Question: I'd like to ask what is the best way to keep my hadoop cluster safe and schedule periodic backups.
Is it possible to do a live backup of the namenode? How do I set up a backup node?

Answer: 
You can setup a secondary namenode which will automatically take a backup of namenode periodically. In cases of namenode failure, you can use the secondary namenode to regenerate the namenode metadata.

You can also set up HA (high availability) in your cluster, so that if the namenode goes down, the cluster will automatically switch to the the alternate namenode created during HA. Please read more about HA here : <http://hadoop.apache.org/docs/r2.3.0/hadoop-yarn/hadoop-yarn-site/HDFSHighAvailabilityWithNFS.html>
@amar provided a solution to make sure your cluster is highly available. In addition, you should think about how best to protect the data on the Hadoop cluster against user error, logical corruption, disasters and there are different ways to do that. You can write scripts that use HDFS snapshots and distcp to accomplish what you need. If you don't want to write and maintain scripts, you can use solutions like Cloudera BDR or [Talena](http://www.talena-inc.com/product) which offer very comprehensive backup and DR capabilities. Note that I work for Talena.