Ensuring Distributed System Reliability with Jepsen

Jepsen is a framework dedicated to enhancing the safety and reliability of distributed systems, such as databases and consensus algorithms. By rigorously testing these systems under various failure scenarios, Jepsen identifies inconsistencies and potential issues, ensuring that distributed systems perform as intended.

Why Use Jepsen

In distributed systems, ensuring consistency and fault tolerance is paramount. Jepsen provides a structured approach to testing these systems by simulating:

• Network partitions

• Node failures

• Other adverse conditions

This process helps uncover hidden bugs and inconsistencies that might not surface under normal operating conditions.

Jepsen's key benefits include:

• An open-source library offering tools for safety testing.

• Verification of adherence to specified consistency models.

• In-depth analyses to evaluate system claims, uncover new bugs, and provide operator recommendations.

Additionally, Jepsen’s publicly available analyses offer valuable insights into the behavior of various distributed systems. This transparency helps developers and organizations make informed decisions about technologies that align with their consistency and availability requirements.

Use Cases

Jepsen has been instrumental in evaluating a wide range of distributed systems, including:

• Bufstream: In October 2024, Jepsen collaborated with Buf to analyze this Kafka-compatible streaming system. The analysis uncovered safety and liveness issues, such as the loss of acknowledged writes in healthy clusters. These findings led to enhancements in subsequent Bufstream releases.

• MariaDB: Jepsen’s scrutiny of the REPEATABLE READ isolation level revealed it did not provide true repeatable reads. In response, the MariaDB team introduced the --innodb-snapshot-isolation=true flag, which offers Snapshot Isolation at the REPEATABLE READ level.

• FoundationDB: Known for its strong ACID guarantees, FoundationDB underwent rigorous Jepsen testing to verify its fault tolerance and transactional consistency under various failure conditions.

• Riak: This eventually consistent key-value store benefited from Jepsen’s analysis to identify edge cases that could compromise consistency, helping the team refine its operational model.

By identifying critical issues and collaborating with system developers, Jepsen contributes to the enhancement of distributed systems, ensuring they can handle real-world challenges effectively.

Projects Using Jepsen’s Approach

Several notable projects have adopted Jepsen’s approach to ensure their systems’ robustness, including:

• CockroachDB: Extensively uses Jepsen to validate claims of serializable isolation in distributed transactions.

• Apache Cassandra: Jepsen’s tests highlighted areas for improvement in consistency guarantees, leading to further system refinements.

• FoundationDB: Validated its strict ACID properties and fault tolerance through Jepsen simulations.

• Riak: Enhanced its consistency and operational reliability by addressing issues identified through Jepsen tests.

These projects exemplify the value of Jepsen’s methodology in building reliable distributed systems.

How to Use Jepsen

Jepsen is implemented as a Clojure library, and tests are written as Clojure programs. To use Jepsen:

1. Set up a test defining the distributed system under examination, specifying:

   • Operations to execute.

   • Failure scenarios to simulate.

2. Jepsen orchestrates these operations across the system’s nodes, inducing faults and recording the operation history.

3. Analyze the recorded history to verify consistency guarantees under induced failures, identifying deviations from expected behavior.

For detailed guidance, refer to the official documentation and resources on Jepsen’s website. https://jepsen.io/

Watch the video below for a quick intro: Youtube Link to Jespen

Conclusion

Jepsen plays a crucial role in the development and maintenance of robust distributed systems by providing a framework for rigorous testing under adverse conditions. Its recent analyses of systems like Bufstream, MariaDB, FoundationDB, and Riak highlight its impact on improving system reliability and consistency. By utilizing Jepsen, developers and organizations can ensure their distributed systems are resilient, consistent, and capable of meeting real-world demands.