The answer is that the ElastiCache cluster is not configured for Multi-AZ, and a node failure caused all sessions to be lost. This is correct because a stateful web application using ElastiCache Redis for session storage loses all cached data when a single node fails in a non-Multi-AZ setup, as there is no replica to fail over to. The scaling event itself does not directly affect ElastiCache, but it often coincides with increased load that can trigger node failures, exposing the lack of redundancy. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this question tests your understanding that ElastiCache Multi-AZ is essential for session persistence, not just high availability—a common trap is confusing scaling events with data loss mechanisms. Remember the mnemonic: “No replica, no recovery—Multi-AZ keeps sessions alive.”
DOP-C02 Resilient Cloud Solutions Practice Question
This DOP-C02 practice question tests your understanding of resilient cloud solutions. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 stateful web application on EC2 instances in an Auto Scaling group. The application uses an Application Load Balancer (ALB) and an Amazon ElastiCache Redis cluster. Users report that after a scaling event, they are logged out and lose session data. 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 ElastiCache cluster is not configured for Multi-AZ and a node failure caused all sessions to be lost
Option D is correct because the scenario describes a stateful web application that relies on ElastiCache Redis for session storage. If the ElastiCache cluster is not configured for Multi-AZ, a node failure can cause all cached session data to be lost, logging users out. This is the most likely cause of session loss after a scaling event, as scaling events do not directly affect ElastiCache data persistence.
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 ALB health check interval is too short, causing healthy instances to be marked unhealthy
Why it's wrong here
Health checks do not cause session loss.
✗
The ElastiCache cluster is configured with in-transit encryption, causing session tokens to be invalidated
Why it's wrong here
Encryption does not invalidate sessions.
✗
The Auto Scaling group is using a termination policy that terminates the oldest instance first, which holds active sessions
Why it's wrong here
Even if oldest instance terminated, sessions stored in ElastiCache should survive.
✓
The ElastiCache cluster is not configured for Multi-AZ and a node failure caused all sessions to be lost
Why this is correct
Without Multi-AZ, a node failure can cause data loss.
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
The trap here is that candidates may focus on the Auto Scaling group's termination policy or ALB health checks, overlooking that the session data is stored externally in ElastiCache and that its lack of high availability is the root cause of session loss.
Detailed technical explanation
How to think about this question
ElastiCache Redis stores session data in memory, and without Multi-AZ, a single node failure results in complete data loss because Redis by default does not persist to disk (unless configured with append-only file or snapshot). In a production environment, Multi-AZ with automatic failover ensures that a replica in another Availability Zone takes over with the same data, preventing session loss during node failures or scaling events. The Auto Scaling group's scaling event itself does not affect ElastiCache, but if the Redis cluster fails concurrently, sessions are lost.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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.
Resilient Cloud Solutions — This question tests Resilient Cloud Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The ElastiCache cluster is not configured for Multi-AZ and a node failure caused all sessions to be lost — Option D is correct because the scenario describes a stateful web application that relies on ElastiCache Redis for session storage. If the ElastiCache cluster is not configured for Multi-AZ, a node failure can cause all cached session data to be lost, logging users out. This is the most likely cause of session loss after a scaling event, as scaling events do not directly affect ElastiCache data persistence.
What should I do if I get this DOP-C02 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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