WooCommerce storefronts die on sale day because product images and category HTML share PHP workers with checkout. Cache the aisle. Never cache the cart.
What is safe to cache
Theme assets, product galleries, category pages and anonymous product HTML are shareable. They are also the majority of requests during a campaign.
Cloud CDN should serve those from 210+ PoPs. Origin Shield should collapse image misses so PHP-FPM is not a thumbnail server.
What must bypass
cart, checkout, my-account, add-to-cart query strings and anything that prints a cart fragment for a specific shopper. If those land in cache, you will show the wrong count or an empty basket.
Validate with a real test order on the Aptranet hostname before DNS cutover.
Stock and price changes
If availability must be instant, purge the product URL when stock changes, or keep a short HTML TTL on product pages and a long TTL on images.
Images rarely need to expire when a price changes. HTML does.
Full-page cache at origin still helps
A WordPress page cache and Cloud CDN stack. The origin cache reduces PHP; the CDN repeats the result worldwide.
Purge both on catalogue updates if both store HTML.