The correct next step is to check if the API requires an API key or other authentication that the canary is not providing. A 403 Forbidden error on a publicly accessible endpoint typically means the request reached the server but was rejected due to missing or invalid credentials, not due to network or permission issues. In AWS, API Gateway often enforces usage plans or API key requirements, and a CloudWatch Synthetics canary must include the appropriate x-api-key header or authentication token in its script. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your ability to distinguish between IAM permissions (which govern AWS actions) and application-layer authentication (which governs API access). A common trap is to immediately check VPC settings or logging, but a 403 on a public endpoint points to missing credentials, not connectivity. Memory tip: 403 means “Forbidden, not Found”—the API sees you, but it doesn’t trust you, so check the key.
DOP-C02 Incident and Event Response Practice Question
This DOP-C02 practice question tests your understanding of incident and event response. 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 uses CloudWatch Synthetics canaries to monitor a critical API endpoint. Recently, a canary started failing with a '403 Forbidden' error. The DevOps engineer verifies that the canary's IAM role has the necessary permissions to invoke the API and that the API endpoint is publicly accessible. What should the engineer check NEXT?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Check if the API requires an API key or other authentication that the canary is not providing.
Option B is correct because the API may have a usage plan or API key requirement, and the canary must include the appropriate key or authentication header. Option A is wrong because the canary's VPC configuration does not affect public endpoints. Option C is wrong because logging is for debugging, not the immediate cause. Option D is wrong because increasing memory won't fix a 403 error.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Review the canary's CloudWatch Logs for any runtime errors.
Why it's wrong here
Logs may show the error but not the root cause; checking authentication is more direct.
✗
Increase the canary's memory to 512 MB to prevent timeout-related issues.
Why it's wrong here
Memory affects execution time, not authorization; the error is specifically 403.
✓
Check if the API requires an API key or other authentication that the canary is not providing.
Why this is correct
A 403 often indicates authorization failure; missing API key is a common cause.
Verify that the canary is attached to the correct VPC and subnet.
Why it's wrong here
For a public endpoint, VPC attachment is unnecessary; the canary runs in a managed VPC by default.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Trap categories for this question
Command / output trap
Logs may show the error but not the root cause; checking authentication is more direct.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DOP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Incident and Event Response — This question tests Incident and Event Response — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Check if the API requires an API key or other authentication that the canary is not providing. — Option B is correct because the API may have a usage plan or API key requirement, and the canary must include the appropriate key or authentication header. Option A is wrong because the canary's VPC configuration does not affect public endpoints. Option C is wrong because logging is for debugging, not the immediate cause. Option D is wrong because increasing memory won't fix a 403 error.
What should I do if I get this DOP-C02 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DOP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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