AWS Config
Developer Guide

Example AWS Lambda Functions and Events for AWS Config Rules

Each custom Config rule is associated with an AWS Lambda function, which is custom code that contains the evaluation logic for the rule. When the trigger for a Config rule occurs (for example, when AWS Config detects a configuration change), AWS Config invokes the rule's Lambda function by publishing an event, which is a JSON object that provides the configuration data that the function evaluates.

For more information about functions and events in AWS Lambda, see Function and Event Sources in the AWS Lambda Developer Guide.