why there need to check standby_host before create connect

[wfxxh]

# Create and test standby client if configured.
if @standby_host
  @standby_client = prepare_client(@standby_host, @standby_port, @user)
  begin
    test_client(@standby_client)
  rescue => e
    logger.warn("Could not connect to standby namenode #{@standby_client.host}. Error: #{e.message}. Trying main webhdfs namenode.")
  end
end
@client = prepare_client(@host, @port, @user)
begin
  test_client(@client)
rescue => e
  # If no standy host is configured, we need to exit here.
  if not @standby_host
    raise
  else
    # If a standby host is configured, try this before giving up.
    logger.error("Could not connect to #{@client.host}:#{@client.port}. Error: #{e.message}")
    do_failover
  end
end