Scaling Magento checkout for Black Friday traffic

Checkout is the one page on a Magento store where the incentives are brutally aligned: it's the highest-value traffic you'll get all year, and it's also the page most likely to fall over under it. Black Friday doesn't create new bugs — it just finds every scaling assumption you never tested.

Full-page cache is a trap here. Checkout is inherently personalized — cart contents, shipping estimates, applied promotions — so you can't cache the page itself, but you can still cache aggressively around it: catalog fragments, shipping method lookups, tax tables. The goal is to keep the truly dynamic surface area as small as possible so your database isn't doing full price recalculations for every single page view during peak load.

Order processing is where I've seen the most Black Friday outages, and the fix is almost always the same: stop doing it synchronously. Accept the order, write it to a queue, and let workers process payment capture, inventory decrement, and notification emails asynchronously. Consumers need to be idempotent — retries during a traffic spike are not optional, they're guaranteed.

The database traps are quieter but just as damaging: lock contention on the stock and inventory tables when everyone's buying the same doorbuster item, connection pools sized for average traffic instead of peak, read replicas that exist but that nothing actually queries. Every one of these is invisible until the one day a year it matters most.

Load testing has to mimic checkout traffic specifically — logged-in carts, real promotions applied, real shipping calculations — not just hammering the homepage. A store that survives a homepage load test can still go down in the one place that actually costs you money.