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Question 1,588 of 1,748

Identity and Access Management →mediumMultiple ChoiceObjective-mapped

Cross-Account IAM Role for EC2 to S3

This SCS-C02 practice question tests your understanding of identity and access management. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

A company uses IAM roles for EC2 instances. An application running on an EC2 instance needs to read from an S3 bucket in another AWS account. What is the most secure way to grant access?

A
Create an IAM role in the target account with read access to the bucket, and allow the EC2 instance's role to assume it.
Uses cross-account role assumption, following security best practices.
B
Store the other account's IAM user access keys in the EC2 instance.
Why wrong: Insecure; long-term credentials should not be stored on instances.
C
Make the bucket public.
Why wrong: Public access is not secure and violates best practices.
D
Create a bucket policy that allows access from the EC2 instance's public IP.
Why wrong: Using IP addresses is less secure and not recommended for cross-account access.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

Create an IAM role in the target account with read access to the bucket, and allow the EC2 instance's role to assume it.

Option A is correct because using a cross-account IAM role in the target account allows the EC2 instance to assume the role and access the bucket securely, without sharing long-term credentials. This follows the principle of least privilege and avoids storing permanent credentials on the instance. Option B is insecure as it stores long-term IAM user access keys on the instance, which could be compromised. Option C makes the bucket public, violating security. Option D relies on the instance's public IP, which is not a secure access control mechanism and can change.

Key principle: Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✓
Create an IAM role in the target account with read access to the bucket, and allow the EC2 instance's role to assume it.
Why this is correct
Uses cross-account role assumption, following security best practices.
Related concept
Authentication checks who the user is.
✗
Store the other account's IAM user access keys in the EC2 instance.
Why it's wrong here
Insecure; long-term credentials should not be stored on instances.
✗
Make the bucket public.
Why it's wrong here
Public access is not secure and violates best practices.
✗
Create a bucket policy that allows access from the EC2 instance's public IP.
Why it's wrong here
Using IP addresses is less secure and not recommended for cross-account access.

Common exam traps

Common exam trap: authentication is not authorization

Logging in proves the user can authenticate. It does not automatically mean the user is allowed to enter privileged or configuration mode. Watch for AAA authorization, privilege level and command authorization details.

Detailed technical explanation

How to think about this question

This kind of question is testing the difference between identity and permission. A user may successfully log in to a router because authentication is working, but still fail to enter configuration mode because authorization is missing, misconfigured or mapped to a lower privilege level.

KKey Concepts to Remember

Authentication checks who the user is.
Authorization controls what the user is allowed to do after login.
Privilege levels affect access to EXEC and configuration commands.
AAA, TACACS+ and RADIUS can separate login success from command access.

TExam Day Tips

Do not assume successful login means full administrative access.
Look for words such as cannot enter configuration mode, privilege level, authorization or command access.
Separate login problems from permission problems before choosing the answer.

Key takeaway

Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.

Real-world example

How this comes up in practice

A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.

Quick reference

AWS S3 Storage Class Comparison

Storage Class	Min Duration	Retrieval	Use Case
S3 Standard	None	Immediate	Frequently accessed data
S3 Standard-IA	30 days	Immediate	Infrequent access, rapid retrieval
S3 One Zone-IA	30 days	Immediate	Non-critical infrequent data
S3 Intelligent-Tiering	None	Immediate–hours	Unknown or changing access patterns
S3 Glacier Instant	90 days	Milliseconds	Archive with instant retrieval
S3 Glacier Flexible	90 days	Minutes–hours	Archive, flexible retrieval
S3 Glacier Deep Archive	180 days	Hours	Long-term compliance archive

What to study next

Got this wrong? Here's your next step.

Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related SCS-C02 questions on access control and AAA configuration.

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FAQ

Questions learners often ask

What does this SCS-C02 question test?

Identity and Access Management — This question tests Identity and Access Management — Authentication checks who the user is..

What is the correct answer to this question?

The correct answer is: Create an IAM role in the target account with read access to the bucket, and allow the EC2 instance's role to assume it. — Option A is correct because using a cross-account IAM role in the target account allows the EC2 instance to assume the role and access the bucket securely, without sharing long-term credentials. This follows the principle of least privilege and avoids storing permanent credentials on the instance. Option B is insecure as it stores long-term IAM user access keys on the instance, which could be compromised. Option C makes the bucket public, violating security. Option D relies on the instance's public IP, which is not a secure access control mechanism and can change.

What should I do if I get this SCS-C02 question wrong?

What is the key concept behind this question?

Authentication checks who the user is.

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