Json:
{
"vdd": {
    "sites": {
      "drupal8": {
        "account_name": "root",
        "account_pass": "root",
        "account_mail": "[email protected]",
        "site_name": "Drupal 8",
        "site_mail": "[email protected]",
        "vhost": {
          "document_root": "drupal8",
          "url": "drupal8.dev",
          "alias": ["www.drupal8.dev"]
        }
      },
      "drupal7": {
        "account_name": "root",
        "account_pass": "root",
        "account_mail": "[email protected]",
        "site_name": "Drupal 7",
        "site_mail": "[email protected]",
        "vhost": {
          "document_root": "drupal7",
          "url": "drupal7.dev",
          "alias": ["www.drupal7.dev"]
        }
      }
    }
  }
}

ruby code to get each url:
config_json["vdd"]["sites"].each_with_index do |site, idx|
    puts site[idx]["vhost"]['url'] // ERROR
end