How CDN Technology Supercharges Web Content Delivery

What is CDN?

Content Delivery Network (CDN) is a network of computers connected via the Internet that uses servers closest to each user to deliver music, images, video, applications, and other files faster and more reliably, providing high performance, scalability, and low-cost content delivery.

CDN Name Resolution

Content

In CDN, “content” refers to HTTP resources such as HTML, images, video, application packages, etc.

Resources are classified as static or dynamic. Static resources are unchanging (e.g., images, audio) and can be cached; dynamic resources change per request (e.g., inventory, follower count) and generally cannot be cached unless Cache-Control allows short-term caching, turning them effectively into static resources.

Network

The core principle of CDN is “proximity access”. From a network transmission perspective, speed depends on four factors:

Outbound bandwidth of the website server’s link to the ISP.

Inbound bandwidth of the user’s client link to the ISP.

Bandwidth of interconnection points between different ISPs along the path.

Physical transmission latency between website and user; for gamers, latency (ping) often matters more than bandwidth.

If a user can obtain data within a few dozen kilometers, latency is essentially zero.

Distribution

Users access the nearest CDN edge node (a caching proxy) instead of the origin server, reducing long-distance travel time and achieving network acceleration.

Passive origin pull: When a user requests a resource not present in the cache, the CDN node fetches it from the origin in real time.

Active push: The origin pushes content to edge nodes using any transport method (HTTP, FTP, P2P, etc.) and any schedule.

Cache management: Common practice combines time‑based passive expiration with manual active invalidation via provider APIs, often automated by CI pipelines.

Overview

CDN (Content Delivery Network) originated in 1996 from an MIT research group to improve Internet service quality. By 1999, dedicated CDN companies emerged, serving Yahoo. Major telecoms (AT&T, Deutsche Telekom, China Telecom) built their own CDNs. Akamai became the largest pure CDN provider with over 1,000 nodes worldwide. In China, ChinaCache (formerly Blue Cloud) started in 2000 and now operates over 50 nodes across the six major backbone networks, with bandwidth exceeding 35 G and serving over 300 customers.

Functions

Key CDN functions include: (1) saving backbone bandwidth, (2) server‑side acceleration to prevent overload, (3) local caching of web pages to reduce bandwidth and improve response time, (4) mitigating uneven site distribution and lowering construction/maintenance costs, (5) reducing impact of “traffic storms” and improving stability.

Routing Resolution

CNAME

CNAME (Canonical Name) records map one domain name to another, allowing the second domain to serve the content.

After adding an accelerated domain in the CDN console, a CNAME like kunlun.com is assigned; you add this CNAME record at your DNS provider to point the accelerated domain to the CDN.

Resolution Process

When CDN is involved, DNS resolution proceeds as follows (example using www.huaweicloud.com). Using dig or host commands reveals the DNS response chain, showing CNAME records that eventually resolve to multiple A records representing CDN edge nodes across the country.

<code>~# dig www.huaweicloud.com

; <<>> DiG 9.10.6 <<>> www.huaweicloud.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 59710
;; flags: qr rd ra; QUERY: 1, ANSWER: 7, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;www.huaweicloud.com.  IN A

;; ANSWER SECTION:
www.huaweicloud.com. 29 IN CNAME www.huaweicloud.com.cdn.dnsv1.com.
www.huaweicloud.com.cdn.dnsv1.com. 29 IN CNAME cdn-koa8myv3.sched.s2.tdnsv5.com.
cdn-koa8myv3.sched.s2.tdnsv5.com. 29 IN A 110.185.117.243
cdn-koa8myv3.sched.s2.tdnsv5.com. 29 IN A 118.112.23.208
cdn-koa8myv3.sched.s2.tdnsv5.com. 29 IN A 110.185.115.189
cdn-koa8myv3.sched.s2.tdnsv5.com. 29 IN A 110.185.117.191
cdn-koa8myv3.sched.s2.tdnsv5.com. 29 IN A 182.150.11.59

;; Query time: 3 msec
;; SERVER: 223.5.5.5#53(223.5.5.5)
;; WHEN: Fri Sep 17 11:03:53 CST 2021
;; MSG SIZE  rcvd: 204</code>

The resolution shows that after registering the origin server’s IP as a source, you receive a CNAME (e.g., www.huaweicloud.com.cdn.dnsv1.com) which you add as a DNS record. When a user first accesses the site, the DNS query returns the CNAME, after which the CDN’s authoritative DNS selects the optimal edge node based on topology, capacity, latency, etc., and returns its IP. The browser then contacts that IP, which may already have the content cached, completing the accelerated delivery.

Content Storage

Origin Storage vs. Cache Node Storage

CDN systems must handle both origin storage (often several TB, high throughput) using massive storage architectures like NAS and SON, and cache node storage, which is a critical design aspect.

Cache storage must support various content formats and partial caching, especially for streaming media where users may watch only portions of a video, improving space utilization and response time, though it may introduce fragmentation.

Reliability is typically achieved with RAID configurations, though implementations vary across devices.

Content Management

Hit and Origin Pull

Two key CDN concepts:

“Hit” means the requested resource is found in the cache and returned directly.

“Origin pull” means the cache missed and must retrieve the resource from the origin server.

Metrics: hit rate (hits / total requests) and origin pull rate (origin pulls / total requests). Good CDNs achieve >90% hit rates, effectively multiplying origin capacity tenfold.

Resource Update and Invalidation

Because many developers are unfamiliar with HTTP caching, strict header‑based invalidation can be problematic. The common practice combines time‑based passive expiration with manual active invalidation via provider APIs, often automated by CI pipelines.

Additional Capabilities

Efficient Transfer Protocols

Many CDN providers offer integrated SSL certificates, allowing HTTP origins to be served over HTTPS.

They can also translate HTTP/1.x to HTTP/2 or HTTP/3 for clients, and support IPv6 even if the origin uses IPv4.

Robust Security Features

CDNs provide security measures to mitigate business risks:

Anti‑hotlinking via referer, UA, URL, IP checks or custom EdgeScript.

DNS hijack protection using HTTPDNS to bypass ISP DNS.

HTTPS encryption with TLS, supporting TLS 1.3, HSTS, keyless, etc.

Origin protection and optional SCDN for stronger security.

Conclusion

CDNs have evolved over two decades from simple static‑resource accelerators to platforms supporting Web 2.0, HTTPS, video, live streaming, SSL acceleration, content optimization (compression, image format conversion, transcoding), anti‑hotlinking, WAF, and more. Websites can focus on producing quality content while CDNs handle the “busy work”.

Geographic distance makes direct access slow, prompting CDN adoption.

CDNs build nationwide or global private networks, allowing users to access nearby edge nodes and reduce latency.

GSLB acts as the CDN “brain”, using DNS load balancing to intelligently dispatch edge nodes.

The cache system is the CDN “heart”, employing HTTP proxy caching; hits return instantly, misses trigger origin pull.