Cache product reads and static assets, but keep inventory and payment correctness in controlled write paths. Partition high-volume order or event data based on query and retention patterns. Protect flash-sale endpoints with admission control, queues, and fair rate limits so a surge does not overwhelm every dependency.

Secure customer data, restrict administrative actions, tokenize payment data through compliant providers, and avoid storing sensitive card data unless the organization has the necessary compliance program. Audit price changes, refunds, inventory adjustments, and privileged access.

Monitor checkout conversion alongside technical SLIs. A service can return HTTP 200 while a business flow fails later. Track payment success, reservation expiry, order confirmation delay, outbox lag, reconciliation mismatches, and inventory anomalies.