Bug: invocation-type: Event is not supported. RequestResponse is only supported.

[ijtarano]

Description:

It seems like Event in boto3 invoke method doesn't work with SAM Local even when boto3 accept this parameter (https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/lambda/client/invoke.html)

Steps to reproduce:

import boto3
import json 

payload = {
}

lambda_client = boto3.client("lambda", endpoint_url="http://localhost:3001", region_name="eu-west-1")
lambda_function_name = "Lambda"

payload_json = json.dumps(payload)

response = lambda_client.invoke(
    InvocationType="Event", # This Event fails
    FunctionName=lambda_function_name,
    Payload=payload_json
)

Observed result:

ClientError: An error occurred (NotImplemented) when calling the Invoke operation: invocation-type: Event is not supported. RequestResponse is only supported.

Additional environment details (Ex: Windows, Mac, Amazon Linux etc)

1. Amazon Linux:
2. sam --version: SAM CLI, version 1.113.0
3. AWS region: eu-west-1

{
  "version": "1.113.0",
  "system": {
    "python": "3.11.3",
    "os": "Linux-4.14.320-243.544.amzn2.x86_64-x86_64-with-glibc2.26"
  },
  "additional_dependencies": {
    "docker_engine": "20.10.23",
    "aws_cdk": "Not available",
    "terraform": "1.7.2"
  },
  "available_beta_feature_env_vars": [
    "SAM_CLI_BETA_FEATURES",
    "SAM_CLI_BETA_BUILD_PERFORMANCE",
    "SAM_CLI_BETA_TERRAFORM_SUPPORT",
    "SAM_CLI_BETA_RUST_CARGO_LAMBDA"
  ]
}

[lucashuy]

Thanks for opening this issue, just to understand the context here, are you running sam local start-lambda and then passing the endpoint to your script here?

[ijtarano]

Yes, of course, It works perfectly with "RequestResponse" InvocationType parameter ;)

[lucashuy]

Thanks for letting us know, this is something that we guard against since async execution isn't something that is currently implemented. I can tag this issue to a feature request instead.

As an alternative, it's possible to use our sam sync --watch command to deploy to AWS and update code live, similar to how one would use sam local start-lambda. This could be a workaround for now.

[ericbambach-qwickrate]

Bump - this feature is a use-case for us and we want to test async events locally. As a workaround we use RequestResponse but its not ideal.

[Danny-Smart]

I also have this use case and for me, neither using "RequestResponse" nor sam sync --watch is a valid workaround.

Searching through issues, I can see that this has been a problem since at least 2019 (#510 (comment)) and has had at least one attempt at a solution closed off (#749)

Please can someone implement this feature?

[ericbambach-qwickrate]

For all those watching, I did workaround this issue by instead of making an async call, my original lambda calls fork() to a tiny process which is responsible for calling invoke() on the function which is intended to be asynchronous. Done properly, the fork() lets the original process continue on while the invoked() lambda runs in the background detached from the original one.

TLDR: I used fork() to hand-code async behavior.