code: def _get_required_params_for_impression(self, experiment, variation_id):
      
      snapshot = {}
  
      snapshot[self.EventParams.DECISIONS] = [{
        self.EventParams.EXPERIMENT_ID: experiment.id,
        self.EventParams.VARIATION_ID: variation_id,
        self.EventParams.CAMPAIGN_ID: experiment.layerId
      }]
  
      snapshot[self.EventParams.EVENTS] = [{
        self.EventParams.EVENT_ID: experiment.layerId,
        self.EventParams.TIME: self._get_time(),
        self.EventParams.KEY: 'campaign_activated',
        self.EventParams.UUID: str(uuid.uuid4())
      }]
  
      return snapshot
docs: Get parameters that are required for the impression event to register.
  
      Args:
        experiment: Experiment for which impression needs to be recorded.
        variation_id: ID for variation which would be presented to user.
  
      Returns:
        Dict consisting of decisions and events info for impression event.