A company runs an internal expense-reporting application that is used heavily for a few hours at the end of each month but sees almost no traffic for the remaining three weeks. The application uses a MySQL-compatible relational database. Currently they pay for a provisioned Amazon Aurora instance running 24/7, and finance has flagged the database as a major source of wasted spend. The team wants to minimize cost while keeping full relational capabilities and automatically matching capacity to the unpredictable monthly spikes. Which approach is the MOST cost-effective?