配置RamRole实现ECS实例的无AK访问，是真的不需要AK么？

文档只配置了如下信息，

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());
}</code></pre>                

但是JAVA后端却不能访问，这种是否也需要子用户的access Key呢？