AWS 角色与密钥

Question

AWS Roles are meant for services which requires access to AWS Services eg S3 etc. using temporary credentials. These are done using STS. This is useful when a user/application from one account needs access to a different account-owned resources on a temporary-basis.

However, STS will only issue a temporary credentials when the credentials are passed using Profile properties. At least that's what the code provided by AWS implies anyway

import com.amazonaws.AmazonServiceException;
import com.amazonaws.SdkClientException;
import com.amazonaws.auth.AWSStaticCredentialsProvider;
import com.amazonaws.auth.BasicSessionCredentials;
import com.amazonaws.auth.profile.ProfileCredentialsProvider;
import com.amazonaws.services.s3.AmazonS3;
import com.amazonaws.services.s3.AmazonS3ClientBuilder;
import com.amazonaws.services.s3.model.ObjectListing;
import com.amazonaws.services.securitytoken.AWSSecurityTokenService;
import com.amazonaws.services.securitytoken.AWSSecurityTokenServiceClientBuilder;
import com.amazonaws.services.securitytoken.model.AssumeRoleRequest;
import com.amazonaws.services.securitytoken.model.AssumeRoleResult;
import com.amazonaws.services.securitytoken.model.Credentials;

public class MakingRequestsWithIAMTempCredentials {
    public static void main(String[] args) {
        String clientRegion = "*** Client region ***";
        String roleARN = "*** ARN for role to be assumed ***";
        String roleSessionName = "*** Role session name ***";
        String bucketName = "*** Bucket name ***";

        try {
            // Creating the STS client is part of your trusted code. It has
            // the security credentials you use to obtain temporary security credentials.
            AWSSecurityTokenService stsClient = AWSSecurityTokenServiceClientBuilder.standard()
                                                    .withCredentials(new ProfileCredentialsProvider())
                                                    .withRegion(clientRegion)
                                                    .build();

            // Obtain credentials for the IAM role. Note that you cannot assume the role of an AWS root account;
            // Amazon S3 will deny access. You must use credentials for an IAM user or an IAM role.
            AssumeRoleRequest roleRequest = new AssumeRoleRequest()
                                                    .withRoleArn(roleARN)
                                                    .withRoleSessionName(roleSessionName);
            AssumeRoleResult roleResponse = stsClient.assumeRole(roleRequest);
            Credentials sessionCredentials = roleResponse.getCredentials();
            
            // Create a BasicSessionCredentials object that contains the credentials you just retrieved.
            BasicSessionCredentials awsCredentials = new BasicSessionCredentials(
                    sessionCredentials.getAccessKeyId(),
                    sessionCredentials.getSecretAccessKey(),
                    sessionCredentials.getSessionToken());

            // Provide temporary security credentials so that the Amazon S3 client 
        // can send authenticated requests to Amazon S3. You create the client 
        // using the sessionCredentials object.
            AmazonS3 s3Client = AmazonS3ClientBuilder.standard()
                                    .withCredentials(new AWSStaticCredentialsProvider(awsCredentials))
                                    .withRegion(clientRegion)
                                    .build();

            // Verify that assuming the role worked and the permissions are set correctly
            // by getting a set of object keys from the bucket.
            ObjectListing objects = s3Client.listObjects(bucketName);
            System.out.println("No. of Objects: " + objects.getObjectSummaries().size());
        }
        catch(AmazonServiceException e) {
            // The call was transmitted successfully, but Amazon S3 couldn't process 
            // it, so it returned an error response.
            e.printStackTrace();
        }
        catch(SdkClientException e) {
            // Amazon S3 couldn't be contacted for a response, or the client
            // couldn't parse the response from Amazon S3.
            e.printStackTrace();
        }
    }
}

The above code will only work without providing some credentials. So my question is, how is Role useful here when I can just simply use access/secret key ?

Answer 1

Exactly the point you mentioned that the credentials are temporary is one of the many reasons why IAM roles are the recommended approach.

A role can be applied to AWS services as well as resources, for example an EC2 instance can have a role attached with AWS automatically rotating these. Additionally you can use STS to assume a role as role, this can be assumed from an IAM user, a role or a federated user .

You should try to avoid using IAM users where possible, there are some usecases such as signed URLs (where you would like it to last more than a few hours) as well as in an on-premise location. If you must use an IAM key you should make sure to rotate the key frequently.

For more information take a look at the IAM Identities (users, groups, and roles) and Security best practices in IAM pages.