How etcd Solved Its Knowledge Drain with Deterministic Testing

The etcd project — a distributed key-value store older than Kubernetes — recently faced significant challenges due to maintainer turnover and the resulting loss of unwritten institutional knowledge. Lead maintainer Marek Siarkowicz explained that as longtime contributors left, crucial expertise about testing procedures and correctness guarantees disappeared. This gap led to a problematic release that introduced critical reliability issues, including potential data inconsistencies after crashes.

To rebuild confidence in etcd’s correctness, the new maintainer team introduced “robustness testing,” creating a framework inspired by Jepsen to validate both basic and distributed-system behavior. Their goal was to ensure linearizability, the “Holy Grail” of distributed systems, which required developing custom failure-injection tools and teaching the community how to debug complex scenarios.

The team later partnered with Antithesis to apply deterministic simulation testing, enabling fully reproducible execution paths and easier detection of subtle race conditions. This approach helped codify implicit knowledge into explicit properties and assertions. Siarkowicz emphasized that such rigorous testing is essential for safeguarding the sensitive “core” of large open source projects, ensuring correctness even as maintainers change.

Learn more from The New Stack about the etcd project

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