This SCS-C02 practice question tests your understanding of infrastructure security. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 is using AWS WAF to protect its Application Load Balancer (ALB). The security team wants to block requests that do not contain a valid API key in the HTTP header 'X-API-Key'. Which WAF rule type should be used?
String match condition
Why wrong: Does not support regex patterns.
Regex pattern set
Can define a pattern for valid API keys and block invalid ones.
Rate-based rule
Why wrong: Used for rate limiting requests.
IP set
Why wrong: Used for IP-based allow/block lists.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Regex pattern set
A regex pattern set rule is the correct choice because it allows you to define a regular expression pattern that matches the expected format of valid API keys in the 'X-API-Key' header. AWS WAF regex pattern sets can be used in a rule to inspect the header value and block requests that do not match the pattern, providing flexible and precise validation beyond simple string matching.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
String match condition
Why it's wrong here
Does not support regex patterns.
Regex pattern set
Why this is correct
Can define a pattern for valid API keys and block invalid ones.
Related concept
Read the scenario before looking for a memorised answer.
Rate-based rule
Why it's wrong here
Used for rate limiting requests.
IP set
Why it's wrong here
Used for IP-based allow/block lists.
Common exam traps
The trap here is that candidates often confuse string match conditions with regex pattern sets, assuming that a simple 'contains' or 'starts with' string match is sufficient for validating structured data like API keys, when in fact regex provides the necessary pattern flexibility.
Detailed technical explanation
Under the hood, AWS WAF regex pattern sets are compiled into a deterministic finite automaton (DFA) for efficient matching against incoming requests. This allows you to define patterns like '^[A-Za-z0-9]{32}$' to match a 32-character alphanumeric API key, and the rule can be configured to block requests where the header does not match the pattern. In a real-world scenario, this is critical for APIs where keys follow a specific format (e.g., base64-encoded or UUID-based) and simple string matching would be insufficient to reject malformed or spoofed keys.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
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FAQ
Infrastructure Security — This question tests Infrastructure Security — Read the scenario before looking for a memorised answer..
The correct answer is: Regex pattern set — A regex pattern set rule is the correct choice because it allows you to define a regular expression pattern that matches the expected format of valid API keys in the 'X-API-Key' header. AWS WAF regex pattern sets can be used in a rule to inspect the header value and block requests that do not match the pattern, providing flexible and precise validation beyond simple string matching.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This SCS-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 SCS-C02 exam.
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