Question:
I have an AWS lambda function which I can call synchronously and get results back alright with below code
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response = lambda_client.invoke( FunctionName=FUNCTION_NAME, InvocationType='RequestResponse', LogType='Tail', Payload=payload, Qualifier=$LATEST ) |
The response Payload is of type <botocore.response.StreamingBody object at 0x115fb3160> So I use below code to extract the payload which works fine.
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response_body = response['Payload'] response_str = response_body.read().decode('utf-8') response_dict = eval(response_str) |
Now, I need to call my lambda asynchronously, so I change the invocation type with InvocationType='Event'
It gives me a response with payload of the same type as before, botocore.response.StreamingBody object but I am getting error with this line – response_dict = eval(response_str)
The error message says
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response_dict = eval(response_str) File " ^ SyntaxError: unexpected EOF while parsing |
What am I missing? If the response payload is same type as synchronous call, why is this parsing error? Any suggestion?
EDIT
For clarity, I understand that if the InvocationType='Event', then we only get the status of the invoke call, not the lambda function result. In my case though, I need both – launch the lambda async and get the result back when done. How do I do that? Is writing the result back to s3 and periodically checking that the only option?
Answer:
InvocationType='Event' means you aren’t getting a response. An asynchronous Lambda invocation means you just want to invoke the function, not wait for the response. The response payload from the function is discarded by the service.
When you invoke a function asynchronously, Lambda sends the event to a queue. A separate process reads events from the queue and runs your function. When the event is added to the queue, Lambda returns a success response without additional information. (emphasis added)
https://docs.aws.amazon.com/lambda/latest/dg/invocation-async.html
Note that the queue mentioned here is a queue inside the Lambda service, not to be confused with Amazon Simple Queue Service (SQS).