CDN · Content Delivery Network
Content Delivery Network
What is a CDN?
- Copies content to servers worldwide
- Delivered from the nearest location
- Faster, more reliable
The moment you add a CDN, the variable that drives performance shifts from the server spec sheet to distance and round trips. If a single origin server in Seoul serves users in the US and Europe, every request round trip simply loses 200–300 ms, and on a product page loaded with dozens of images that delay stacks up. Doubling the CPU won't shave off a single millisecond. The real change is that the fix moves from adding servers to shortening the distance to the user.
Adoption is relatively easy. Switching an image domain to a CDN address takes about half a day, and many Korean hosting and online store platforms offer it as a default option. However, results depend on what you choose to cache. Static files such as images, CSS, JS, and fonts can reach hit rates above 90%, but responses that differ per person, like login status or shopping carts, should generally not be cached. Start by measuring what percentage of requests pass straight through to the origin.
There are two controls. TTL is how long an edge server keeps a copy, and a purge is the command that deletes that copy on demand. Files that change often, such as banners, get a TTL of a few minutes, while build outputs with a hash in the filename get one year. A CDN is not a load balancer: spreading requests across several back-end servers and placing copies at the front are different layers. WAF and DDoS protection are usually priced separately, and because billing is based on transfer volume (GB), traffic is cost, so build that into your budget.
The most common mistake is assuming a CDN will speed things up on its own once it is installed. If you set a long TTL and never purge, an expired discount price stays visible for days, and customer service gets complaints that the screen showed KRW 19,000 (≈ US$14). Worse is when personalized responses get cached: miss a single line in the cookie or Vary header settings and Customer A's order history appears on Customer B's screen. Document which content is cached and which paths are excluded, and add an automatic purge to your deployment pipeline. That is the first-week job.
Seungtae ParkHands-on AX instructor who teaches AI business development and marketing automation by building real systems
John KimInstructor John Kim, CEO of Nanum Consulting and author of “B2B Marketing Design”CDNs emerged in the late 1990s (Akamai and others) to handle surging web traffic by delivering content from geographically distributed servers, and have since become standard infrastructure for web performance and reliability.
Consider a hypothetical case. Company A, a Korean cosmetics brand with 120 employees and annual revenue of about KRW 38 (≈ US$1) billion, opened its online store to the US and Singapore two years ago. A single product page carries more than 40 high-resolution images, and although overseas traffic grew, purchase conversion stayed at 0.4%. Adopting a CDN was put forward as a six-week improvement project.
- When Park, the e-commerce team lead, pulled the access logs, the first screen took an average of 8.2 seconds to load for US users, and only 3% reached the shopping cart. The meeting notes record that doubling the servers changed nothing.
- Manager Kim, who handles infrastructure, first moved only the image, CSS, and JS domains to the CDN and set the TTL to 7 days. The work took half a day, and in the first week the cache hit rate climbed to 88%.
- The marketing team complained that the banner was still showing two hours after the flash sale ended. We lowered the TTL to 5 minutes for the banner folder only and connected an automatic purge API to the deployment script.
- The login, cart, and order-history paths were explicitly excluded from caching. Manager Kim left behind a 12-item header checklist, warning that one missed line here would expose someone else's order page.
- Six weeks later, first-screen load time for US users had dropped from 8.2 seconds to 2.1 seconds, and bounce rate from 62% to 38%. Origin server traffic fell 71%, and the monthly CDN bill was KRW 840,000 (≈ US$630).