anchor.diff:      response = client.describe_instances(InstanceIds=[instance_id])
       key = 'PrivateDnsName'
       host = response['Reservations'][0]['Instances'][0]['NetworkInterfaces'][0]
  +
       if not key in host:
           print("The instance attribute {} does not exist".format(key))
           exit(1)
  
positive.code:                    ]
                 )
  
      nodes = response['Reservations']
  
      return [
          "%s:%s" % (
              instance['Instances'][0]['PrivateDnsName'],
              next(
                  filter(
                      lambda t: t['Key'] == 'aws_hostname',
                      instance['Instances'][0]['Tags']
                  )
              )['Value']
          )
          for instance in list(nodes)
      ]
  
  def ec2_classes(stackname):
  
negative.code:                    ]
                 )
  
      hosts = []
  
      reservations = response['Reservations']
      for reservation in reservations:
          instances = reservation['Instances']
          for instance in instances:
              hosts.append((instance['PrivateDnsName']))
  
      return(hosts)
  
  