code: public synchronized boolean isAllowedHost(String host) {
      boolean isIncluded = includes.isEmpty() || includes.contains(host);
      boolean isExcluded = excludes.contains(host);
      return isIncluded && !isExcluded;
    }
docs: Checks if a host is part of the cluster as per configuration.
  For this the host must be "included" and not "excluded".
  An empty includes files means the host is "included".
  @param host The host name.
  @return A boolean indicating if the host is allowed.