Yahoo invests a lot of resources into making sure that each of its properties is available around the clock. To assist in that task, a centralized, black-box service was created as part of dev tools to help everyone from senior management to service engineers monitor and understand the health of properties.
On the backend, the service consists of the data store, a metrics collector, aggregation tools, and the configuration store (database-driven.) On the front end, there's dashboarding, custom reports, and a self-service configuration tool.