# A consumer-app event pipeline has every beginner-tier failure mode at once: producers ship new field Canonical URL: Domain: Pipeline Design ยท Difficulty: medium ## Problem A consumer-app event pipeline has every beginner-tier failure mode at once: producers ship new fields without warning, the loader is strict and rejects unexpected payloads, the daily aggregation buckets by processing_time so late mobile events land in the wrong day, and there is no rerun window so each day's number freezes once it is written. The capstone is the assembled fix from the four beginner sections. Replace the strict loader and warehouse with a flexible-shape destination (lakehouse format with schema_evolution, or VARIANT-typed warehouse columns) so producer additions absorb without code changes; rebucket the aggregation by event_time; add an orchestrator with a seven-day rerun window in its name; replace the append-only destination with one that supports partition overwrite by event_date so reruns are idempotent. The dashboard must read from the final reconciled destination. ## Related - [All practice problems](https://datadriven.io/problems) - [Mock interview mode](https://datadriven.io/interview/a-consumer-app-event-pipeline-has-every-beginner-tier-failur-bf6d5331) - [System Design Interview Questions](https://datadriven.io/data-engineering-system-design) - [Data Engineering Interview Prep Guide](https://datadriven.io/data-engineer-interview-prep) - [Daily Challenge](https://datadriven.io/daily) --- Source: DataDriven (https://datadriven.io). 100% free data engineering interview prep. Live code execution against Postgres 16, Python 3.11, and Spark sandboxes. No paywall, no premium tier, no signup gate.