code: def _find_usage_instances(self):
          
          # update our limits with usage
          inst_usage = self._instance_usage()
          res_usage = self._get_reserved_instance_count()
          logger.debug('Reserved instance count: %s', res_usage)
          total_ris = 0
          running_ris = 0
          # subtract reservations from instance usage
          ondemand_usage = defaultdict(int)
          for az in inst_usage:
              if az not in res_usage:
                  for i_type, count in inst_usage[az].items():
                      ondemand_usage[i_type] += count
                  continue
              # else we have reservations for this AZ
              for i_type, count in inst_usage[az].items():
                  if i_type not in res_usage[az]:
                      # no reservations for this type
                      ondemand_usage[i_type] += count
                      continue
                  od = count - res_usage[az][i_type]
                  total_ris += res_usage[az][i_type]
                  if count < res_usage[az][i_type]:
                      running_ris += count
                  else:
                      running_ris += res_usage[az][i_type]
                  if od < 0:
                      # we have unused reservations
                      continue
                  ondemand_usage[i_type] += od
          logger.debug(
              'Found %d total RIs and %d running/used RIs',
              total_ris, running_ris
          )
          total_instances = 0
          for i_type, usage in ondemand_usage.items():
              key = 'Running On-Demand {t} instances'.format(
                  t=i_type)
              self.limits[key]._add_current_usage(
                  usage,
                  aws_type='AWS::EC2::Instance',
              )
              total_instances += usage
          # limit for ALL On-Demand EC2 instances
          key = 'Running On-Demand EC2 instances'
          self.limits[key]._add_current_usage(
              total_instances,
              aws_type='AWS::EC2::Instance'
          )
docs: calculate On-Demand instance usage for all types and update Limits