I'm trying to upgrade one of my physical host to add more memory.
I would like to know what's the best practise to achieve this.
If you can schedule downtime for your entire Hadoop cluster, and stop all services, that would be the easiest.
You can do that easily from Cloudera Manager.
Otherwise you first need to check what Hadoop services are running on that host, and think carefully how shutting down services on that host could affect other parts of the cluster.