# A four-year-old Kafka topic carries customer events with no formal schema, three named consumers, an Canonical URL: Domain: Pipeline Design ยท Difficulty: medium ## Problem A four-year-old Kafka topic carries customer events with no formal schema, three named consumers, and an unknown number of analyst queries. One wrong-number incident every six to eight weeks. Producers have added and renamed fields without coordination. The section's rollout is four steps: document the current contract (1.0.0) capturing reality not aspiration, inventory every consumer, observe the contract in shadow mode before enforcing, then migrate behind versioned changes. Plan the rollout by adding the four-step pipeline to the canvas: a documented-contract artifact, a consumer-inventory artifact, a shadow-mode observation transform, and a versioned-enforcement gate that activates only after the inventory and observation steps complete. ## Related - [All practice problems](https://datadriven.io/problems) - [Mock interview mode](https://datadriven.io/interview/a-four-year-old-kafka-topic-carries-customer-events-with-no-ab6d1993) - [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.