How to invoke lambda async with AWS ApiGateway HttpApi

user_1237550 0
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I'm using the new HTTP Api (The one introduced in December 2019) of AWS Api Gateway.

I used to work with REST Api, which lets you trigger lambda functions async by adding X-Amz-Invocation-Type:Event header.

The new HTTP Api does not let you specify that header, how can I call lambda functions asynchronously?

thanks in advance

aws-api-gateway aws-lambda amazon-web-services asynchronous
2 Answers

You can invoke a Lambda function asynchronously via API Gateway only if the integration is non-proxy. By default, HTTP APIs are designed to support only proxy integrations for Lambda and HTTP endpoints so it is not possible to set the X-Amz-Invocation-Type header in the API Gateway integration config.

In order to invoke a Lambda asynchronously via HTTP API, you can use two Lambda functions with one acting as proxy to your actual function.

HTTP API --> Invoke Lambda1 synchronously --> Invoke Lambda2 asynchronously

Below is a sample NodeJS code snippet for Lambda1 to invoke Lambda2 asynchronously -

const params = {
        FunctionName: 'FUNCTION_NAME',
        InvocationType: 'Event',
        Payload: JSON.parse(event.body) // this is the event coming from API Gateway to Lambda1
    };
await lambda.invoke(params).promise(); // await here is only going to wait for the HTTP request to be successful. Once Lambda2 is invoked, it will return immediately
user_59328660

You can invoke a Lambda asynchronously with additional header Integration Request in API Gateway configuration:

For all invocations

Integration Request header in API Gateway

X-Amz-Invocation-Type : Event

To make a decision during the client call

  1. Client's request header

    InvocationType: Event or InvocationType: RequestResponse

  2. Integration Request header in API Gateway

    X-Amz-Invocation-Type header with a mapping expression of method.request.header.InvocationType.

AWS Documentation: Set up asynchronous invocation of the backend Lambda function

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