The answer is that the policy lacks the required `kms:Decrypt` permission for the KMS key. When a parameter is stored as a SecureString in SSM Parameter Store, AWS KMS automatically encrypts the value at rest, and any retrieval action—even `ssm:GetParameter`—triggers a decryption operation behind the scenes. Without explicit `kms:Decrypt` access on the customer managed key used to encrypt the parameter, the API call fails, even if the SSM actions and resource ARN are correctly configured. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of the dependency between Systems Manager and KMS for encrypted parameters, a common trap where candidates focus only on SSM permissions and overlook the encryption layer. A reliable memory tip is “SecureString = SSM + KMS: you need both Get and Decrypt.”
DOP-C02 Configuration Management and IaC Practice Question
This DOP-C02 practice question tests your understanding of configuration management and iac. 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.
A DevOps engineer creates the IAM policy above for an instance role. The role is attached to an EC2 instance that runs an application. The application starts and stops EC2 instances and reads a database password from Systems Manager Parameter Store. However, the application fails to retrieve the parameter. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The parameter is a SecureString and the policy does not grant 'kms:Decrypt' permission for the KMS key.
The policy allows 'ssm:GetParameter' and 'ssm:GetParameters' on the specific parameter ARN. However, to retrieve a parameter, the action 'ssm:GetParameter' is sufficient, but the resource ARN must be correct. The given ARN includes the parameter name '/MyApp/DBPassword'. If the application is using a different path or the parameter is encrypted, the policy might be insufficient. But the most common issue is that the parameter is a SecureString and the policy also needs 'kms:Decrypt' access to the KMS key. Option C is correct because the policy does not include KMS permissions. Option A and B are less likely. Option D is incorrect because the actions are allowed.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The policy does not allow 'ssm:GetParameterHistory'.
Why it's wrong here
GetParameterHistory is not required to retrieve the current parameter value.
✗
The policy does not allow 'ec2:DescribeParameters'.
Why it's wrong here
There is no such action as ec2:DescribeParameters.
✓
The parameter is a SecureString and the policy does not grant 'kms:Decrypt' permission for the KMS key.
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The policy does not allow 'ssm:GetParameter' on the specific resource.
Why it's wrong here
The policy explicitly allows GetParameter on the resource ARN.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DOP-C02 NAT questions on configuration and troubleshooting.
Configuration Management and IaC — This question tests Configuration Management and IaC — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The parameter is a SecureString and the policy does not grant 'kms:Decrypt' permission for the KMS key. — The policy allows 'ssm:GetParameter' and 'ssm:GetParameters' on the specific parameter ARN. However, to retrieve a parameter, the action 'ssm:GetParameter' is sufficient, but the resource ARN must be correct. The given ARN includes the parameter name '/MyApp/DBPassword'. If the application is using a different path or the parameter is encrypted, the policy might be insufficient. But the most common issue is that the parameter is a SecureString and the policy also needs 'kms:Decrypt' access to the KMS key. Option C is correct because the policy does not include KMS permissions. Option A and B are less likely. Option D is incorrect because the actions are allowed.
What should I do if I get this DOP-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DOP-C02 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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