I Need to setup 10 DN's, 1 NN , 1 Standby NN to be configured in a cluster with ambari. can i have both ambari manager and Namenode on same server or is it recommended to keep it separate servers ?
By Ambari Manager do you mean Ambari Server?
Yes, Ambari Server can be be installed on the same node as NameNode. It is not mandatory to have a separate dedicated server for ambari.
However if you are going to have a very huge cluster with lots of data then it will be good to install the AmbariServer on any EdgeNode or DataNode host, Because if there are less system resources available on the NameNode host (like CPU/RAM/IO) then better to install AmbariServer on a different node.