Step-by-Step Breakdown:

Requirement Summary:

AWS AppSync API needs toinvoke Lambda functions

Some Lambda functions arelong-running

AppSync shouldreturn immediately, minimizingoperational overhead

**Option A: AppSync + Lambda as data source usingEvent Mode

✅Correct: AWS AppSync supportsasynchronous (event) invocationof Lambda data sources usingEvent Mode.

Event Mode means:

AppSync invokes Lambdaasynchronously

Immediately returns aresponseto the client (typically a predefined payload or null)

Ideal forfire-and-forgetworkloads or when the response is not immediately needed

Option B: Increase Lambda timeout

❌Incorrect: This keeps AppSync waiting.

Even with increased timeout, synchronous invocations wouldblock AppSync responses.

Option C: SQS queue + polling Lambda

❌Possible but too complex for this use case.

Requires additional infrastructure: queue + mapping + custom logic.

Higheroperational overheadcompared to built-in AppSync Event Mode.

Option D: Enable caching in AppSync

❌Irrelevant: AppSync cache is for optimizing repeated read queries,not for async workflows.

Asynchronous Lambda with AppSync:https://docs.aws.amazon.com/appsync/latest/devguide/resolver-mapping-template-reference-lambda.html#async-lambda-invocation

Lambda as AppSync Data Source:https://docs.aws.amazon.com/appsync/latest/devguide/tutorial-lambda-resolvers.html

Event Mode Docs:https://docs.aws.amazon.com/appsync/latest/devguide/lambda-resolvers.html#event-invocation-mode