Introducing Zelos: A ZooKeeper API leveraging Delos

Introduced Zelos, a ZooKeeper API built on the Delos distributed system platform. Zelos aims to replace Meta's existing ZooKeeper clusters by providing a more modular, extensible, and performant variant. Key technical contributions include addressing the impedance mismatch between ZooKeeper's session management and Delos's linearizable log by implementing speculative execution for session ordering and a RequestProcessor for ordering reads within sessions. It also details the challenges and solutions for transparently migrating ZooKeeper-based applications to the new Zelos architecture.