@Override
  public List<ServerLocation> getAllServers() {
    if (PoolImpl.TEST_DURABLE_IS_NET_DOWN) {
      return null;
    }
    GetAllServersRequest request = new GetAllServersRequest(serverGroup);
    GetAllServersResponse response = (GetAllServersResponse) queryLocators(request);
    if (response != null) {
      return response.getServers();
    } else {
      return null;
    }
  }
key is the InetSocketAddress of the locator. value will be an exception if we have already
found the locator to be dead. value will be null if we last saw it alive.
geode-core/src/main/java/org/apache/geode/cache/client/internal/AutoConnectionSourceImpl.java