This document discusses securing Hadoop and Spark clusters. It begins with an overview of Hadoop security in four steps: authentication, authorization, data protection, and audit. It then discusses specific Hadoop security components like Kerberos, Apache Ranger, HDFS encryption, Knox gateway, and data encryption in motion and at rest. For Spark security, it covers authentication using Kerberos, authorization with Ranger, and encrypting data channels. The document provides demos of HDFS encryption and discusses common gotchas with Spark security.