Last updated: 2022-08-26

To configure a REST API to pass data to a backend Lambda function, use a Lambda custom integration.

To pass query string parameters to an HTTP endpoint, use an HTTP custom integration.

Important: Make sure that the input data is supplied as the integration request payload. It’s a best practice to use a mapping template to supply the payload. For more information, see Map request and response payloads between method and integration.

1.    Open the Lambda console.

2.    Choose Create function . The Create function page opens with the Author from scratch option selected.

3.    In the Basic information pane, do the following: For Function name , enter a name that describes your function's purpose. For example: MapTemplate . For Runtime , choose Python 3.9 .

4.    For Permissions , expand Change default execution role .

5.    Choose Use an existing role . A dropdown list of existing roles appears.

6.    For Existing role , choose the Lambda execution role that you created earlier.

7.    Choose Create function .

8.    From the Code tab, in Code source , replace the code in lambda_function.py with the following:

import json

def lambda_handler(event, context):
    print(event)
    return {
        'statusCode': 200,
        'body': json.dumps(event) # returning the data sent to backend lambda function as API response.
    }

9.    Choose Deploy .

For more information, see Building Lambda functions with Python.

1.    Open the API Gateway console.

2.    Choose Create API .

-or-

(If this is your first time using API Gateway) A page that introduces you to the features of the service appears. In REST API , choose Build . When the Create Example API popup appears, choose OK .

3.    For Choose an API type , in the REST API pane, choose Build .

4.    In Create new API , choose New API .

5.    In Settings , do the following: For API name , enter a name that describes your API's purpose. For example: MappingTemplateTutorial . (Optional) For Description , enter a short description your API's purpose. For example, Send Data to Backend Lambda function/HTTP endpoint . For Endpoint Type , choose Regional .

6.    Choose Create API .

1.    In the API Gateway console, choose the name of the API that you created in the previous step. Your API's Resources page opens.

2.    On the Resources page, choose Actions . Then, choose Create Resource .

3.    In the New Child Resource pane, for Configure as proxy resource , select the check mark icon , and then choose Create Resource .

4.    On the /{proxy+} - ANY - Setup page, do the following:

• For Integration type , choose Lambda Function Proxy .
• For Lambda Region , choose the AWS Region that hosts your function.
• For Lambda Function , enter the function's name MappingTemplateTutorial .

Choose Save . An Add Permission to Lambda Function popup appears, choose OK .

7.    On the / {proxy+} - ANY - Method Execution page, choose Integration Request .

8.    On the / {proxy+} - ANY - Integration Request page, do the following:

• Uncheck the Use Lambda Proxy integration icon box. A Switch to Lambda integration popup appears.
• In the popup, choose OK. An Add Permission to Lambda Function popup appears. In the popup, choose OK
• Expand Mapping Templates .
• For Request body passthrough , choose When there are no templates defined (recommended) .

Choose Add mapping template . For Content-Type , enter application/json . Then, choose the check mark icon.

9.    Choose the Generate template dropdown list, and then choose Method Request passthrough .

10.    In the mapping template editor, enter the following:

##  See http://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-mapping-template-reference.html
#set($allParams = $input.params())
{
"method" : "$context.httpMethod", ## API method
"authcontext" : "$context.authorizer.stringkey", ## Optional output from Lambda Authorizers
## passthrough body
"body-json" : $input.json('$'),
## passthrough headers, querystrings and path parameters
"params" : {
#foreach($type in $allParams.keySet())
    #set($params = $allParams.get($type))
"$type" : {
    #foreach($paramName in $params.keySet())
    "$paramName" : "$util.escapeJavaScript($params.get($paramName))"
        #if($foreach.hasNext),#end
    #end
}
    #if($foreach.hasNext),#end
#end
}
}

11.    Choose Save .

12.    Choose Method Execution to come back to / {proxy+} - ANY - Method Execution page.

13.    Choose Method Response to setup valid method response.

14.    On /{proxy+} - ANY - Method Response page, Choose Add Response .

15.    For HTTP status code, enter 200 . Then, choose the check mark icon.

16.    Choose Actions to Deploy API to a stage.

1.    Follow the instructions in Deploy a REST API to a stage. For more information, see Setting up a stage using the API Gateway console.

2.    In the Stage Editor pane, copy the Invoke URL to your clipboard.

REST API Invoke URL example

https://1a2bc3d456.execute-api.us-east-1.amazonaws.com/stage

To confirm that all data is being passed to backend Lambda function or HTTP endpoint by your API, run the following curl command:

Important: Replace https://restApiId.execute-api.region.amazonaws.com/stageName with your API's invoke URL.

curl -i --location --request POST 'https://1a2bc3d456.execute-api.us-east-1.amazonaws.com/stage/path1/path2?query1=querystring1&query2=querystring2' --header 'header1: value1' --header 'header2: value2' --header 'Content-Type: application/json' --data-raw '{"keybody":"valuebody"}'

The command output includes all data received by the backend Lambda function to the client. You can update the output message for your environment.

Note: To install curl on Windows, see Downloads on the Git website. For more information about curl, see the curl project website.