SAA-C03 Design Cost-Optimized Architectures Practice Question
Exhibit
Architecture inventory: 3 EC2 instances for RabbitMQ 2 EC2 instances for application workers Average broker CPU: 8%-12% Average broker memory: 18%-22% Monthly ops time spent on broker patching, backups, and failover testing: 14 hours Message requirements: Durable queueing At-least-once delivery acceptable No need for broker-managed topics or complex routing Failure note: A node reboot caused a 9-minute enqueue outage last month
Based on the exhibit, the company runs a self-managed RabbitMQ cluster on EC2 for asynchronous work. The queue only needs durable at-least-once delivery, and the application does not require AMQP-specific features such as exchanges, routing keys, or broker plugins. Which change is the best cost-optimization move?
⚠ Common exam trap
A common mix-up: candidates assume Amazon MQ for RabbitMQ is always the cheapest managed option, but SQS is more cost-effective when AMQP-specific features are not required, as it eliminates per-instance costs and leverages a serverless pricing model.
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
✓
Replace RabbitMQ with Amazon SQS Standard and keep the workers unchanged except for the queue client library.
Amazon SQS Standard provides at-least-once delivery and durable message storage without requiring AMQP-specific features like exchanges or routing keys. Replacing RabbitMQ with SQS eliminates the operational overhead of managing EC2 instances and RabbitMQ clusters, while SQS's pay-per-request pricing is more cost-effective than running EC2 instances 24/7 for a self-managed queue.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Replace RabbitMQ with Amazon SQS Standard and keep the workers unchanged except for the queue client library.
Why this is correct
Amazon SQS is a fully managed queue that satisfies durable, at-least-once messaging without requiring broker administration. It removes the EC2 broker fleet, patching, backups, and failover testing, and it reduces outage risk from broker maintenance. Because the workload does not need AMQP-specific features such as exchanges or routing keys, SQS is the most cost-effective and operationally simple replacement.
- ✗
Replace RabbitMQ with Amazon MQ for RabbitMQ to keep the same protocol and reduce costs.
Why it's wrong here
Replacing RabbitMQ with Amazon MQ for RabbitMQ preserves the AMQP protocol but introduces a managed service cost premium over a self-managed EC2 cluster, failing to reduce expenditure when the application requires only durable at-least-once delivery without AMQP-specific features. This option tempts because Amazon MQ handles broker maintenance and scaling, which would be cost-effective if the workload demanded complex routing or plugins that EC2 management overhead made expensive.
- ✗
Increase the RabbitMQ instance size and add a fourth node for higher availability.
Why it's wrong here
The exhibit shows very low CPU and memory utilization, so scaling the cluster up would raise cost without addressing the underlying self-managed broker overhead. It also does not eliminate the patching, backup, and failover-testing burden.
- ✗
Move the queue to Amazon DynamoDB and use scans for consumers to detect new messages.
Why it's wrong here
DynamoDB is a serverless key-value database, not a messaging service; using table scans to poll for messages is a classic anti-pattern. Scanning is expensive and inefficient because it reads every item in the table, consuming read capacity units and costing more as the queue grows. Moreover, DynamoDB does not natively provide queue semantics like visibility timeouts, redrive policies, or delayed delivery, so you would have to build and maintain those features yourself, which increases complexity and operational burden.
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