Important
A 'node key' is associated with only one node, so for creating 'N' nodes, you need 'N' node keys
In a ledger, each process is not just identified by 'IP:port', but with a specific node-key too, so IP address can change for the given process over time, but node-key is considered as the exact process w.r.to ledger.
docker run -i -v $(pwd):/data dhiway/cord:0.9.0 key generate-node-key --file /data/node.key
This above command gives the output of public information of nodeKey, something like 12D3KooWMzmZ2g7LBPQuTBsb2HVTszsAToSzXuJJNQzHvbPKWbnq. This also needs to be stored securely. Also note, similar to key generate, generate-node-key too generates a random key for every invocation.