配置RamRole實現ECS實例的無AK訪問，是真的不需要AK麼？

文檔只配置瞭如下信息，
DefaultProfile profile = DefaultProfile.getProfile("");

    InstanceProfileCredentialsProvider provider = new InstanceProfileCredentialsProvider(
        "<your-role-name>"
    );
    DefaultAcsClient client = new DefaultAcsClient(profile, provider);
    DescribeInstancesRequest request = new DescribeInstancesRequest();
    try {
        DescribeInstancesResponse response = client.getAcsResponse(request);
    } catch (ClientException e) {
        System.err.println(e.toString());
    }

但是JAVA後端卻不能訪問，這種是否也需要子用戶的access Key呢？