- A
Create an AMI of the current instance, configure an Auto Scaling group with a launch template that uses the AMI, and attach the existing EBS volume to new instances.
Why wrong: EBS volumes are AZ-specific; an EBS volume attached to an instance in one AZ cannot be attached to an instance in another AZ. This approach does not survive an AZ failure.
- B
Create a multi-AZ Auto Scaling group and use sticky sessions (session affinity) on the ALB to tie users to specific instances.
Why wrong: Sticky sessions ensure a user is directed to the same instance, but if that instance fails, session data in memory is lost. It does not address AZ failure.
- C
Use an Auto Scaling group across multiple AZs, migrate session storage to Amazon ElastiCache (multi-AZ), and migrate application data from EBS to Amazon EFS (file system mounted across AZs).
ElastiCache provides a shared, cross-AZ in-memory session store. EFS provides a shared, cross-AZ file system. The Auto Scaling group launches instances in multiple AZs, and the ALB distributes traffic. This architecture survives an AZ failure.
- D
Use an Auto Scaling group in a single AZ and use a Multi-AZ RDS instance for data storage.
Why wrong: A single AZ Auto Scaling group cannot tolerate an AZ failure. Multi-AZ RDS helps with data redundancy but not compute availability.
SOA-C02 Reliability and Business Continuity Practice Question
This SOA-C02 practice question tests your understanding of reliability and business continuity. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 a single Amazon EC2 instance. The application stores session state in memory and writes critical data to an Amazon EBS volume. The SysOps administrator needs to implement a highly available architecture that can tolerate an Availability Zone (AZ) failure. The administrator plans to use an Auto Scaling group and an Application Load Balancer (ALB). Which combination of steps is required to make the application highly available while preserving session and data durability across AZ failures?
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
Use an Auto Scaling group across multiple AZs, migrate session storage to Amazon ElastiCache (multi-AZ), and migrate application data from EBS to Amazon EFS (file system mounted across AZs).
Option C is correct because it addresses both session state and data durability across AZ failures. Migrating session storage to ElastiCache (multi-AZ) ensures session data survives instance failure, and migrating application data from EBS to EFS provides a shared, multi-AZ file system that persists independently of any single EC2 instance. This combination allows the Auto Scaling group to launch new instances in any AZ and immediately access both session and application data.
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.
- ✗
Create an AMI of the current instance, configure an Auto Scaling group with a launch template that uses the AMI, and attach the existing EBS volume to new instances.
Why it's wrong here
EBS volumes are AZ-specific; an EBS volume attached to an instance in one AZ cannot be attached to an instance in another AZ. This approach does not survive an AZ failure.
- ✗
Create a multi-AZ Auto Scaling group and use sticky sessions (session affinity) on the ALB to tie users to specific instances.
Why it's wrong here
Sticky sessions ensure a user is directed to the same instance, but if that instance fails, session data in memory is lost. It does not address AZ failure.
- ✓
Use an Auto Scaling group across multiple AZs, migrate session storage to Amazon ElastiCache (multi-AZ), and migrate application data from EBS to Amazon EFS (file system mounted across AZs).
Why this is correct
ElastiCache provides a shared, cross-AZ in-memory session store. EFS provides a shared, cross-AZ file system. The Auto Scaling group launches instances in multiple AZs, and the ALB distributes traffic. This architecture survives an AZ failure.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use an Auto Scaling group in a single AZ and use a Multi-AZ RDS instance for data storage.
Why it's wrong here
A single AZ Auto Scaling group cannot tolerate an AZ failure. Multi-AZ RDS helps with data redundancy but not compute availability.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume sticky sessions (session affinity) alone are sufficient for high availability, but they fail to realize that sticky sessions do not replicate session state across instances, so an instance failure still loses the session data.
Detailed technical explanation
How to think about this question
ElastiCache for Redis with Multi-AZ automatically replicates data across AZs and provides automatic failover, ensuring session data is available even if an entire AZ fails. Amazon EFS is a regional, NFSv4-based file system that can be mounted concurrently by instances in multiple AZs, providing shared access to application data without the single-AZ limitation of EBS. Under the hood, EFS uses a distributed data storage layer across multiple AZs within a region, achieving 99.999999999% durability.
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.
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Reliability and Business Continuity — study guide chapter
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FAQ
Questions learners often ask
What does this SOA-C02 question test?
Reliability and Business Continuity — This question tests Reliability and Business Continuity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use an Auto Scaling group across multiple AZs, migrate session storage to Amazon ElastiCache (multi-AZ), and migrate application data from EBS to Amazon EFS (file system mounted across AZs). — Option C is correct because it addresses both session state and data durability across AZ failures. Migrating session storage to ElastiCache (multi-AZ) ensures session data survives instance failure, and migrating application data from EBS to EFS provides a shared, multi-AZ file system that persists independently of any single EC2 instance. This combination allows the Auto Scaling group to launch new instances in any AZ and immediately access both session and application data.
What should I do if I get this SOA-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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