code: func (h *hawkularSink) Register(mds []core.MetricDescriptor) error {
  	// Create model definitions based on the MetricDescriptors
  	for _, md := range mds {
  		hmd := h.descriptorToDefinition(&md)
  		h.models[md.Name] = &hmd
  	}
  
  	if !h.disablePreCaching {
  		// Fetch currently known metrics from Hawkular-Metrics and cache them
  		err := h.cacheDefinitions()
  		if err != nil {
  			return err
  		}
  	}
  
  	return nil
  }
docs: // START: ExternalSink interface implementations