EC2 Instance Recovery with CloudWatch Alarms

SAA-C03 By islever Editorial Last updated

Design highly available and/or fault-tolerant architectures.

Short answer

C Create an Amazon CloudWatch alarm to recover the EC2 instance in case of failure.

Question

A company is running a legacy system on an Amazon EC2 instance. The application code cannot be modified, and the system cannot run on more than one instance. A solutions architect must design a resilient solution that can improve the recovery time for the system. What should the solutions architect recommend to meet these requirements?
  1. Enable termination protection for the EC2 instance.
  2. Configure the EC2 instance for Multi-AZ deployment.
  3. Create an Amazon CloudWatch alarm to recover the EC2 instance in case of failure. Correct Answer
  4. Launch the EC2 instance with two Amazon Elastic Block Store (Amazon EBS) volumes that use RAID configurations for storage redundancy.

Key Takeaways

The core trap is confusing data redundancy (RAID) with system resilience; RAID protects against disk failure but does not recover a failed operating system or application process, whereas CloudWatch can detect and reboot the instance.

This question evaluates designing highly available architectures for legacy EC2 workloads where code modification is restricted. It establishes that Amazon CloudWatch alarms are the correct mechanism to automate instance recovery when multi-AZ deployment is not an option.

Common mistake: Many learners choose Option D (RAID), mistakenly believing that storage-level redundancy constitutes overall system resiliency. However, RAID cannot recover from host failures, OS crashes, or application hangs, which are common causes of system downtime.

Expert Analysis

Why the Answer Is Correct

Option C is the only viable solution given the constraint that the application cannot run on more than one instance. Amazon CloudWatch allows you to monitor specific metrics (such as CPU utilization or status check failures) and trigger actions via SNS or EventBridge. By configuring an alarm to stop/restart or replace the instance upon failure detection, you significantly improve the Mean Time To Recovery (MTTR). This approach provides automated resilience without requiring architectural changes to the legacy application.

Why the Other Options Are Wrong

Option A (Termination Protection) prevents accidental deletion but offers zero protection against hardware failures, OS crashes, or malicious termination by authorized users. Option B (Multi-AZ) is invalid because AWS does not support running a single EC2 instance across multiple Availability Zones simultaneously; Multi-AZ applies to services like RDS or ELB, or requires active-active/passive setup with load balancers, which violates the "cannot run on more than one instance" constraint. Option D (RAID) addresses disk redundancy, not instance availability. As noted in community feedback, "RAID improves data resilience, but won't recover the instance if the system itself fails." Furthermore, AWS explicitly discourages using RAID with EBS volumes due to performance overhead and lack of managed redundancy.

Community Comment Notes

The community consensus strongly favors Option C, with many users highlighting the critical distinction between data protection and instance recovery. One user noted that "Question about 'improve the recovery time'... it's 100% C," emphasizing that RAID does not solve the recovery time objective for a crashed instance. Another commenter pointed out the limitation of Multi-AZ: "Question says 'cannot run on more than one instance,'" confirming that B is architecturally impossible for this scenario. While some initially considered RAID, the prevailing view is that it fails to address the holistic system failure requirement.

Official Reference

These links open the official vendor documentation in a new tab.

Exam Strategy

When faced with constraints preventing horizontal scaling or multi-AZ deployments, always look for automated recovery mechanisms like CloudWatch Alarms combined with EC2 Actions. Remember that 'resiliency' in the context of a single instance often means rapid detection and restart, not just data backup.

Frequently Asked Questions

Why can't I use Multi-AZ for a single EC2 instance?

AWS EC2 instances are bound to a single Availability Zone. Multi-AZ is supported by managed services like RDS or ElastiCache, not raw EC2 instances. You would need two separate instances and a load balancer to achieve Multi-AZ redundancy.

Does RAID protect against EC2 instance failure?

No. RAID (Redundant Array of Independent Disks) only protects against physical disk failures. If the OS crashes, the application hangs, or the underlying host fails, RAID cannot restore service. CloudWatch alarms are required to detect and recover these states.

More SAA-C03 FAQ →

Community Votes

C
79%
D
21%

79% of anonymous learners picked answer C. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 9 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 9

  1. [Removed] 👍 15 Answered C
    A. Enable termination protection for the EC2 instance. No. Termination protection is about avoid accidentally delete the instance B. Configure the EC2 instance for Multi-AZ deployment. No. Question says "cannot run on more than one instance" C. Create an Amazon CloudWatch alarm to recover the EC2 instance in case of failure. Yes. CloudWatch can be used to recover the instance: https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/UsingAlarmActions.html#AddingRecoverActions D. Launch the EC2 instance with two Amazon Elastic Block Store (Amazon EBS) volumes that use RAID configurations for storage redundancy. No. Raid could be helpful to increase resilience, but does not help with "improve the recovery time"
  2. osmk 👍 6 Answered D
    https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/raid-config.html
  3. mohammadthainat 👍 5 Answered C
    Question about """improve the recovery time for the system""" RAID improves data resilience, but won't recover the instance if the system itself fails. it's 100% C
  4. dkw2342 👍 3
    Pretty sure option D is NOT correct. > RAID 5 and RAID 6 are not recommended for Amazon EBS (...). > RAID 1 is also not recommended for use with Amazon EBS. https://docs.aws.amazon.com/ebs/latest/userguide/raid-config.html#raid-config-options
  5. stephensimudemy 👍 2 Answered C
    Can only run 1 instance. improve recovery time.
Show 4 more comments
  1. haci 👍 1
    For those who choose C, the question asks that "must design a resilient solution".. C may improve recovery time but it has nothing to do with resiliency.
  2. buzzinmumbai 👍 1
    Option should be B .They are not asking about storage anywhere. In muti-AZ you application runs on the primary and the secondary is kept in sync.
  3. stephensimudemy 👍 1
    Option B. Question never ask anything about storage.
  4. Andy_09 👍 8
    Option C

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