Error Handling and Defensive Programming Questions

Covers designing and implementing defensive, fault tolerant code and system behaviors to prevent and mitigate production failures. Topics include input validation and sanitization, null and missing data handling, overflow and boundary protections, exception handling and propagation patterns, clear error reporting and structured logging for observability, graceful degradation and fallback strategies, retry and backoff policies and idempotency for safe retries. Also address concurrency and synchronization concerns, resource and memory management to avoid exhaustion, security related input checks, and how to document and escalate residual risks. Candidates should discuss pragmatic trade offs between robustness and complexity, show concrete defensive checks and assertions, and describe test strategies for error paths including unit tests and integration tests and how monitoring and operational responses tie into robustness.

MediumSystem Design

0 practiced

Outline a canary deployment strategy for a web service that reduces risk during feature rollouts. Include traffic split plan, instrumentation to compare canary vs baseline metrics, automated rollback triggers (error budget, latency regressions), and how you would test the canary pipeline end-to-end before production.

HardTechnical

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Design a chaos engineering game-day plan focused on error handling and defensive programming. List specific experiments (network latency, connection resets, slow DB, OOM-kill), blast radius controls, success criteria tied to SLOs, rollback steps, and how to turn findings into actionable work items.

EasyTechnical

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Explain idempotency in distributed systems. Provide three techniques to achieve idempotent operations (idempotency keys with stored responses, unique constraints/de-duplication at the database level, and write-once semantics) and discuss the trade-offs (storage cost, expiration, concurrency).

MediumTechnical

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Design and provide pseudocode for an idempotent POST endpoint for a payments service that accepts an 'Idempotency-Key' header. Requirements: ensure at-most-once effect or consistent responses on retries, handle concurrent requests with the same key, expire keys after 24 hours, and store enough response metadata to replay identical responses. Describe storage and locking choices.

HardTechnical

0 practiced

You're investigating a production outage where clients retried rapidly and downstream databases were overloaded, causing cascading failures. Outline a post-incident action plan: root-cause analysis steps, immediate mitigations (throttling, disable retries), medium-term fixes, monitoring improvements, and policy changes to prevent recurrence.

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