CheckinPulse: Offline-First Event Check-In PWA

Attendee check-in processes at live tech events require absolute real-time speed and reliability. Standard web apps break immediately when the venue's Wi-Fi drops or gets congested due to high client density.

If a connection is lost, check-in operations stall, leading to long queues. Any data written only on the client can easily be overwritten or lost if the browser tab is refreshed or closed.

I developed CheckinPulse, an offline-first PWA implementing client-side IndexedDB databases coupled with local transaction queues:

• Offline Local Store: Used IndexedDB for persistent browser-based storage, allowing check-ins to be recorded locally instantly even when offline.
• Sync Workers: Built synchronization service workers that monitor connection state (network online/offline events) and stream queued check-ins to backend AWS SAM lambda layers when connectivity is restored.
• Conflict Resolution: Implemented conflict resolution policies (such as server timestamp precedence) to merge duplicate event state updates seamlessly.

Under intermittent network flapping, check-in sync actions would double-submit or conflict, causing databases to register duplicate check-ins.

I resolved this by wrapping each check-in in a unique cryptographically signed transaction token on the client.

The AWS SAM sync workers use these tokens for idempotency checks, discarding any already-processed tokens at the API Gateway level to ensure absolute record integrity.