Jeff’s Note #
Unlike generic exam dumps, ADH analyzes this scenario through the lens of a Real-World Lead Developer.
For DVA-C02 candidates, the confusion often lies in misunderstanding how IAM roles and bucket policies govern S3 access from EC2 instances. In production, this is about knowing exactly which identity has permission and how that translates to API calls your application issues. Let’s drill down.
The Certification Drill (Simulated Question) #
Scenario #
BrightApps Inc. is building a data processing application that runs on Amazon EC2 Linux instances. During integration testing, the application fails to retrieve files from a specific Amazon S3 bucket and logs “Access Denied” errors. The networking team confirms that the EC2 instances have outbound internet access, and connectivity tests to S3 endpoints succeed.
The Requirement: #
Determine the best two steps the BrightApps DevOps team should take to troubleshoot and fix the S3 access issue.
The Options #
- A) Verify that the IAM role attached to the EC2 instances has a policy granting the required S3 access permissions.
- B) Review the Amazon S3 bucket policy to check if it explicitly allows access from the EC2 IAM role or the application’s principal.
- C) Investigate whether the IAM user credentials embedded on the EC2 instances have permissions to access the S3 bucket.
- D) Examine the S3 bucket lifecycle policy to confirm if it restricts permissions for active objects.
- E) Inspect the EC2 security groups to ensure there are no rules blocking outbound traffic to Amazon S3 endpoints.
Google adsense #
leave a comment:
Correct Answer #
A and B.
Quick Insight: The Developer’s IAM Permissions Imperative #
Unlike user credentials, applications running on EC2 commonly rely on instance profile IAM roles for permissions.
Access is allowed only if both the IAM role’s policies and the bucket policy (if any) permit it.
Network connectivity alone does not guarantee access — permission configurations govern the actual authorization.
Content Locked: The Expert Analysis #
You’ve identified the answer. But do you know the implementation details that separate a Junior from a Senior?
The Expert’s Analysis #
Correct Answer #
Options A and B
The Winning Logic #
- Option A: The EC2 instance needs an attached IAM role with a policy granting S3 permissions (e.g.,
s3:GetObject). Because EC2 instances access AWS resources using their instance profile role, missing or insufficient permissions here will cause access failures. - Option B: Even when the IAM role allows access, the S3 bucket policy might restrict which principals can read from the bucket. Checking the bucket policy and ensuring that the IAM role’s ARN (or appropriate principal) is allowed is critical.
The Trap (Distractor Analysis) #
- Why not C? EC2 instances do not use an IAM user for accessing S3. Inline or stored IAM user credentials are discouraged and would require manual embedding, which is not standard. Permissions should be tied to the instance’s IAM role, not a user.
- Why not D? The S3 lifecycle policy controls data retention and transitions (e.g., moving objects to Glacier), not access permissions. It has no bearing on read or write permissions.
- Why not E? Security groups control network traffic at the instance level. Since S3 is a managed AWS service endpoint reachable over the internet or VPC endpoints, security groups rarely block outbound HTTPS requests to S3. Also, the question confirms connectivity is not an issue.
The Technical Blueprint #
For Developer / SysOps (Code/CLI Snippet):
# Check attached role to EC2 instance:
INSTANCE_ID="i-0123456789abcdef0"
ROLE_NAME=$(aws ec2 describe-instances --instance-ids $INSTANCE_ID \
--query "Reservations[0].Instances[0].IamInstanceProfile.Arn" --output text | cut -d/ -f2)
# List policies attached to the IAM role
aws iam list-attached-role-policies --role-name $ROLE_NAME
# Get inline policies and their contents
aws iam get-role-policy --role-name $ROLE_NAME --policy-name YourPolicyName
# Simulate access to S3 with role permissions:
aws sts get-caller-identity
aws s3api get-object --bucket your-bucket-name --key test-object test-object.out
The Comparative Analysis #
| Option | API/Permission Focus | Common Usage Scenario | Why it’s Correct/Incorrect |
|---|---|---|---|
| A | IAM Role permissions | EC2 uses instance profile roles for AWS creds | Correct: Primary access check |
| B | S3 Bucket policy permissions | Bucket can restrict access regardless of IAM role | Correct: Needed if the bucket denies access |
| C | IAM User permissions | Not applicable when EC2 uses roles | Incorrect: IAM user irrelevant here |
| D | S3 Lifecycle policies | Controls data transitions, not permissions | Incorrect: No effect on access |
| E | Security Groups (network ACL) | Controls instance network traffic | Incorrect: Connectivity confirmed not an issue |
Real-World Application (Practitioner Insight) #
Exam Rule #
For the exam, always check both the IAM role policies attached to the EC2 instance and the S3 bucket policy when diagnosing access issues.
Real World #
In production, developers sometimes hardcode IAM user keys on EC2 instances (not recommended). This is a security risk and often creates debugging headaches when the IAM role is expected but not configured.
(CTA) Stop Guessing, Start Mastering #
Disclaimer
This is a study note based on simulated scenarios for the AWS DVA-C02 exam.