WordPress And The CDN Origin Pull Pattern

CDN origin pull is how most CDNs serve content: the CDN fetches content from your origin when needed, caches it at edge locations, serves the cache to subsequent visitors.

Understanding the pattern helps configure CDNs effectively.

How origin pull works

Visitor requests content from CDN edge.

If edge has cached version, serves it immediately.

If edge doesn't have cached version, requests from origin.

Origin responds with content.

Edge stores in cache and serves to visitor.

Subsequent visitors in the same region get the cached version.

The cache duration

How long the edge keeps cached content. Controlled by HTTP cache headers from origin.

Cache-Control: max-age=3600 means cache for one hour.

Longer cache means less origin load but staler content. Shorter cache means more origin load but fresher content.

The cache invalidation

When content changes, the edge cache needs to invalidate. Methods:

Time-based: the cache expires; the next request triggers a fresh fetch.

Purge requests: explicit invalidation via CDN API. Plugins or custom code triggers purges when content changes.

The purge method requires integration between WordPress and the CDN. Quality caching plugins handle this.

The origin protection

Behind a CDN, the origin sees less traffic. The CDN absorbs much of the load.

For DDoS protection, CDN sits in front of attacks. Legitimate traffic gets served from cache; malicious traffic gets filtered.

The geographic distribution

CDN edges around the world serve visitors locally. Visitors in Asia get content from Asian edges; European visitors from European edges.

The latency reduction is real. Same content served from a distant origin is slower than from a nearby edge.

The honest framing

CDN origin pull is the standard for WordPress sites. Understanding the pattern helps configure caching and invalidation correctly.

For sites using CDNs without thinking about how they work, occasional issues (stale content, unexpected cache misses) get attributed to mysterious causes. Understanding the pattern makes diagnosis straightforward.