code: func symmetricDifference(hostIDs []string, lbInstances []*cloudstack.VirtualMachine) ([]string, []string) {
  	new := make(map[string]bool)
  	for _, hostID := range hostIDs {
  		new[hostID] = true
  	}
  
  	var remove []string
  	for _, instance := range lbInstances {
  		if new[instance.Id] {
  			delete(new, instance.Id)
  			continue
  		}
  
  		remove = append(remove, instance.Id)
  	}
  
  	var assign []string
  	for hostID := range new {
  		assign = append(assign, hostID)
  	}
  
  	return assign, remove
  }
docs: // symmetricDifference returns the symmetric difference between the old (existing) and new (wanted) host ID's.