Once you built a cluster, the first thing you thought about was how to secure it, right? Don't worry, most people don't. But, as Hadoop has moved on from being something running in-house analysis in the research department to directly driving critical systems, it's not something to ignore for too long.
Securing Hadoop is not something to be done on a whim or without significant testing. We cannot give detailed advice on this topic and cannot stress strongly enough the need to take this topic seriously and do it properly. It might consume time, it might cost money, but weigh this against the cost of having your cluster compromised.
Security is also a much bigger topic than just the Hadoop cluster. We'll explore some of the security features available in Hadoop, but you do need a coherent security strategy into which these discrete components fit.