The Problem: Pushing Instant Notifications to Millions of Devices Answer-first: Uber's RAMEN system maintains persistent gRPC bidirectional streams to every active driver app. When a match is made, the ride offer travels from the matching engine to the driver's phone in under 100ms — without pol...
Source: [Dev.to](https://dev.to/vesviet/system-design-uber-ramen-how-ride-hailing-apps-push-real-time-notifications-to-millions-of-2156)