code: def api_version_elb_backend(*args, **kwargs):
      
      request = args[0]
  
      if hasattr(request, 'values'):
          # boto3
          version = request.values.get('Version')
      elif isinstance(request, AWSPreparedRequest):
          # boto in-memory
          version = parse_qs(request.body).get('Version')[0]
      else:
          # boto in server mode
          request.parse_request()
          version = request.querystring.get('Version')[0]
  
      if '2012-06-01' == version:
          return ELBResponse.dispatch(*args, **kwargs)
      elif '2015-12-01' == version:
          return ELBV2Response.dispatch(*args, **kwargs)
      else:
          raise Exception("Unknown ELB API version: {}".format(version))
docs: ELB and ELBV2 (Classic and Application load balancers) use the same
      hostname and url space. To differentiate them we must read the
      `Version` parameter out of the url-encoded request body. TODO: There
      has _got_ to be a better way to do this. Please help us think of
      one.