The answer is ecr:GetDownloadUrlForLayer and ecr:BatchGetImage on the ECR repository. These two permissions are required because when SageMaker launches a training job, it must first retrieve the image metadata and layer manifests via BatchGetImage, then generate pre-signed URLs for each layer download using GetDownloadUrlForLayer—without both, the pull fails with an AccessDenied error. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this scenario tests your understanding of how SageMaker execution roles interact with ECR, often appearing as a trick where only ecr:BatchGetImage is listed, omitting the critical GetDownloadUrlForLayer. A common trap is assuming ecr:GetAuthorizationToken alone suffices, but that token is for the Docker CLI, not for SageMaker’s internal pull mechanism. Remember the mnemonic “Batch then URL” to recall that SageMaker needs both the image batch metadata and the layer download URLs.
MLS-C01 Practice Question: Machine Learning Implementation and Operations
This MLS-C01 practice question tests your understanding of machine learning implementation and operations. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
An IAM policy is attached to a SageMaker execution role. A data scientist tries to create a training job using a custom algorithm stored in an ECR repository. The training job fails with an 'AccessDenied' error when pulling the Docker image from ECR. What is the missing permission?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ecr:GetDownloadUrlForLayer and ecr:BatchGetImage on the ECR repository
When SageMaker pulls a custom Docker image from ECR during training job creation, the execution role needs permissions to download the image layers. The required actions are ecr:GetDownloadUrlForLayer (to generate pre-signed URLs for each layer) and ecr:BatchGetImage (to retrieve image metadata and layer manifests). Without these, the 'AccessDenied' error occurs because SageMaker cannot authenticate or fetch the container image from the ECR repository.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
ecr:GetDownloadUrlForLayer and ecr:BatchGetImage on the ECR repository
Why this is correct
These permissions are required to pull a Docker image from ECR.
Related concept
Read the scenario before looking for a memorised answer.
✗
ecr:PutImage on the ECR repository
Why it's wrong here
PutImage is for pushing, not pulling images.
✗
s3:GetObject on the ECR repository
Why it's wrong here
ECR is not S3.
✗
sagemaker:CreateTrainingJob on the ECR resource
Why it's wrong here
CreateTrainingJob is for the SageMaker API, not ECR.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse ECR pull permissions with S3 permissions (option C) or assume that the SageMaker CreateTrainingJob permission (option D) implicitly covers the ECR pull, when in fact the IAM role must explicitly grant the specific ECR read actions for image retrieval.
Detailed technical explanation
How to think about this question
ECR uses a token-based authentication system where the Docker client (or SageMaker) first calls ecr:GetAuthorizationToken to obtain a temporary password, then uses that token to call ecr:BatchGetImage and ecr:GetDownloadUrlForLayer. The GetDownloadUrlForLayer action returns a pre-signed S3 URL that points to the actual layer blob stored in an S3 bucket managed by ECR, but the permission is still an ECR action, not an S3 action. In cross-account scenarios, the ECR repository policy must also grant cross-account access, and the execution role must have the correct trust relationship.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Machine Learning Implementation and Operations — This question tests Machine Learning Implementation and Operations — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: ecr:GetDownloadUrlForLayer and ecr:BatchGetImage on the ECR repository — When SageMaker pulls a custom Docker image from ECR during training job creation, the execution role needs permissions to download the image layers. The required actions are ecr:GetDownloadUrlForLayer (to generate pre-signed URLs for each layer) and ecr:BatchGetImage (to retrieve image metadata and layer manifests). Without these, the 'AccessDenied' error occurs because SageMaker cannot authenticate or fetch the container image from the ECR repository.
What should I do if I get this MLS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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