If you have an existing deployment of Group Replication and you want to manage it using the MySQL Shell, the option adoptFromGR from the dba.createCluster() function can be used.

shell> mysqlsh --uri [email protected]:3306
  Creating a Session to '[email protected]:3306'
  Enter password: ****
  Classic Session successfully established. No default schema selected.

MySQL Shell JavaScript Code:

mysql-js> var cluster = dba.createCluster('prodCluster', {adoptFromGR: true});

  A new InnoDB cluster will be created on instance '[email protected]:3306'.

  Creating InnoDB cluster 'prodCluster' on '[email protected]:3306'...
  Adding Seed Instance...

  Cluster successfully created. Use cluster.addInstance() to add MySQL instances.
  At least 3 instances are needed for the cluster to be able to withstand up to
  one server failure.

mysql-js> cluster.describe();
{
  "clusterName": "prodCluster",
  "adminType": "local",
  "defaultReplicaSet": {
      "name": "default",
      "instances": [
        {
          "name": "localhost:3306",
          "host": "localhost:3306",
          "role": "HA"
        },
        {
          "name": "localhost:3307",
          "host": "localhost:3307",
          "role": "HA"
        },
        {
          "name": "localhost:3308",
          "host": "localhost:3308",
          "role": "HA"
        }
     ]
  }
}