Does Insight need to be enabled all the nodes in the cluster, if I want to run report or use insight DB for client session/bandwidth limit?
It is not required to enable Insight on all the nodes in a Cluster. Just have it enabled in 2 nodes per cluster, so that you will have one primary/master and a backup.
The nodes that are enabled with Insight will be considered as netevent targets by all the nodes in the cluster. And all the nodes will send the Insight data to the netevent targets.
Consider you have 8 nodes cluster and the Insight is enabled on node 1 and node 2. The nodes 1 and 2 will be considers as netevent targets for all the 8 nodes(including node 1 and 2) and all the 8 nodes will send the events/insight data to the targets.
You can login to the Insight GUI in a node that has insight enable and run the reports.