public void stopServers() throws IOException {
    if (serverInitialized) {
      logger.info("Stopping servers......");
      CountDownLatch shutdownLatch = new CountDownLatch(serverList.size());
      for (AmbryServer server : serverList) {
        new Thread(new ServerShutdown(shutdownLatch, server)).start();
      }
      try {
        if (!shutdownLatch.await(3, TimeUnit.MINUTES)) {
          fail("Did not shutdown in 1 minute");
        }
      } catch (Exception e) {
        throw new IOException(e);
      }
      serverInitialized = false;
    }
  }
Shut down all the servers but keep the cluster.
@throws IOException
ambry-test-utils/src/main/java/com/github/ambry/server/MockCluster.java