A company has a two-tier web application. The front-end web servers run on Amazon EC2 instances in a public subnet. The back-end application servers process jobs that are submitted by the front end. The company wants to decouple the front-end and back-end tiers so that the back-end servers can process jobs as they are submitted, even if the front-end servers experience a spike in traffic. The solution must be durable and fully managed, and must allow the front-end servers to send job requests without waiting for the back-end servers to be available. Which AWS service should the company use to send the job requests from the front end to the back end?

Amazon Simple Notification Service (SNS)

Amazon SNS is a pub/sub messaging service used to send notifications to a large number of subscribers (e.g., email, SMS, HTTP endpoints). While SNS can be used to trigger asynchronous processing, it is not designed for buffering job requests between specific front-end and back-end components. SNS pushes messages to all subscribers, and if a subscriber is unavailable, the message may be lost (unless a dead-letter queue is configured). SQS is the better choice for durable, decoupled job queues.

Amazon Kinesis Data Streams

Amazon Kinesis Data Streams is designed for real-time streaming of large amounts of data, such as clickstreams, IoT telemetry, or log data. It is not intended for simple job queueing between application tiers. Kinesis is more complex to set up and manage than SQS for this use case, and it is optimized for high-throughput, ordered data processing, not for decoupling one-to-one job submissions.

AWS Step Functions

AWS Step Functions is a serverless orchestration service that lets you coordinate multiple AWS services into a workflow. It is used to define state machines that sequence tasks, add branching logic, and handle errors. While Step Functions can call SQS, it is not itself a queue. It does not store messages durably for later processing by a fleet of workers; rather, it directly invokes services. For simple decoupling of front-end and back-end, SQS is the appropriate choice.

What does this CLF-C02 question test?

CIDR notation defines the prefix length.

What is the correct answer to this question?

The correct answer is: Amazon Simple Queue Service (SQS) — Amazon Simple Queue Service (SQS) is a fully managed message queuing service that enables you to decouple and scale microservices, distributed systems, and serverless applications. SQS eliminates the complexity and overhead associated with managing and operating message oriented middleware, and empowers developers to focus on differentiating work. Using SQS, the front-end servers can send job requests as messages to a queue, and the back-end servers can poll and process those messages at their own pace. This decouples the two tiers, improves fault tolerance (if a back-end server fails, messages remain in the queue), and allows the system to handle traffic spikes because the queue acts as a buffer.

What should I do if I get this CLF-C02 question wrong?

Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.