Two Distribution Models
A CDN can fill its caches in two ways. The choice shapes how fresh content arrives and how much you manage manually.
Pull CDN
The edge fetches content from origin on the first request, then caches it.
- No upfront upload since content is lazy loaded on demand
- The first user in a region pays a miss penalty
- Great for large libraries where only some assets are popular
Push CDN
You upload content to the CDN ahead of time, and it distributes copies.
- No cold miss because the file is already placed
- You manage what to push and when to expire
- Good for large files or predictable launches like a software release
Choosing
Pull suits most websites with changing, long tail content. Push suits a small set of heavy, frequently downloaded assets where you cannot afford a first request miss.
Key idea
A pull CDN lazily caches content on first request while a push CDN pre places it; pull fits changing long tail assets and push fits heavy predictable files.