This MLS-C01 practice question tests your understanding of data engineering. 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 data engineer runs the AWS CLI command above to inspect a file in S3. They need to determine if the file was modified after a Glue ETL job processed it. What additional information could they obtain from this command?
The object's content type.
Why wrong: Content type is not shown in this output.
The object's storage class.
Why wrong: Storage class is not included in the output of head-object unless requested.
The object's last modified timestamp.
The LastModified field indicates when the object was last modified.
The object's ETag.
Why wrong: ETag is shown but does not help determine modification time.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The object's last modified timestamp.
The AWS CLI command `aws s3api head-object --bucket my-bucket --key my-key` returns metadata about an S3 object without downloading it. The `LastModified` field in the response provides the exact timestamp of the last modification, which can be compared to the Glue ETL job's execution time to determine if the file was modified after processing. This is the only field that directly answers the question about modification timing.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
The object's content type.
Why it's wrong here
Content type is not shown in this output.
The object's storage class.
Why it's wrong here
Storage class is not included in the output of head-object unless requested.
The object's last modified timestamp.
Why this is correct
The LastModified field indicates when the object was last modified.
Related concept
Read the scenario before looking for a memorised answer.
The object's ETag.
Why it's wrong here
ETag is shown but does not help determine modification time.
Common exam traps
The trap here is that candidates may confuse the `ETag` (a content hash) with a modification timestamp, or assume that `head-object` returns only basic metadata like size and type, overlooking the `LastModified` field that directly answers the question.
Trap categories for this question
Command / output trap
Content type is not shown in this output.
Detailed technical explanation
The `head-object` command uses the S3 REST API HEAD operation, which returns the `Last-Modified` header as an HTTP-date (e.g., 'Thu, 15 Dec 2022 12:00:00 GMT'). This timestamp is set by S3 when the object is uploaded or overwritten, and it is not affected by metadata updates or lifecycle transitions. In a real-world scenario, a Glue ETL job might record its completion time in a DynamoDB table or CloudWatch log, and comparing that to the `LastModified` value from `head-object` is a common pattern for incremental processing.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
| 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 |
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FAQ
Data Engineering — This question tests Data Engineering — Read the scenario before looking for a memorised answer..
The correct answer is: The object's last modified timestamp. — The AWS CLI command `aws s3api head-object --bucket my-bucket --key my-key` returns metadata about an S3 object without downloading it. The `LastModified` field in the response provides the exact timestamp of the last modification, which can be compared to the Glue ETL job's execution time to determine if the file was modified after processing. This is the only field that directly answers the question about modification timing.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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