DBS-C01 Monitoring and Troubleshooting Practice Question
A company is running a MongoDB-compatible Amazon DocumentDB cluster. The application team reports that write operations are failing intermittently with a `WriteConcernError` indicating that the write concern could not be satisfied. The cluster has one primary and two replicas. What is the MOST likely cause of this issue?
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
✓
One of the replicas is down or experiencing high replication lag
The WriteConcernError occurs because the write concern requires acknowledgment from a certain number of replicas. With a cluster of one primary and two replicas, if any replica is down or has high replication lag, the write concern requirement cannot be satisfied. Option A is correct because that is the most likely cause. Option B is incorrect because the cluster has enough replicas for majority write concern if all are healthy. Option C is incorrect because read preference does not affect write operations. Option D is incorrect because the primary being overloaded with reads would not cause a WriteConcernError; it would affect performance but not the ability to satisfy write concern.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
One of the replicas is down or experiencing high replication lag
Why this is correct
If a replica is down, the write concern 'majority' cannot be satisfied because only the primary and one replica are available, but majority may require two replicas depending on configuration.
- ✗
The cluster does not have enough replica instances to satisfy the write concern
Why it's wrong here
With 3 nodes, a majority write concern requires 2 nodes, which is possible if all are healthy.
- ✗
The application is using an incorrect read preference
Why it's wrong here
Read preference affects reads, not writes.
- ✗
The primary instance is overloaded with read requests
Why it's wrong here
Read load does not affect write concern.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DBS-C01 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 DBS-C01 exam.