This topic covers the end to end practice of clarifying ambiguous problem statements, eliciting and defining functional and non functional requirements, and scoping solutions before design and implementation. Candidates should demonstrate the ability to identify target users and user journeys, conduct stakeholder interviews, ask targeted and probing clarifying questions, surface hidden assumptions and root causes, and convert vague business language into measurable technical and business requirements. They should capture acceptance criteria and success metrics, define key performance indicators, and translate requirements into testable statements and test strategies that map unit, integration, and system tests to requirement risk and priority. The topic includes assessing technical constraints and operational context such as expected scale, throughput and latency requirements, data volume and read write ratios, consistency expectations, real time versus batch processing trade offs, geographic distribution, uptime and availability expectations, security and compliance obligations, and existing system state or migration considerations. It also requires evaluation of non technical constraints including timelines, team capacity, budget, regulatory and operational concerns, and stakeholder priorities. Candidates are expected to synthesize inputs into clear artifacts such as product requirement documents, user stories, prioritized backlogs, acceptance criteria, and concise requirement checklists to guide architecture, estimation, and implementation. Emphasis is placed on scoping and prioritization techniques, distinguishing must have from nice to have features, conducting trade off analysis, proposing incremental or phased approaches, identifying risks and mitigations, and aligning cross functional teams on scope and success measures. Expectations vary by seniority: entry level candidates should reliably ask core clarifying questions and avoid solving the wrong problem, while senior and staff candidates should rapidly prioritize requirements, anticipate critical non functional needs, align solutions to business impact, and communicate trade offs and timelines to stakeholders.
MediumTechnical
69 practiced
Draft a stakeholder interview script focused on security and compliance for a healthcare app (HIPAA). Include 10 core questions you would ask legal, security, operations, and product owners to capture constraints that affect technical design.
Sample Answer
Purpose: Rapid stakeholder interview script to surface security/compliance constraints (HIPAA) that will drive technical design decisions. Use ~30–45 minute session; record answers and follow up for artifacts (policies, risk assessments, BAAs).Introduction (30s): Explain goal — identify legal/security/ops/product constraints that affect architecture, data flows, encryption, logging, and incident response.Core questions (ask to Legal, Security, Ops, Product owners; note stakeholder in brackets):1. What PHI types will the app collect, store, or transmit? Which fields are sensitive or subject to special handling? (Product / Legal)2. What permitted uses and minimum necessary rules apply to this data? Any role-based access restrictions? (Legal / Product)3. Are there existing Business Associate Agreements (BAAs) or vendor requirements we must enforce? Any required contract clauses or audit rights? (Legal / Ops)4. What encryption standards are required in transit and at rest (algorithms, key management, HSMs)? Who owns keys? (Security / Ops)5. What authentication & authorization models are acceptable (MFA, SSO, identity proofing, IAM providers)? Any SAML/OAuth constraints? (Security / Product)6. Retention and deletion: required retention periods, archival, right-to-be-forgotten processes, and secure deletion proof? (Legal / Ops)7. Logging, monitoring, and audit: what events must be logged, retention, access to logs, and tamper-evidence expectations? (Security / Ops)8. Incident response and breach notification: timelines, notification recipients, forensic requirements, regulatory reporting thresholds? (Legal / Security)9. Deployment & environment constraints: allowed cloud regions, on-prem vs cloud, network isolation, VPC/segmentation, and change-control requirements? (Ops / Security)10. Third-party integrations: what due diligence, scanning, penetration testing, and security certifications (SOC2, HITRUST) are required for vendors/APIs? (Legal / Security / Product)Follow-ups: Ask for policy documents, prior risk assessments, acceptable risk thresholds, and examples of past incidents. Clarify who has final sign-off for compliance acceptance.
HardBehavioral
58 practiced
Behavioral: Tell me about a time when you discovered the team was building the wrong solution because of ambiguous requirements. What action did you take to re-scope, how did you communicate with stakeholders, and what was the outcome? Use STAR format and highlight measurable impact.
Sample Answer
Situation: On a payments feature at my last company, engineering had built six sprints of integration work based on a high-level PRD. During an end-to-end test, I discovered the flow didn’t match merchant needs: the team had assumed synchronous settlement, but the business required eventual consistency with retry semantics. That mismatch would have caused failed transactions for ~15% of users.Task: As the senior engineer on the project, I needed to stop further work, re-scope requirements accurately, and align engineering, product, and ops so we could ship a correct, timely solution.Action:- I paused new feature merges and created a short spike to reproduce the merchant scenario and quantify failure modes (2 days).- Convened a rapid 1-hour triage with the Product Manager, QA lead, and Ops to present findings, failure rates, and risk.- Drafted an updated RFC specifying async settlement, idempotency, retry policy, and acceptance criteria; included sequence diagrams and test cases.- Led two backlog grooming sessions to break work into a prioritized roadmap: critical reliability changes first, UX fallback next, optimizations last.- Established daily 15-minute sync for the sprint and demoed a runnable prototype to stakeholders within 5 days for sign-off.Result: By stopping and re-scoping, we avoided shipping a broken flow. The revised plan added one sprint but reduced likely customer-facing failures from an estimated 15% to <1%. Rework (rollback/fix cycles) dropped by 60% compared to similar past releases, and merchant support tickets in the first month were zero for that flow. Stakeholders praised the data-driven, collaborative approach; product adopted the RFC template for future features.Learning: Early validation spikes and concrete acceptance criteria prevent costly assumptions; tight, transparent stakeholder communication makes brief delays acceptable when they avert larger failures.
HardSystem Design
74 practiced
Create a requirement checklist for scaling a messaging system across multiple regions that covers latency targets, durability guarantees, replication strategy, capacity, cost, and compliance. Provide concise trade-offs and a recommended high-level architecture for each major decision.
Sample Answer
Requirements checklist for scaling a global messaging system (covering latency, durability, replication, capacity, cost, compliance), with trade-offs and recommended high-level architecture per decision:Requirements & Targets- Latency: P99 end-to-end ≤ 50ms within region, ≤ 200ms cross-region (configurable per tenant).- Durability: Messages at-least-once by default; exactly-once optional for premium flows.- Replication RPO/RTO: RPO ≤ 5s, RTO ≤ 30s for regional outage.- Throughput / Capacity: baseline 50k msg/s per region with headroom x3; per-tenant quotas.- Cost: target $/million messages within business SLA; tiered storage (hot/warm/cold).- Compliance: data residency by region, encryption at-rest/in-transit, audit logs, retention policies, GDPR/CCPA/HIPAA flags.Design decisions, trade-offs, recommended architecture1) Replication strategy- Options: synchronous cross-region vs async multi-master vs active-passive.- Trade-off: sync = strong consistency/latency penalty; async = lower latency, potential duplication.- Recommend: asynchronous regional primary + configurable cross-region replication (CDC/event log) with causal metadata; for customers needing strong consistency, offer sync-writes within geo-fenced clusters.2) Durability & delivery semantics- Options: write-ahead log + ack model; retention tiers.- Trade-off: synchronous fsync per write (durable) vs buffered (better throughput).- Recommend: commit to local durable log (fsync configurable) -> replicate to remote before ack for stronger durability; support at-least-once by default, idempotent consumer pattern and optional dedupe tokens for exactly-once.3) Latency & routing- Choices: client-to-nearest-region routing, edge gateways, global load balancer.- Trade-off: affinity reduces latency but complicates cross-region ordering.- Recommend: region-aware DNS + global edge proxies; local writes served locally; if cross-region ordering required, route through a global sequencer service (optional).4) Capacity & scaling- Approach: partitioned topics, autoscaling brokers, sharded metadata (consistent hashing).- Trade-off: more partitions -> parallelism but ordering cost.- Recommend: partition-by-key with configurable partition count per topic, autoscale broker pool, quota enforcement per tenant.5) Cost controls- Techniques: tiered storage (hot: SSD, warm: HDD, cold: object store), retention policies, compaction.- Trade-off: cold storage lowers cost but increases read latency.- Recommend: TTL + lifecycle policies moving older segments to object storage; offer retention tiers to customers.6) Compliance & security- Requirements: regional data residency, KMS per region, encryption, WORM/immutable logs, audit trails.- Trade-off: strict residency increases replication complexity and cost.- Recommend: policy-based routing to store customer data only in allowed regions; per-tenant encryption keys; centralized audit stream (masked where required).High-level architecture (text diagram)Clients → Edge Gateway (region) → API Layer / Auth → Local Broker Cluster (partitioned log, durable local WAL) → Replication Service (async to other regions / global store) → Storage: hot local segments + cold object store → Consumer groups via regional brokers → Monitoring/Alerting/AuditOperational considerations- Observability: per-topic P99, replication lag, consumer lag, error budget.- SLOs & throttling: circuit-breakers, backpressure, tenant throttles.- Disaster recovery: cross-region failover runbooks, automated leader election, periodic DR drills.This checklist maps requirements to concrete design choices; adjust sync/async replication, durability fsync, and cross-region routing per tenant SLAs to balance latency, cost, and compliance.
EasyTechnical
68 practiced
When designing an external REST API, what clarifying questions should you ask about authentication, rate limits, versioning, payload size, and SLA expectations before writing the API contract? List at least 12 questions and explain why each matters.
Sample Answer
1) What authentication schemes do you require (API key, OAuth2, mTLS, JWT)? — Determines token lifecycle, libraries, and client implementation complexity. 2) Who issues and rotates credentials? — Impacts onboarding, automation, and key-rotation policies for security compliance. 3) What scopes/roles and least-privilege model are needed? — Drives authorization design, endpoint granularity, and access checks. 4) How long should tokens live and is refresh supported? — Affects session management, refresh endpoints, and security vs UX trade-offs. 5) What rate limits per client, user, and IP are acceptable (requests/sec, burst, monthly)? — Informs throttling strategy, quota storage, and fair-use enforcement. 6) How should we communicate rate-limit headers and error responses? — Ensures clients can back off gracefully and implement retries. 7) Are there different SLAs for tiers (free, paid, partner)? — Determines prioritized routing, throttling exceptions, and monitoring/alerts. 8) What are uptime, latency, and error-rate targets? — Drives capacity planning, SLOs/SLA, and monitoring/incident playbooks. 9) What maximum payload sizes for requests/responses and supported content-types? — Impacts validation, streaming vs buffering, and proxy/load‑balancer config. 10) Should we support pagination, filtering, and partial responses? — Affects payload size control, performance, and client efficiency. 11) How will versioning be handled (URL, header, semantic)? — Prevents breaking changes, migration planning, and compatibility guarantees. 12) What deprecation policy and notice period do you expect? — Sets communication cadence, tooling to manage versions, and rollout timeline. 13) Are there compliance, logging, or audit requirements (PII, retention)? — Affects data storage, redaction, and access controls. 14) What client SDKs, protocols (HTTP/2), or CORS requirements exist? — Guides implementation choices and developer experience.These questions clarify security, reliability, performance, backward compatibility, and operational responsibilities before drafting the API contract.
MediumSystem Design
74 practiced
A legacy monolith handles orders. Product asks to extract the payments module into a microservice. From a requirements and scoping perspective, list the technical constraints, migration risks, data consistency considerations, and an incremental rollout strategy you would propose.
Sample Answer
Requirements & constraints- Functional: authorize, capture, refund, void, store payment methods (PCI scope), retry logic, idempotency, audit trail, reconciliation, KPIs (latency, throughput).- Non-functional: PCI-DSS compliance, throughput (~orders/sec), SLOs (p99 latency), high availability, observability, deployability.- Integration: support current payment providers, backwards-compatible API for order service, retry/backoff, secure secrets, rate limits.Technical constraints & design decisions- Keep payments data separated; service owns payment state; orders reference payment_id.- Use synchronous call for authorization (low latency path) and async events for reconciliation and refunds.- Persistence: strong consistency for payment state (ACID DB) and append-only ledger for audit (immutable events).- Network: circuit breaker, bulkhead, rate-limiting.Migration risks- Downtime or partial failures causing lost payments or double-charges.- Inconsistent semantics between monolith and new service (idempotency mismatch).- Increased latency on happy path.- PCI scope mistakes exposing sensitive data.- Operational complexity: monitoring, runbooks.Data consistency considerations- Use event-driven pattern: monolith writes an "initiate_payment" event while new service becomes the source of truth for payments.- Two-phase pattern for safe cutover: orchestrated syncs + reconciliation job to compare ledgers.- Idempotency tokens and monotonic transaction IDs to prevent double processing.- Compensating transactions for failures (refunds/voids).- Reconciliation: daily/real-time diffs between order and payment stores, alerting, manual correction flows.Incremental rollout strategy1. Build service behind feature flag; run in shadow mode: mirror requests to new service and compare responses without affecting live flows.2. Select low-risk traffic: route subset of customers/orders to new service (canary) with full monitoring.3. Switch read-after-write: new payments created in service; orders still read legacy data for verification until parity confirmed.4. Dual-write for transitional period: monolith writes to both payment DB and service via API; reconciliation validates parity.5. Full cutover: route all writes to service; keep legacy payment code read-only for historical queries.6. Cleanup & hard delete after reconciliation window; maintain runbook for rollback, manual refunds, and incident responses.Metrics & monitoring- Track success/failure rates, latency, duplicate charges, reconciliation mismatches, PCI alerts.- Automated tests: contract tests, chaos tests, end-to-end payment flows.This plan minimizes customer impact, preserves consistency via idempotency and reconciliation, and limits PCI scope while allowing safe, observable migration.
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