The answer is to use S3 bucket policies for cross-account access and IAM policies for user-level control, as these are the two standard, non-legacy methods for managing access to a data lake. S3 bucket policies are resource-based, allowing you to grant permissions to principals from other AWS accounts, while IAM policies are identity-based, attaching directly to users, groups, or roles within your own account. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this distinction tests your understanding of the shared responsibility model and how to secure a data lake at scale, often appearing in scenario-based questions where you must choose between ACLs (which are deprecated), pre-signed URLs (temporary only), and encryption options (which protect data at rest, not access). A common trap is confusing SSE-S3 encryption with access control—remember that encryption governs confidentiality, not who can read or write. Memory tip: IAM for identities, bucket policies for resources, and never touch ACLs for new designs.
MLS-C01 Data Engineering Practice Question
This MLS-C01 practice question tests your understanding of data engineering. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Which TWO options are best practices for managing access to data stored in Amazon S3 for a data lake?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use IAM policies to control user and role permissions
IAM policies and bucket policies are standard for access control. S3 ACLs are legacy and not recommended. SSE-S3 is encryption, not access control. Pre-signed URLs are for temporary access, not general governance.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Use S3 access control lists (ACLs) for granular permissions
Why it's wrong here
ACLs are outdated; AWS recommends IAM and bucket policies.
✗
Enable default encryption with SSE-S3
Why it's wrong here
Encryption protects data at rest, not access control.
✓
Use IAM policies to control user and role permissions
Why this is correct
IAM policies are central to access management.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✓
Use S3 bucket policies to grant cross-account access
The clue word "best" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
Generate pre-signed URLs for all data access
Why it's wrong here
Pre-signed URLs are for specific temporary access, not a general access control mechanism.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related MLS-C01 ACL questions on filtering logic and placement.
Data Engineering — This question tests Data Engineering — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Use IAM policies to control user and role permissions — IAM policies and bucket policies are standard for access control. S3 ACLs are legacy and not recommended. SSE-S3 is encryption, not access control. Pre-signed URLs are for temporary access, not general governance.
What should I do if I get this MLS-C01 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related MLS-C01 ACL questions on filtering logic and placement.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Standard ACLs match source addresses.
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