Raising Exceptions from Lambda to API Gateway Caller

You can send exception feedback from a Lambda to an API Gateway API either by raising a Python exception and handling it via a mapping template, or return a specific set of values from the main handler function.

Returning from the Handler Function#

You can return a dictionary that includes at least:

• the desired status code
• the message body (JSONified)
• and whether or not the body is base64 encoded

return {  
    "statusCode": 404,  
    "body": simplejson.dumps(  
        f"User {username} not found"  
    ),  
    "isBase64Encoded": False,  
}

Raising an Exceptions#

Using a mapping template allows you to simply use regex to associate an error message from a plain Python exception with a certain HTTP code. I don’t have any examples because I haven’t done it, preferring the previous method.