Resolve EC2 Health Check Failures with Auto Scaling and CloudWatch Alarms
Which TWO actions should be taken to ensure a highly available and resilient architecture for a critical web application on AWS? (Choose two.)
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 to maintain a desired number of instances.
Correct: B and E. Option B ensures that the desired number of EC2 instances is maintained, providing automatic scaling and fault tolerance. Option E deploys the application across multiple Availability Zones, which protects against an AZ failure. Option A (CloudFront) enhances content delivery but does not directly ensure high availability of the web application. Option C (Multi-AZ RDS with read replicas) improves read performance and provides disaster recovery, but write availability depends on the primary instance. Option D (backups in a different region) is for disaster recovery, not for immediate availability.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Enable Amazon CloudFront with multiple origins.
Why it's wrong here
CloudFront is a global content delivery network that accelerates static and dynamic content through edge caching, but it does not track the health of application instances or initiate automatic instance replacement. Although you can configure multiple origins and failover between them, that failover only occurs in response to HTTP error codes, not underlying compute or AZ failures, so it cannot guarantee the session-level availability required for this architecture.
- ✓
Use an Auto Scaling group to maintain a desired number of instances.
Why this is correct
An Auto Scaling group with a desired capacity continuously monitors instance health via EC2 status checks and optionally Elastic Load Balancing health checks, automatically terminating and relaunching failed instances. By spreading the ASG across multiple Availability Zones and setting the desired count, you ensure that if an instance or an entire AZ fails, replacement capacity is launched to maintain the required number of instances, making this a core high-availability mechanism.
- ✗
Use a Multi-AZ RDS deployment with read replicas.
Why it's wrong here
Multi-AZ RDS automatically provisions a synchronous standby replica in another AZ and provides a failover that promotes the standby, but read replicas are separate, asynchronous copies used to offload read traffic. Read replicas do not support automatic write failover; if the primary fails, you must manually promote a read replica, which is a disruptive manual process rather than a high-availability feature. Confusing these two features commonly leads to incorrectly assuming read replicas deliver HA for writes.
- ✗
Store backups in a different AWS Region.
Why it's wrong here
Storing backups in a different AWS Region is a disaster recovery measure, not a high availability mechanism, because recovery requires restoring databases, reconfiguring DNS, and provisioning infrastructure, all of which take significant time. High availability generally means zero or near-zero downtime with automatic failover, whereas backups are for surviving a regional catastrophe and do not protect against transient failures or provide continuous service during an outage.
- ✓
Deploy the application across multiple Availability Zones.
Why this is correct
Deploying the application across multiple Availability Zones eliminates the single point of failure of a single data center by placing compute, storage, and database resources in physically separate facilities that are designed to fail independently. When paired with load balancing and Auto Scaling, this architecture can continue serving traffic even if an entire AZ becomes unavailable, which is a fundamental pillar of high availability on AWS.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DOP-C02 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 DOP-C02 exam.