CDN is short for Content Delivery Network. It copies a website's static content to nodes distributed across multiple locations, allowing visitors to retrieve data from a nearby node and thereby reducing waiting time.
What problem does it solve?
Servers are usually located in one place. The farther away the distance, the more links data transmission passes through, and the longer the waiting time required to open a page. When visitors are distributed across different regions, a single server can hardly give everyone the same speed.
CDN's approach is to deploy nodes in multiple locations. When a user requests content, the system allocates a nearby node to respond. After the first request, the content remains on that node for a period of time, and subsequent nearby visits can retrieve it directly from there without returning to the origin server every time.
Changes brought about in several aspects
- Faster access: data comes from a closer location, so pages display faster.
- Reduced origin pressure: most repeated requests are handled by nodes, and the origin server only needs to handle origin pulls and dynamic requests.
- Improved availability: nodes are independent of one another, and a failure of an individual node will not make the whole service unavailable.
- Reduced bandwidth costs: after nodes share traffic, the origin server's bandwidth usage decreases accordingly.
- Some security benefits: common security protection capabilities can usually be enabled together, and the origin server address is no longer directly exposed.
When is it worth using?
For websites with widely distributed visitors, pages containing many images or videos, or obvious traffic peaks, the improvements from CDN are usually more noticeable. Conversely, if visitors are concentrated in the same region and the website is very small, the improvement is relatively limited, and costs need to be weighed.
Points to note during configuration
- Cache policy: which content can be cached long-term and which must return to the origin every time need to be set separately by content type.
- Content updates: after a page is updated, confirm whether the cache is invalidated in time; otherwise visitors may still see old content.
- Address configuration: access is usually integrated by adjusting DNS records. The integration method will affect existing configurations, so record them before making changes.
- Effect verification: after launch, actually test page opening speeds in different regions, and use data to judge whether expectations are met.
One-sentence understanding
CDN does not change website content; it simply places content closer to visitors. It solves the speed problem caused by "distance," not the problem of whether the page itself is bloated.