
- A miss goes to the origin. If the edge has no usable copy, it forwards the request to the backend. If the returned response is cacheable, the edge may store it for later requests.
Google Cloud calls data transfer from the origin into a cache “cache fill” and delivery from cache to the client “cache egress.” Its Cloud CDN documentation describes objects being stored at a particular cache after a request passes through it and the response is cacheable; it does not automatically replicate every object to all other caches. That is documented behavior for Cloud CDN, not a rule that should be assumed for every CDN. Google Cloud: Cloud CDN overview; Google Cloud: Cloud CDN documentation
Why not every request is a cache hit
Whether a response can be cached depends on properties of the response, HTTP headers, and service configuration. A site’s rules may also set how long a copy remains usable. Dynamic or personalized content may need to be handled differently from a shared image or stylesheet. As a result, a CDN does not guarantee that every request avoids the origin or that every type of content is stored at an edge. Google Cloud: Cloud CDN documentation
What content CDNs commonly deliver
- Static website assets: images, JavaScript, and CSS files.
- Downloads: software packages and other large files.
- Media: streaming video, user-uploaded videos and photos, and ecommerce product imagery.
These are examples, not a limit on what a CDN can deliver. Microsoft also documents CDNs serving static assets to Microsoft 365 users. Google Cloud: Resources; AWS: How CloudFront delivers content; Microsoft Learn: Content delivery networks – Microsoft 365 Enterprise
What benefits to expect—and what a CDN cannot guarantee
Serving a cached response from an edge closer to a user can shorten the delivery path and reduce work at the origin for that request. Providers describe speed and latency improvements as intended benefits, but there is no fixed improvement that applies to every site. Results depend on where the audience is, whether requested content is cacheable, the pattern of requests, and the service’s configuration. Measure performance with the workload and regions that matter to your site rather than relying on a general promise. Google Cloud: Cloud CDN overview; Cloudflare: What is a content delivery network (CDN)?
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How to think about CDN types and choices
“CDN” describes a category of service, not one standard product or setup. For example, Google Cloud distinguishes Cloud CDN for web acceleration from Media CDN for media delivery. The right service depends on what is being delivered and how the application works. Google Cloud: Choose a CDN product; Google Cloud: Media CDN overview
If you are evaluating a service for a real application, consider these dimensions:
Quick Recap
- Workload: Is the priority static website content, downloads, dynamic application traffic, live video, or on-demand media?
- Origin compatibility: Can the CDN reach the existing backend, including a server on-premises or in another cloud? Google Cloud: External backends specified by using internet NEGs
- Cache controls: How are cache keys, cache eligibility, expiration, invalidation, and misses configured?
- Audience geography: Does the service have useful coverage where your actual users are? A provider’s stated footprint alone does not establish performance for your workload.
- Operations and terms: Check integration requirements, security features, logging, service levels, support, and pricing. These vary by provider and should be checked against current service documentation and terms.
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