code: def get_eni_id(self, interface=1):
          
          log = logging.getLogger(self.cls_logger + '.get_eni_id')
  
          # Get the instance-id
          if self.instance_id is None:
              msg = 'Instance ID not found for this machine'
              log.error(msg)
              raise OSError(msg)
          log.info('Found instance ID: {i}'.format(i=self.instance_id))
  
          log.debug('Querying EC2 instances...')
          try:
              response = self.client.describe_instances(
                      DryRun=False,
                      InstanceIds=[self.instance_id]
              )
          except ClientError:
              _, ex, trace = sys.exc_info()
              msg = 'Unable to query EC2 for instances\n{e}'.format(e=str(ex))
              log.error(msg)
              raise AWSAPIError, msg, trace
          log.debug('Found instance info: {r}'.format(r=response))
  
          # Find the ENI ID
          log.info('Looking for the ENI ID to alias...')
          eni_id = None
          try:
              for reservation in response['Reservations']:
                  for instance in reservation['Instances']:
                      if instance['InstanceId'] == self.instance_id:
                          for network_interface in instance['NetworkInterfaces']:
                              if network_interface['Attachment']['DeviceIndex'] == interface:
                                  eni_id = network_interface['NetworkInterfaceId']
          except KeyError:
              _, ex, trace = sys.exc_info()
              msg = 'ENI ID not found in AWS response for interface: {i}'.format(i=interface)
              log.error(msg)
              raise EC2UtilError, msg, trace
  
          log.info('Found ENI ID: {e}'.format(e=eni_id))
          return eni_id
docs: Given an interface number, gets the AWS elastic network
          interface associated with the interface.
  
          :param interface: Integer associated to the interface/device number
          :return: String Elastic Network Interface ID or None if not found
          :raises OSError, AWSAPIError, EC2UtilError