Stripe uses MongoDB as its database, leveraging replica sets for high availability and easy replication configuration. To handle large write loads and query volumes, Stripe structures its application to use idempotent writes, retries failed operations with backoff and timeout, and avoids hot data evictions from the cache. Stripe's native events processing system, Monster, uses MongoDB as a persistent queue for event production and consumption. MongoDB's features, such as zero-downtime migrations and robustness against failures, are crucial to Stripe's uptime and availability. The Ruby driver is used in various configurations, with some desired features including forcing reads from secondaries. Currently, Stripe's engineering roadmap focuses on scaling its systems to keep up with growth while making the service available outside the US.