This document discusses challenges with online patching in Oracle E-Business Suite release 12.2.5. It begins with an overview of the 12.2 architecture and how it enables features like file system editioning and database edition-based redefinition to allow patching while the application is online. It then covers the online patching cycle in detail and discusses options for developing custom code to be either fully or runtime compliant. The document concludes with lessons learned around areas like database object grants, the DB_Domain parameter, executing autoconfig, and administering application nodes. It also discusses some common challenges seen with online patching and useful utilities for monitoring and diagnosing issues.