This DBS-C01 practice question tests your understanding of management and operations. 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 uses Amazon RDS for MySQL with Multi-AZ deployment. The primary instance fails and the database administrator notices that the failover did not happen automatically. 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.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
The DB instance is in a public subnet.
Why wrong: Public subnet does not affect Multi-AZ failover.
Enhanced Monitoring is disabled.
Why wrong: Enhanced Monitoring provides metrics, not failover.
The standby instance is in a different VPC.
Why wrong: Multi-AZ requires same VPC.
The DB instance is configured as a read replica.
Read replicas do not have automatic failover.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The DB instance is configured as a read replica.
Option A is incorrect because Multi-AZ handles failover automatically. Option B is correct because read replicas do not support automatic failover. Option C is incorrect because it would not prevent failover. Option D is incorrect because monitoring does not affect failover.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
The DB instance is in a public subnet.
Why it's wrong here
Public subnet does not affect Multi-AZ failover.
Enhanced Monitoring is disabled.
Why it's wrong here
Enhanced Monitoring provides metrics, not failover.
The standby instance is in a different VPC.
Why it's wrong here
Multi-AZ requires same VPC.
The DB instance is configured as a read replica.
Why this is correct
Read replicas do not have automatic failover.
Clue confirmation
The clue words "most likely", "primary" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
Common exam traps
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DBS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Management and Operations — This question tests Management and Operations — CIDR notation defines the prefix length..
The correct answer is: The DB instance is configured as a read replica. — Option A is incorrect because Multi-AZ handles failover automatically. Option B is correct because read replicas do not support automatic failover. Option C is incorrect because it would not prevent failover. Option D is incorrect because monitoring does not affect failover.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DBS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Yes — watch for: "most likely", "primary". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
CIDR notation defines the prefix length.
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Last reviewed: Jun 20, 2026
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.
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