# A downstream tax API has been failing for 15 minutes Canonical URL: Domain: Pipeline Design ยท Difficulty: medium ## Problem A downstream tax API has been failing for 15 minutes. Every worker keeps issuing requests; each waits the full 30-second timeout before failing; the pipeline burns compute on a service that cannot serve. The section's pattern is the circuit breaker: a wrapper around the downstream call that tracks failure rate and, when threshold is crossed, refuses to call for a cool-down. Trial requests after the cool-down decide whether to close again or stay open. Open the breaker by adding one between the worker and the tax API whose name states the three states and their transition parameters. ## Related - [All practice problems](https://datadriven.io/problems) - [Mock interview mode](https://datadriven.io/interview/a-downstream-tax-api-has-been-failing-for-15-minutes-every-936d1e2e) - [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.