Note that, in the previous playbook, chapter8_8.yml, we have repeated ourselves in the username and password variables for the two devices under the nexus_devices variable:

    vars:
      nexus_devices: {
        "nx-osv-1": {
          "hostname": "nx-osv-1",
          "username": "cisco",
          "password": "cisco",
          "vlans": [100, 200, 300],
        <skip>
        "nx-osv-2": {
          "hostname": "nx-osv-2",
          "username": "cisco",
          "password": "cisco",
          "vlans": [100, 200, 300],
        <skip>

This is not ideal. If we ever need to update the username and password values, we will need to remember to update at two locations. This increases the management burden as well as the chances of making mistakes. For a best practice, Ansible suggests that we use the group_vars and host_vars directories to separate out the variables.