Sometimes it has been observed that when we configure and deploy multi-node Hadoop cluster or add new DataNodes, there is an SSH permission issue in communication with Hadoop daemons.
This short article aims to explain how we can resolve the permission issue among DataNodes with NameNode while trying to establish the Secure Shell/SSH without a passphrase. By using DataNode Protocol, all DataNodes talk to the NameNode. By design, the NameNode never initiates any RPCs (Remote Procedure Call). Instead, it only responds to RPC requests issued by DataNodes or clients.