code: @Override
    public List<String> listHosts() {
      try {
        // TODO (dano): only return hosts whose agents completed registration (i.e. has id nodes)
        return provider.get("listHosts").getChildren(Paths.configHosts());
      } catch (KeeperException.NoNodeException e) {
        return emptyList();
      } catch (KeeperException e) {
        throw new HeliosRuntimeException("listing hosts failed", e);
      }
    }
docs: Returns a list of the hosts/agents that have been registered.