The Science of Acceleration
Most “CDN is broken” tickets are cache headers, query strings, or a missing purge. These four pages cover the HTTP side of EdgeCaching.
Why is my CDN not updating?
The object is still within TTL. Purge the URL or the zone, then hard-refresh. If query strings differ, you may be looking at another cached variant.
Should I cache HTML?
Usually no for WordPress/Magento storefronts. Cache static assets aggressively; keep HTML on origin or a short TTL.
Does purge cost money?
Purge is included. Abuse (purging the world every second) is an operational problem, not a line item on the 2013 price table.