Stores break on the busy day, for dull reasons

A store that is fine all week and dies on the campaign day is not suffering from traffic. It is suffering from something that was always expensive and rarely called at the same moment by two hundred people.

Usually it is a table without the index it needs, a session store on disk, or a shipping calculation that talks to an external service with no timeout. All three are invisible at ten orders a day.

Before the busy day, do the dull rehearsal: load-test the checkout, not the homepage. The homepage is cached. The checkout is where the money is and where the work happens.