200-901 Application Deployment and Security Practice Question
This 200-901 practice question tests your understanding of application deployment and security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 microservices application deployed on Kubernetes. There are three services: frontend, backend, and database. The frontend is exposed via an Ingress. The API gateway is used for authentication. Recently, after updating the backend service, users are experiencing 401 Unauthorized errors when accessing endpoints that previously worked. The authentication mechanism uses JWT tokens issued by an external identity provider. The JWT tokens are validated by the API gateway. The backend service itself does not validate tokens; it relies on the gateway to forward user identity via headers. The development team checked the logs and found that the backend is receiving requests with the correct JWT from the gateway but still returning 401. 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 backend service code now attempts to validate the JWT itself and fails.
The scenario states that the backend service relies on the gateway to forward user identity via headers and does not validate JWT tokens itself. If the new backend version now attempts to validate the JWT, it would likely fail because the backend lacks the necessary signing key or validation logic, causing 401 errors even though the gateway correctly forwards the token. This matches option D, as the change in backend behavior introduces a new validation step that was not present before.
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 Ingress controller is stripping the Authorization header before forwarding to the backend.
Why it's wrong here
Logs show backend receives the correct JWT, so header is present.
✗
The API gateway's JWT signing key has changed and the backend is using the old key.
Why it's wrong here
If the key changed, the gateway would fail to validate tokens, not the backend.
✗
The new backend version uses a different HTTP method for the affected endpoints.
Why it's wrong here
Method mismatch would cause 405 or similar, not 401.
✓
The backend service code now attempts to validate the JWT itself and fails.
Why this is correct
Likely the update added token validation code that is not properly configured.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that JWT validation must happen at the backend, but here the trap is that the backend was never supposed to validate tokens, and a code change introducing such validation causes the 401 errors, not a problem with the gateway or Ingress.
Trap categories for this question
Similar concept trap
Method mismatch would cause 405 or similar, not 401.
Command / output trap
Logs show backend receives the correct JWT, so header is present.
Detailed technical explanation
How to think about this question
In microservices architectures with an API gateway, the gateway typically validates JWT tokens and then forwards user identity (e.g., user ID, roles) via HTTP headers like X-User-Id or X-User-Roles. If a backend service is updated to directly validate the JWT, it must have access to the same signing key (e.g., RS256 public key) and validation logic; otherwise, token validation fails, resulting in 401 errors. This is a common pitfall when teams refactor authentication without coordinating with the gateway's trust model.
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 junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
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.
Application Deployment and Security — This question tests Application Deployment and Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The backend service code now attempts to validate the JWT itself and fails. — The scenario states that the backend service relies on the gateway to forward user identity via headers and does not validate JWT tokens itself. If the new backend version now attempts to validate the JWT, it would likely fail because the backend lacks the necessary signing key or validation logic, causing 401 errors even though the gateway correctly forwards the token. This matches option D, as the change in backend behavior introduces a new validation step that was not present before.
What should I do if I get this 200-901 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.
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Question Discussion
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