To a node to a cluster without performing rebalance, you use the server-add command:

shell> couchbase-cli server-add -c 192.168.0.1:8091 \
     --server-add=192.168.0.2:8091 -u Administrator -p password

To a node to a cluster and then immediately rebalance the cluster, you use the rebalance command with the --server-add=HOST[:PORT] option. In the option provide the host and port for the node you want to add to the cluster:

shell> couchbase-cli rebalance -c 192.168.0.1:8091 \
     --server-add=192.168.0.2:8091