Which combination of AWS services forms a scalable, event-driven architecture with minimal operational overhead?

• A. AWS Lambda for compute and EventBridge (or SNS/SQS) for events.
• B. Amazon EC2 with SQS and CloudWatch.
• C. AWS Step Functions with Lambda.
• D. AWS Fargate with API Gateway.

Answer: (A)

Event-driven, serverless architectures scale automatically and minimize operations when you pair a serverless compute service with a managed event bus. Using AWS Lambda for compute and EventBridge (or SNS/SQS) for events is the ideal combination here. Lambda runs your code in response to events, scaling up or down automatically with demand and charging only for compute time and invocations. EventBridge provides a scalable, centralized way to route events to many targets, while SNS offers pub/sub messaging and SQS gives durable queues for decoupling producers and consumers. Together, they create a loosely coupled pipeline that handles varying workloads with near-zero operational overhead.

Other options involve managing servers or containers, which introduces more maintenance and capacity planning. EC2 requires patching, scaling groups, and server management; pairing EC2 with SQS and CloudWatch still entails managing infrastructure and capacity. Step Functions with Lambda adds orchestration but isn’t the simplest, most scalable event-routing pattern for a broad, decoupled event-driven workflow. Fargate with API Gateway uses containerized services, which, while serverless to an extent, incurs more operational considerations than a pure Lambda + event bus setup.