Question 121 of 505

Application Deployment and Security →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the database pod being repeatedly killed by OOMKilled due to exceeding its 512Mi memory limit causes intermittent connection refused errors. When Kubernetes terminates the pod for out-of-memory, the backend service’s connection attempts to the ClusterIP service fail because no ready database pod exists during the restart window. This scenario tests your understanding of how resource limits interact with pod lifecycle and service discovery in Kubernetes, a key concept for the Cisco DevNet Associate 200-901 exam. A common trap is blaming the liveness or readiness probes, but the probes only detect unavailability—they don’t cause the restarts. Instead, focus on the OOMKilled event in pod logs as the root cause. Memory tip: “OOM kills the pod, probes just watch the clock”—the limit is the trigger, not the probe.

200-901 Application Deployment and Security Practice Question

This 200-901 practice question tests your understanding of application deployment and security. 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 runs a microservices application on a Kubernetes cluster with 10 worker nodes. The application consists of 3 services: frontend, backend, and database. The database service is stateful and uses persistent volumes. Recently, the operations team noticed that the backend service is experiencing intermittent failures with 'Connection refused' errors when trying to connect to the database. The database service is exposed via a ClusterIP service named 'database-service'. The backend service uses environment variable DB_HOST=database-service to connect. The pod logs show that the connection is attempted to an IP address that does not correspond to any database pod. Further investigation reveals that the database pod has been restarted multiple times due to OOMKilled errors. The backend service is configured with a liveness probe that checks the health endpoint every 10 seconds, and a readiness probe that checks the same endpoint every 5 seconds. The database pod has resource limits set to 512Mi memory and 500m CPU. The node running the database pod has 4Gi memory and 2 CPU cores. What is the most likely cause of the intermittent connection failures?

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.

Question 1hardmultiple choice

Full question →

A
The backend service is using a hardcoded IP address instead of the service DNS name.
Why wrong: The stem states the backend uses DB_HOST=database-service, so it uses DNS, not a hardcoded IP.
B
The backend service's readiness probe is failing, so it is not receiving traffic, but the backend still tries to connect.
Why wrong: If the backend readiness probe fails, the backend pod would be removed from service endpoints, but the error is on the backend trying to connect to the database, not the backend itself.
C
The database pod is being killed due to memory limits, causing frequent restarts and temporary unavailability; the backend's connection attempts fail during the restart window.
The OOMKilled errors indicate the database pod exceeds memory limits. When it restarts, there is a brief period of unavailability, causing 'Connection refused' errors.
D
The DNS entry for database-service is cached and pointing to the old pod IP after the database pod restarts.
Why wrong: ClusterIP services use a virtual IP that does not change; pod restarts do not affect the ClusterIP. DNS caching is not the issue.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The database pod is being killed due to memory limits, causing frequent restarts and temporary unavailability; the backend's connection attempts fail during the restart window.

The intermittent 'Connection refused' errors are caused by the database pod being repeatedly killed due to exceeding its memory limit (512Mi), which triggers OOMKilled restarts. During the restart window, the database pod is unavailable, and the backend's connection attempts to the ClusterIP service (which resolves to the pod's IP) fail because no pod is ready to accept connections. The frequent restarts create a pattern of temporary unavailability that aligns with the observed symptoms.

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 backend service is using a hardcoded IP address instead of the service DNS name.
Why it's wrong here
The stem states the backend uses DB_HOST=database-service, so it uses DNS, not a hardcoded IP.
✗
The backend service's readiness probe is failing, so it is not receiving traffic, but the backend still tries to connect.
Why it's wrong here
If the backend readiness probe fails, the backend pod would be removed from service endpoints, but the error is on the backend trying to connect to the database, not the backend itself.
✓
The database pod is being killed due to memory limits, causing frequent restarts and temporary unavailability; the backend's connection attempts fail during the restart window.
Why this is correct
The OOMKilled errors indicate the database pod exceeds memory limits. When it restarts, there is a brief period of unavailability, causing 'Connection refused' errors.
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 DNS entry for database-service is cached and pointing to the old pod IP after the database pod restarts.
Why it's wrong here
ClusterIP services use a virtual IP that does not change; pod restarts do not affect the ClusterIP. DNS caching is not the issue.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the distinction between pod-level failures (like OOMKilled causing restarts) and service-level issues (like DNS caching or readiness probes), leading candidates to incorrectly attribute the problem to DNS or probe misconfiguration instead of the resource constraint causing the database pod to be temporarily unavailable.

Detailed technical explanation

How to think about this question

When a pod is OOMKilled, Kubernetes restarts it, but during the container startup (including init containers and application initialization), the pod is not ready to accept traffic. The ClusterIP service uses iptables or IPVS rules to forward traffic to the pod's IP, but if the pod is not running, the connection is refused at the transport layer (TCP RST). The backend's connection attempt to the service's ClusterIP results in a direct connection to the pod's IP via kube-proxy, and if that pod is down, the kernel returns 'Connection refused' immediately, not a timeout.

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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.

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.

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FAQ

Questions learners often ask

What does this 200-901 question test?

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 database pod is being killed due to memory limits, causing frequent restarts and temporary unavailability; the backend's connection attempts fail during the restart window. — The intermittent 'Connection refused' errors are caused by the database pod being repeatedly killed due to exceeding its memory limit (512Mi), which triggers OOMKilled restarts. During the restart window, the database pod is unavailable, and the backend's connection attempts to the ClusterIP service (which resolves to the pod's IP) fail because no pod is ready to accept connections. The frequent restarts create a pattern of temporary unavailability that aligns with the observed symptoms.

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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