docs: def get_instances_by_region(self, region):
          ''' Makes an AWS EC2 API call to the list of instances in a particular
          region '''
  
          try:
              conn = self.connect(region)
              reservations = []
              if self.ec2_instance_filters:
                  for filter_key, filter_values in self.ec2_instance_filters.items():
                      reservations.extend(conn.get_all_instances(filters = { filter_key : filter_values }))
              else:
                  reservations = conn.get_all_instances()
  
              for reservation in reservations:
                  for instance in reservation.instances:
                      self.add_instance(instance, region)
  
          except boto.exception.BotoServerError as e:
              if e.error_code == 'AuthFailure':
                  error = self.get_auth_error_message()
              else:
                  backend = 'Eucalyptus' if self.eucalyptus else 'AWS' 
                  error = "Error connecting to %s backend.\n%s" % (backend, e.message)
              self.fail_with_error(error, 'getting EC2 instances')