Improving Availability with ALB and EC2
Which TWO actions can be taken to improve the availability of a web application hosted on EC2 instances behind an Application Load Balancer? (Select two.)
Quick Answer
The correct actions to improve availability are deploying EC2 instances across multiple Availability Zones and using an Auto Scaling group to replace unhealthy instances. Distributing instances across multiple Availability Zones eliminates a single point of failure by ensuring that if one zone goes down, the Application Load Balancer can route traffic to healthy instances in another zone. An Auto Scaling group automatically replaces failed or unhealthy instances, maintaining the desired capacity and further enhancing fault tolerance. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this question tests your understanding of high-availability architecture patterns, often with traps like choosing a single subnet or a larger instance type—both of which improve performance or simplicity, not availability. A common memory tip is to remember that availability comes from redundancy across zones and automated recovery, not from bigger or fewer resources. Think “spread and replace” to recall the two key actions.
⚠ Common exam trap
The trap is equating 'more capacity' (larger instances, more instances in one AZ) with 'higher availability,' when availability requires distributing across failure domains and automating recovery.
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
✓
Configure an Auto Scaling group with health checks to replace unhealthy instances.
Option A is correct because an Auto Scaling group configured with health checks (ELB or EC2 health checks) automatically detects and replaces unhealthy instances, maintaining the desired capacity and thus improving availability. Option C is correct because deploying EC2 instances across multiple Availability Zones provides fault isolation; if one AZ fails, the Application Load Balancer routes traffic to healthy instances in other AZs, maintaining availability. Option B is incorrect because larger instance types increase capacity/performance but do not address redundancy or failure recovery. Option D is incorrect because using a single Region does not improve availability against AZ-level failures and is not a redundancy measure. Option E is incorrect because placing all instances in a single subnet concentrates them in one AZ, reducing availability and creating a single point of failure.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Configure an Auto Scaling group with health checks to replace unhealthy instances.
Why this is correct
An Auto Scaling group with ELB health checks detects instances failing load balancer health checks and terminates then replaces them automatically, restoring capacity without manual intervention. This directly addresses instance-level failure, one axis of the availability requirement.
- ✗
Use larger EC2 instance types.
Why it's wrong here
Larger instance types increase per-instance capacity but leave a single point of failure, so they do not improve availability. They are tempting because sizing up reduces overload, and this would be the right action for performance or throughput problems rather than resilience.
- ✓
Deploy the EC2 instances across multiple Availability Zones.
Why this is correct
Spreading EC2 instances across multiple Availability Zones ensures that an AZ-level outage, such as a power or network failure, only removes part of the fleet. The Application Load Balancer routes to the surviving AZs, satisfying the availability requirement.
- ✗
Use a single AWS Region for all instances.
Why it's wrong here
Concentrating all instances in one Region means a Regional outage takes down the whole application, reducing rather than improving availability. It is tempting because single-Region deployment lowers latency and data-transfer cost, and it would be correct when latency or cost outweighs multi-Region resilience.
- ✗
Place all EC2 instances in a single subnet.
Why it's wrong here
A single subnet spans one Availability Zone, so an AZ failure removes every instance and the load balancer cannot route around it. It is tempting because one subnet simplifies networking, and it would be correct for non-production workloads where cost and simplicity matter more than resilience.
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Same concept, more angles
2 more ways this is tested on SOA-C02
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which TWO actions can a SysOps administrator take to improve the availability of a web application using an Application Load Balancer (ALB) and EC2 instances? (Choose two.)
medium- A.Place all instances in a single subnet to reduce latency
- ✓ B.Configure health checks on the target group
- ✓ C.Deploy EC2 instances in multiple Availability Zones
- D.Use larger instance types to handle more traffic
- E.Increase the deregistration delay (connection draining) timeout
Why B: Health checks allow the ALB to automatically detect unhealthy EC2 instances and stop routing traffic to them, which prevents failed requests from reaching users. By configuring health checks on the target group, the ALB can mark instances as unhealthy based on criteria like HTTP response codes or timeout thresholds, and then route traffic only to healthy instances. This directly improves availability by ensuring that requests are not sent to failed or degraded instances.
Variation 2. Which TWO actions should a SysOps administrator take to improve the availability and reduce latency for a web application hosted on EC2 instances behind an Application Load Balancer?
medium- A.Use larger EC2 instance types to handle more traffic.
- B.Configure the ALB health check to have a shorter interval.
- C.Use an Amazon CloudFront distribution in front of the ALB to cache content at edge locations.
- ✓ D.Implement Auto Scaling to add instances based on CPU utilization.
- ✓ E.Deploy EC2 instances in multiple Availability Zones.
Why D: Auto Scaling based on CPU utilization dynamically adjusts the number of EC2 instances to match demand, improving availability by ensuring sufficient capacity during traffic spikes and reducing latency by distributing load across more instances. Option E is correct because deploying EC2 instances in multiple Availability Zones (AZs) provides fault tolerance: if one AZ fails, the ALB continues routing traffic to healthy instances in other AZs, which also reduces latency by serving users from the closest AZ.
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
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