Enable secure offline reservation caching

Q: Enable secure offline reservation caching

This question evaluates a candidate's ability to design offline-capable web architectures, covering Progressive Web Apps, Service Workers, IndexedDB schema and metadata, synchronization and conflict-resolution strategies, and client-side encryption and privacy protections for reservation data.

Q: How do I approach System Design interview questions?

System Design questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master system design interviews.

Q: What difficulty level is this interview question?

This is a hard difficulty System Design question, commonly asked during Onsite rounds at Airbnb.

Q: What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Airbnb during technical interviews.

Question

System Design: Offline Caching for Reservations (PWA)

Design a web application that supports offline access to reservation information. The app is a progressive web app (PWA) that uses a Service Worker and IndexedDB. Assume users need to see their upcoming reservations and critical trip details when offline.

Specify the following:

Data Caching

What data to cache in IndexedDB (e.g., reservations list, details, assets). Identify which fields are necessary offline and which must never be cached.
How to structure the IndexedDB stores and metadata to support consistency and encryption.

Networking and Synchronization

How the Service Worker intercepts requests to serve cached data and update in the background (e.g., stale-while-revalidate for GETs).
Background sync for queued writes (e.g., modifications/cancellations). Define retry strategy, backoff/jitter, idempotency, and when to give up.
Versioning and cache invalidation using ETags/If-None-Match or If-Match, TTLs by data type, and cache busting on logout.
Conflict resolution after reconnect: how to detect conflicts and merge or surface them to the user.

Security and Privacy

Identify sensitive data (PII/secrets) vs. non-sensitive.
How to encrypt cached data at rest in the browser (algorithms, key hierarchy), key derivation and storage, and how keys are unsealed on login.
Token lifetimes and refresh strategy compatible with a Service Worker.
PII minimization choices: what to omit or mask.
Protections against XSS/CSRF exfiltrating cached data and secrets.

Testing and Auditing

A test plan covering offline/online transitions, sync correctness, encryption, and failure injection.
A security review and audit plan, including logging/telemetry without leaking PII.

Enable secure offline reservation caching

Quick Overview

Enable secure offline reservation caching

System Design: Offline Caching for Reservations (PWA)

Data Caching

Networking and Synchronization

Security and Privacy

Testing and Auditing

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