SOA-C02 Reliability and Business Continuity Practice Question
A company has an AWS Lambda function that processes S3 events. The function is critical and must be available even if one Availability Zone fails. How can a SysOps administrator ensure high availability for the Lambda function?
⚠ Common exam trap
Many exam-takers confuse the need to configure VPC subnets for Lambda functions with the Lambda service's inherent AZ resilience, leading them to incorrectly select Option C, which is only relevant for VPC-attached functions accessing private resources, not for the function's own availability.
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
✓
No action is required; Lambda functions are inherently highly available within a region.
AWS Lambda functions are inherently highly available within an AWS Region. The Lambda service automatically runs your function across multiple Availability Zones (AZs) to handle failures of individual AZs. No additional configuration is required to achieve AZ-level resilience; the service manages the underlying compute fleet and network infrastructure to ensure continued operation even if one AZ fails.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use an Application Load Balancer to distribute events to multiple Lambda functions.
Why it's wrong here
An Application Load Balancer operates at Layer 7 for HTTP/HTTPS traffic, but S3 event notifications do not invoke Lambda through a network endpoint; they trigger the function asynchronously via an internal event source mapping. Lambda already runs across multiple Availability Zones within a region, and the service automatically scales concurrency based on incoming S3 event volume. Attaching an ALB would not increase availability—it would introduce an unnecessary regional component and a different invocation model that does not apply to S3 event processing.
- ✓
No action is required; Lambda functions are inherently highly available within a region.
Why this is correct
No configuration is required because AWS Lambda is a regional, highly available service that executes function code in multiple Availability Zones automatically. When an S3 event triggers a Lambda function asynchronously, the event is queued and the Lambda service manages capacity, scaling, and redundant infrastructure to ensure the invocation can be processed successfully. The function is also covered by the Lambda service SLA, and the S3 event notification mechanism is designed to be reliable within the same region. Therefore, taking no action is the correct and sufficient approach.
- ✗
Configure the Lambda function to run in two subnets in different Availability Zones.
Why it's wrong here
Lambda functions are not tied to subnets unless you explicitly run them inside a VPC, and even then the configuration is for accessing private resources—not for adding availability. If you do enable VPC, you must specify subnets, and the Lambda service automatically places execution environments across the Availability Zones represented by those subnets; manually selecting two subnets does not increase resilience beyond that default. For an S3-triggered function that only processes object events, VPC connectivity is usually unnecessary, and adding subnet configuration could even complicate internet access or require a NAT gateway.
- ✗
Deploy the Lambda function in two separate regions and use Route 53 failover.
Why it's wrong here
Deploying the Lambda function to two regions with Route 53 failover is unnecessary and misapplied for S3 event processing, because S3 event notifications are regional and do not "fail over" to another region on their own—you would need cross-region replication and a separate event source mapping in each destination bucket. Lambda itself is already highly available within its region, so a second region only adds cost, latency, and operational complexity without improving the single-region reliability of the function. Route 53 DNS failover is designed for HTTP/TCP endpoints, not for asynchronous event triggers.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SOA-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 SOA-C02 exam.