The answer is that the trust policy of the role does not include Lambda as a trusted entity. For a Lambda function to assume an IAM role, that role’s trust policy must explicitly grant the Lambda service principal (lambda.amazonaws.com) permission to assume the role via the sts:AssumeRole action. Without this trust relationship, Lambda cannot obtain temporary credentials to perform actions like writing logs, regardless of the permissions attached to the role. On the AWS Certified Security Specialty SCS-C02 exam, this concept tests your understanding of the separation between trust policies (who can assume the role) and permissions policies (what actions the role can perform). A common trap is focusing only on the attached IAM policies or resource-based policies, but the failure here is a missing trust policy entry. Remember the mnemonic: "Trust who, then allow what" — the trust policy controls who can assume the role, while the permissions policy controls what they can do after assuming it.
SCS-C02 Identity and Access Management Practice Question
This SCS-C02 practice question tests your understanding of identity and access management. 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 security team is troubleshooting an issue where an IAM role assumed by a Lambda function is unable to write logs to CloudWatch Logs. The role has an attached policy that allows logs:CreateLogGroup and logs:PutLogEvents. What is a likely reason for the failure?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The trust policy of the role does not include Lambda as a trusted entity.
Lambda execution role must have a trust policy allowing Lambda to assume it. Option A is irrelevant. Option C is about resource policy. Option D is about VPC permissions.
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 trust policy of the role does not include Lambda as a trusted entity.
Why this is correct
Without trust policy, Lambda cannot assume the role.
Related concept
Static NAT maps one inside address to one outside address.
✗
The Lambda function is in a VPC without a NAT gateway.
Why it's wrong here
VPC configuration does not affect CloudWatch Logs access if VPC endpoints are configured.
✗
The role does not have permission to create network interfaces.
Why it's wrong here
That is for VPC networking, not CloudWatch Logs.
✗
The CloudWatch Logs resource policy denies the role.
Why it's wrong here
Resource policy is for cross-account, not same account.
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 SCS-C02 NAT questions on configuration and troubleshooting.
Identity and Access Management — This question tests Identity and Access Management — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The trust policy of the role does not include Lambda as a trusted entity. — Lambda execution role must have a trust policy allowing Lambda to assume it. Option A is irrelevant. Option C is about resource policy. Option D is about VPC permissions.
What should I do if I get this SCS-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 SCS-C02 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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