The answer is that the KMS key policy does not grant the Firehose delivery stream permission to use the key for encryption. This is the most likely cause because, while CloudWatch Logs can successfully send data to Firehose, the delivery stream itself requires explicit `kms:Decrypt` and `kms:GenerateDataKey` permissions on the KMS key to encrypt the data at rest in the OpenSearch cluster and during transit. Without these permissions, Firehose cannot perform server-side encryption, resulting in the `AccessDenied` errors. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of cross-account KMS key policies and the specific IAM permissions needed by AWS services acting as consumers. A common trap is assuming that if the source (CloudWatch Logs) has permissions, the intermediate service (Firehose) inherits them—it does not. Remember the mnemonic: "Firehose needs its own keys to hose the data securely."
SAP-C02 Practice Question: Design Solutions for Organizational Complexity
This SAP-C02 practice question tests your understanding of design solutions for organizational complexity. 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 company has a centralized logging solution using Amazon OpenSearch Service (successor to Amazon Elasticsearch Service) in a central logging account. Application logs from hundreds of EC2 instances across multiple accounts are shipped to the OpenSearch cluster via Amazon Kinesis Data Firehose. The security team requires that all log data be encrypted at rest and in transit. The logging account has a KMS key used to encrypt the OpenSearch cluster and the Firehose delivery stream. Recently, the security team noticed that some log deliveries are failing with 'AccessDenied' errors. The CloudWatch Logs delivery to Firehose is configured correctly. What is the most likely cause of the failure?
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 KMS key policy does not grant the Firehose delivery stream permission to use the key for encryption.
The most likely cause is that the KMS key policy does not grant the Firehose delivery stream permission to use the key for encryption. Even though the CloudWatch Logs subscription filter is correctly configured to send data to Firehose, Firehose must have kms:Decrypt and kms:GenerateDataKey permissions on the KMS key to encrypt the data at rest in the OpenSearch cluster and in transit. Without these permissions, Firehose cannot encrypt the data, resulting in 'AccessDenied' errors.
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.
✗
The CloudWatch Logs subscription filter does not have permissions to write to Firehose.
Why it's wrong here
The subscription filter uses a service-linked role; if it worked before, it's not the issue.
✗
The OpenSearch cluster's access policy denies write access from the Firehose stream.
Why it's wrong here
The error is 'AccessDenied' during delivery, not at the cluster level.
✓
The KMS key policy does not grant the Firehose delivery stream permission to use the key for encryption.
Why this is correct
Firehose needs kms:Encrypt and kms:Decrypt permissions on the key.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The Firehose delivery stream does not have a TLS certificate configured.
Why it's wrong here
TLS is handled by the endpoint, not a certificate on the stream.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume the error is due to network or access policies (Options A or B) rather than recognizing that KMS key policies must explicitly grant encryption permissions to intermediate services like Firehose, which is a subtle but critical requirement for encrypted log pipelines.
Detailed technical explanation
How to think about this question
Amazon Kinesis Data Firehose uses server-side encryption with AWS KMS (SSE-KMS) to encrypt data at rest in the delivery stream and when writing to destinations like OpenSearch. The KMS key policy must explicitly grant the Firehose service principal (firehose.amazonaws.com) and the delivery stream's IAM role permissions for kms:Decrypt and kms:GenerateDataKey. A common misconfiguration is omitting the kms:GenerateDataKey permission, which is required for Firehose to create data encryption keys for each record batch.
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Design Solutions for Organizational Complexity — This question tests Design Solutions for Organizational Complexity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The KMS key policy does not grant the Firehose delivery stream permission to use the key for encryption. — The most likely cause is that the KMS key policy does not grant the Firehose delivery stream permission to use the key for encryption. Even though the CloudWatch Logs subscription filter is correctly configured to send data to Firehose, Firehose must have kms:Decrypt and kms:GenerateDataKey permissions on the KMS key to encrypt the data at rest in the OpenSearch cluster and in transit. Without these permissions, Firehose cannot encrypt the data, resulting in 'AccessDenied' errors.
What should I do if I get this SAP-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This SAP-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SAP-C02 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.