Amazon API Gateway
Developer Guide

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Set up Asynchronous Invocation of the Backend Lambda Function

In Lambda non-proxy (custom) integration, the backend Lambda function is invoked synchronously by default. This is the desired behavior for most REST API operations. Some applications, however, require work to be performed asynchronously (as a batch operation or a long-latency operation), typically by a separate backend component. In this case, the backend Lambda function is invoked asynchronously, and the front-end REST API method doesn't return the result.

You can configure the Lambda function for a Lambda non-proxy integration to be invoked asynchronously by specifying 'Event' as the Lambda invocation type. This is done as follows:

Configure Lambda asynchronous invocation in the API Gateway console

  1. In Integration Request, add an X-Amz-Invocation-Type header.

  2. In Method Request, add an InvocationType header and map it to the X-Amz-Invocation-Type header in the Integration Request with either a static value of 'Event' or the header mapping expression of method.request.header.InvocationType. For the latter, the client must include the InvocationType:Event header when making a request to the API method.