What a CDN Actually Does — Edge Nodes, Caching, and Why Tokyo Is Slow
Understand how content delivery networks distribute your site globally, how caching works, and why cache invalidation is one of the hardest problems in computing.
Your site loads in 200 milliseconds in New York. Your client in Tokyo reports it takes four seconds. You check your code — nothing wrong. You check your database — queries are fast. You check your server — it is running fine in Virginia.
The problem is not your code. The problem is physics.
Light travels through fiber optic cables at roughly two-thirds the speed of light in a vacuum. A round trip from Tokyo to Virginia and back is about 25,000 kilometers of cable. At best, that is 80 milliseconds just for the speed of light — before the server even starts processing the request. Add in multiple round trips for DNS, TLS handshakes, and HTTP requests, and you are easily looking at seconds of latency.
A Content Delivery Network (CDN) solves this by putting copies of your content on se
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