This document discusses using Apache Helix for managing multi-tenant data and applications on YARN. Helix is a generic cluster management framework that handles task and container assignment, failure handling, and workload balancing in a decoupled manner from the core application logic. It provides a high-level overview of key Helix concepts like resources, partitions, and states. The document also outlines how Helix integrates with YARN by using components like the TargetProvider to determine container requirements, Provisioner to acquire/release containers from YARN, and Rebalancer to assign tasks to containers based on constraints. This allows building fault-tolerant applications that can scale efficiently based on workload without having to handle complex cluster management code.