Hello! I've a cluster up and running.
The cluster is running an old CDH version (5.7.0) with 2 NNs and 43 DNs.
Is it possible to install Cloudera Manager?
While it is "possible" , the point of Cloudera Manager is to be that central point for your configurations and manage the cluster. The best option would be to setup another cluster and import your data/config into the Cloudera Manager "managed" cluster.
This has been answered in a previous thread, for review here is the link: