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200-901 Practice Question: A company runs a microservices application on a…
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?
⚠ Common exam trap
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.
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.
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.
- ✗
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-901 practice question is part of Courseiva's free Cisco 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 200-901 exam.