Often in test clusters and tests, we start multiple datanodes on the same host.
In SCMNodeManager.register() there is a map of hostname -> datanode UUID called dnsToUuidMap.
If several DNs register from the same host, the entry in the map will be overwritten and the last DN to register will 'win'.
This means that the method getNodeByAddress() does not return the correct DatanodeDetails object when many hosts are registered from the same address.
This method is only used in SCMBlockProtocolServer.sortDatanodes() to allow it to see if one of the nodes matches the client, but it need to be used by the Decommission code.
Perhaps we could change the getNodeByAddress() method to returns a list of DNs? In normal production clusters, there should only be one returned, but in test clusters, there may be many. Any code looking for a specific DN entry would need to iterate the list and match on the port number too, as host:port would be the unique definition of a datanode.