Less is more. Fewer elements on the web page, fewer data queries to the database, fewer web requests, fewer system dependencies
Short critical path. Fewer hops among services or merge into one service
Async. Use message queues to handle high TPS
Isolation. Isolate static and dynamic contents, isolate processes and databases for rare items
Overselling is bad. When and how to manage the inventory is important
User experience is important. We don’t want to inform users that they have successfully placed orders but later tell them no items are available