docs: def validate_config(cls, config):
          """
          Validates a config dictionary parsed from a cluster config file.
  
          Checks that a discovery method is defined and that at least one of
          the balancers in the config are installed and available.
          """
          if "discovery" not in config:
              raise ValueError("No discovery method defined.")
  
          installed_balancers = Balancer.get_installed_classes().keys()
  
          if not any([balancer in config for balancer in installed_balancers]):
              raise ValueError("No available balancer configs defined.")