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How would you design resumable multi-step onboarding state management?
This tests cross-device onboarding resume. A strong answer uses debounced server sync for cross-device resume with localStorage fallback, covers anonymous users, and handles conflicts. Red flag: pure client or server storage ignoring offline gaps or privacy.
Design a role-based personalized onboarding system
Tests separation of content and logic for scalable personalization. Strong answer: CMS-backed rule engine, multi-channel delivery, event-driven triggers, and per-segment metrics. Red flag: hardcoding role-specific UI components in the client.
Long-term onboarding holdback: technical and data integrity challenges
This tests the engineering cost of year-long holdbacks in growth. A strong answer covers feature-flag entropy, pipeline drift, survivorship bias, and counterfactual validity. Red flag: treating the holdback as static config that never rots.
Describe the end-to-end data flow for tracking a 'Share' button click
Payload carries event type, user ID, timestamp, device, content; client batches with retry; backend validates and lands in a partitioned store.
Describe the data model and backend logic for a daily login bonus.
This tests streak state machines and calendar edge cases. A strong answer stores last_login_utc and streak_count, uses UTC day buckets, resolves timezones per user tz, and needs no leap-year logic.
Design an A/B test for a Buy Now button
This tests experiment plumbing: deterministic bucketing, sticky storage, and logging. A strong answer covers user-ID hashing, cookie persistence, and impression-plus-conversion events.
Outline architecture for a weekly email digest of unread notifications
This tests batch processing and scheduled delivery at scale. Pre-aggregate unread counts, shard digest jobs across a distributed scheduler, and cache unsubscribes for fast filtering. Never scan the notifications table at send time for millions of users.
Compare fan-out-on-write vs fan-out-on-read for an activity feed
Tests whether you tie feed architecture to read/write ratios and follower distribution. Strong answers contrast push O(1) reads with celebrity storms against pull O(1) writes with read amplification, then propose a hybrid threshold.
Design a real-time personalized notification trigger system
Stream events to a delayed queue, expose a rule UI to non-technical users, and deliver idempotently.
What schema changes are needed to add a Pro subscription tier?
This tests normalization of billing data versus hardcoding tiers. Add a plans table with integer cents pricing, link subscriptions via plan_id, and leave users untouched. Red flag: adding a tier string column to users or storing prices in subscriptions.
Model a 3-month 20% promo discount and apply it at billing
This tests separating coupon rules from per-user redemptions. Good answers use a coupons table for the 20%/3-month rule, a redemptions table for usage, and apply the discount to the first three invoices. A red flag is hard-coding the discount on the user row.
How do you ensure consistent A/B test variants across sessions and devices?
Tests stable identity and delayed attribution. Fix: one stable user ID for SDK bucketing, persisted across devices via login or first-party cookies, attached to every conversion event. Never use per-device randomization or third-party cookies.
Design a system to handle subscription renewals
States include active, past_due, and cancelled; transitions are payment success, dunning exhaustion, and grace expiry; use idempotent webhooks.
How would you instrument an application to calculate Customer Lifetime Value?
Tests whether you tie revenue and cost events to persistent identity and model cohort retention. Outline: track purchases, CAC, and churn with persistent IDs; project value via retention curves.
What are the key architectural differences between freemium and free trial models?
Contrast tiered entitlements against trial timers and revocation; discuss free-user overhead and conversion tracking.
Design a highly available entitlements service with caching
This tests balancing read performance with consistency in access control. A strong answer proposes tiered caching with proactive invalidation, read-optimized hot paths, and event-sourced temporary grants.
How would you design international monetization with multi-currency and tax?
Localized pricing, jurisdictional tax, gateway routing, async reconciliation.
How would you instrument a key activation milestone event?
Tests schema design beyond a bare event name. A strong answer includes the event key, user ID, timestamp, and properties like project_id and is_first_project. Red flag: omitting the user ID or sending only a human-readable label without structured context.
Implement a 10% onboarding tutorial feature flag and track success
Tests lightweight experiment design and metric selection beyond vanity numbers. Strong answers cover user-ID bucketing, conversion tracking, and guardrail metrics like drop-off. Red flag: manual toggles or click-through without downstream outcomes.
Design referral tracking from invite to conversion
Tests data modeling for multi-stage conversion tracking. Strong answers separate codes from conversion events, model status transitions, and enforce unique constraints. Weak answers merge invite and reward into one table or store denormalized counts on users.