SELE
Car Rental Platform in USA
A rental app that allows agencies to list cars for rent and users to rent them with real-time booking and payment. Includes in-app messaging between agencies and renters.
What was the measurable impact?
Handled multiple concurrent rentals with instant booking confirmation
What problem did SELE solve?
Rental agencies needed a modern system to manage car bookings, and customers required instant confirmation and communication for rentals.
How was SELE solved?
Developed a platform supporting agency car listings, real-time booking, payment processing, and secure messaging between agencies and customers.
How is SELE architected?
State-Driven Inventory Booking Engine with Redis TTL Locks
Prevents vehicle inventory conflict during checkout while maintaining instant confirmation and reliable booking state transitions.
- Redis atomic SETNX keys for temporary car reservation during payment checkout
- Stripe PaymentIntents integration with automated fallback release on checkout timeout
- Socket.io bidirectional messaging for real-time agency-renter negotiation
What was hard to build in SELE?
Challenge 1
Double-booking risks for popular rental cars during peak demand hours.
How it was solved
Designed a 15-minute temporary inventory lock pattern via Redis TTL keys. If checkout completes, state locks permanently; if abandoned, lock auto-expires and inventory immediately recirculates.
Challenge 2
Disconnected chat state during network switches on mobile clients.
How it was solved
Implemented persistent message queue fallback with Redis streams and automated Firebase Cloud Messaging (FCM) push notifications when socket connection drops.
What can SELE do?
- Real-time car booking
- Payment integration (one-time payments via Stripe)
- In-app messaging between agency and user
- Car listing management for agencies
- Booking notifications and status updates
- Secure account management and authentication