Build a secure serverless API on AWS

Architecture flow

1. Authenticate: Cognito signs users in and issues tokens.
2. Authorize and route: API Gateway validates the token and accepts an API request.
3. Run logic: API Gateway invokes a Lambda function with a scoped execution role.
4. Persist data: The function reads or writes DynamoDB through authorized API calls.

Text alternative: A client authenticates with Amazon Cognito, sends its token to Amazon API Gateway, which invokes AWS Lambda; the function reads and writes Amazon DynamoDB.

How the services connect

Authentication and application data flow are separate: Cognito issues a token to the client, while API Gateway validates that token before invoking backend logic.

Lambda should receive only the context it needs and use a least-privilege IAM execution role for DynamoDB. Partition-key design, conditional writes, and idempotency remain application responsibilities.

Add throttling, structured logs, alarms, and WAF protection according to exposure. Serverless removes server management, but service quotas, concurrency, retry behavior, and per-request cost still need design.

Tradeoffs and caveats

• Scales each tier independently and avoids idle server capacity.
• Distributed logs, quotas, and retry semantics make end-to-end debugging more deliberate.
• Synchronous API limits are a poor fit for long-running jobs; move those to an asynchronous workflow.

AWS services in this pattern

• Amazon Cognito — User auth & identity
• Amazon API Gateway — Managed APIs
• AWS Lambda — Run code without servers
• Amazon DynamoDB — Serverless NoSQL

Primary AWS sources

• AWS serverless multi-tier web application
• Creating event-driven architectures with Lambda