What is a global CDN? How does it work and what are its features?
PublishedViews3EditorJinDun TeamEstimated reading time 7 min
Your website users may be from New York, London, Sydney, or Shanghai, São Paulo, Cape Town. When they click on your page late at night, every second of waiting can be the limit of patience. If the image loads in a circle and the video lags and buffers, they are likely to turn off the page and turn to the competitor.
That's why the concept of "global CDN" is getting hotter and hotter. It's not a simple "content delivery network," but a truly global, intelligently scheduled, ubiquitous acceleration network. Today, we will thoroughly talk about what a global CDN is, how it works, and what features you can't do without.
Many people think that CDNs are all about "putting content on servers in different places." This understanding is correct, but it is too superficial.
Global CDN (Global Content Delivery Network) refers to the deployment of a large number of edge nodes around the world to direct user requests to the optimal nodes through an intelligent scheduling system, thereby achieving fast, stable, and secure content delivery services.
Global CDNs have several essential differences compared to regional CDNs:
Coverage Breadth:
Not only Beijing, Shanghai, Guangzhou and Shenzhen, but also nodes on five continents, hundreds of countries, and thousands of cities. The people who can really get the Antarctic research station also get low latency (of course, there may not be a node there, but the concept is so).
Network Depth:
Establish direct interconnection with mainstream operators (Telecom, China Unicom, Mobile, Comcast, Deutsche Telekom, etc.) to avoid cross-network congestion.
Scheduling Intelligence:
Not only "nearby", but also consider node load, real-time network quality, and cost strategy to dynamically adjust.
In other words, instead of simply placing servers around the world, a global CDN builds an intelligent, self-optimizing global data highway.
The best way to understand a global CDN is to follow a user request through it.
Let's say your web server is in Frankfurt and a user visits your website in Buenos Aires. Without a CDN, requests would travel across the Atlantic, back and forth for at least a few hundred milliseconds. With a global CDN, the process has completely changed:
The user enters www.example.com in Argentina. The browser first needs to know which server the domain name corresponds to.
The request first arrives at the local DNS server and then recursively queries upwards. Eventually, the query request is directed to your authoritative DNS server (or the smart DNS provided by the CDN). This smart DNS will not only return a fixed IP, it will make an instant decision:
So, Smart DNS returns the IP address of the São Paulo node.
The browser makes a request to the São Paulo node. The São Paulo node is the "edge node" of the CDN - the repository closest to the user.
If the São Paulo node has cached your website's homepage HTML and images, it will be returned directly to the user, and the whole process may take less than 30 milliseconds.
If the São Paulo node does not cache this content (for example, the first time someone visits from South America), it will make a request to your Frankfurt origin site on behalf of the user, and once the content is obtained:
Next, the CSS, JS, and images in this user request page will be obtained directly from the São Paulo node, because they have just been cached. Users feel that "one point opens" and have no idea that there are so many stories happening behind it.
Cache:
Pre-store your static content (images, CSS, JS, and even HTML) on global nodes.
Smart Scheduling:
Real-time monitoring of global network conditions, node load, and user location, and dynamically allocating the optimal nodes.
This is how a global CDN basically works. But the actual product is far more complex than that, such as dynamic acceleration (optimizing routing for content that cannot be cached), protocol optimization (TCP acceleration, QUIC), edge computing (executing code on nodes) and other advanced functions.
Now that we understand how it works, let's take stock of some of the top features of a global CDN and see what exactly it can bring to your website.
This is the core value of global CDNs. Without a CDN, a German user may have a delay of 150ms to visit a US website and 300ms to a Chinese website. With a global CDN, this number can be reduced to less than 50ms.
Top CDN service providers deploy thousands of nodes around the world, covering more than 100 countries. Whether you're on the South American plateau or the Pacific islands, you'll get a near-local experience.
For multinational enterprises, cross-border e-commerce, and overseas game companies, this is just a need. Your competitors may have achieved "global seconds", and you also make overseas users wait for three seconds, and this is how the gap widens.
Have you ever experienced "the website suddenly won't open"? It may be hot news, or it may be the start of a promotional event, and the traffic overwhelms the server in an instant.
Global CDNs are inherently resilient. Thousands of nodes share the traffic, and each node handles only a small portion of the request. Even if one node is overloaded, intelligent scheduling will direct new requests to other nodes.
What's more, CDNs absorb most of the attack traffic. No matter how ferocious DDoS attacks are, they are also hit on thousands of nodes and are dispersed and diluted. The origin server is as stable as Mount Tai.
Traditionally, CDNs can only accelerate static content. But modern global CDNs have evolved dynamic acceleration capabilities.
For content that cannot be cached, such as shopping carts, user logins, and API queries, CDNs can still make them run fast through intelligent routing, TCP optimization, protocol acceleration, etc. For example, Sudun CDN establishes a dedicated channel between nodes around the world to avoid public Internet congestion and make dynamic requests more than 30% faster.
Global CDNs are not only accelerators, but also the first line of defense.
DDoS protection:
Large-scale attacks are distributed across the network and are automatically cleaned.
WAF (Web Application Firewall):
SQL injection and XSS attacks are blocked at the edge layer, and malicious requests cannot reach the origin server.
Bot Management:
Identify and block malicious crawlers and ticket swiping scripts.
CC Attack Protection:
Resist application-layer attacks through frequency limiting, verification codes, etc.
For websites that lack a professional security team, this is equivalent to prostituting an enterprise-level security system for nothing.
This is the hottest direction in recent years. The nodes of global CDNs are not only "warehouses", but can also become "micro data centers".
You can deploy some business logic to edge nodes. For example:
These tasks, which would have been processed back to the central server, are now completed closest to the user with almost zero latency.
