Using crhelper with moto

[RajasGujarathi]

I have a Lambda function that is implemented to be invoked as Cloudformation Custom resources. The Lambda function uses crhelper for interaction with Cloudformation.

Is it possible to test such a Lambda by invoking, using moto?

[bblommers]

Hi @RajasGujarathi, only the MotoServer supports custom resources, and only when using cfnresponse (https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/cfn-lambda-function-code-cfnresponsemodule.html).
So crhelper is not implemented (yet).

If you have a small example test to show what you're trying to accomplish, I'm happy to have a look to see if that's doable in Moto - just no promises when I'll have time 🙂

[RajasGujarathi]

Yes, we are using MotoServer.

If you have a small example test to show what you're trying to accomplish

Please find the below snippet 👇

1. requirements.txt

crhelper==2.0.11
requests==2.32.3

2. lambda_function.py

import logging
import json
from crhelper import CfnResource

logging.getLogger().setLevel(logging.INFO)

HELPER = CfnResource(json_logging=False, log_level='DEBUG', boto_level='CRITICAL')

@HELPER.create
def create(event, _):

    logging.info("Received create event" )
   .
   .
   .
    return {
        'statusCode': 200,
        'body': json.dumps("Received create event")
    }

@HELPER.update
def update(event, _):
    
    logging.info("Received update event" )
   .
   .
   .
    return {
        'statusCode': 200,
        'body': json.dumps("Received update event")
    }
        
@HELPER.delete
def delete(event, _):

    logging.info("Received delete event" )
   .
   .
   .
    return {
        'statusCode': 200,
        'body': json.dumps("Received delete event")
    }

def lambda_handler(event, context):
    logging.info(event)
    try:
        HELPER(event, context)
    except Exception as error:
        HELPER.init_failure(error)

This Lambda is then invoked via AWS CloudFormation Custom Resource. In one of the use cases, the Create/Update/Delete logic deals with interacting with ssm.

We want to test this Lambda code by invoking it in the test environment.

Let me know if you need additional information

[bblommers]

I assumed that crhelper would be provided by AWS, but that's not the case. I've just tried a simple CF stack, and the logs give me an import error:

Runtime.ImportModuleError: Unable to import module 'index': No module named 'crhelper'

How do you package the crhelper module so that it's available in the lambda @RajasGujarathi?

For reference, the template I used:

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Description": "Sample template using Custom Resource",
  "Resources": {
    "CustomInfo": {
      "Type": "Custom::Info",
      "Properties": {
        "ServiceToken": {
          "Fn::GetAtt": [
            "InfoFunction",
            "Arn"
          ]
        },
        "Region": {
          "Ref": "AWS::Region"
        },
        "MyProperty": "stuff"
      }
    },
    "InfoFunction": {
      "Type": "AWS::Lambda::Function",
      "Properties": {
        "Code": {
          "ZipFile": {
            "Fn::Join": [
              "\n",
              [
                "",
                "import logging",
                "import json",
                "from crhelper import CfnResource",
                "",
                "logging.getLogger().setLevel(logging.INFO)",
                "",
                "HELPER = CfnResource(json_logging=False, log_level='DEBUG', boto_level='CRITICAL')",
                "",
                "@HELPER.create",
                "def create(event, _):",
                "",
                "    logging.info('Received create event' )",
                "    return {",
                "        \"statusCode\": 200,",
                "        \"body\": json.dumps('Received create event')",
                "    }",
                "",
                "@HELPER.update",
                "def update(event, _):",
                "    ",
                "    logging.info('Received update event' )",
                "    return {",
                "        \"statusCode\": 200,",
                "        \"body\": json.dumps('Received update event')",
                "    }",
                "        ",
                "@HELPER.delete",
                "def delete(event, _):",
                "",
                "    logging.info('Received delete event' )",
                "    return {",
                "        \"statusCode\": 200,",
                "        \"body\": json.dumps('Received delete event')",
                "    }",
                "",
                "def lambda_handler(event, context):",
                "    logging.info(event)",
                "    try:",
                "        HELPER(event, context)",
                "    except Exception as error:",
                "        HELPER.init_failure(error)"
              ]
            ]
          }
        },
        "Handler": "index.lambda_handler",
        "Role": {
          "Fn::GetAtt": [
            "LambdaExecutionRole",
            "Arn"
          ]
        },
        "Runtime": "python3.8",
        "Timeout": "30"
      }
    },
    "LambdaExecutionRole": {
      "Type": "AWS::IAM::Role",
      "Properties": {
        "AssumeRolePolicyDocument": {
          "Version": "2012-10-17",
          "Statement": [
            {
              "Effect": "Allow",
              "Principal": {
                "Service": [
                  "lambda.amazonaws.com"
                ]
              },
              "Action": [
                "sts:AssumeRole"
              ]
            }
          ]
        },
        "Path": "/",
        "Policies": [
          {
            "PolicyName": "root",
            "PolicyDocument": {
              "Version": "2012-10-17",
              "Statement": [
                {
                  "Effect": "Allow",
                  "Action": [
                    "logs:CreateLogGroup",
                    "logs:CreateLogStream",
                    "logs:PutLogEvents"
                  ],
                  "Resource": "arn:aws:logs:*:*:*"
                }
              ]
            }
          }
        ]
      }
    }
  },
  "Outputs": {
    "infokey": {
      "Description": "A very important value",
      "Value": {
        "Fn::GetAtt": [
          "CustomInfo",
          "info_value"
        ]
      }
    }
  }
}

[RajasGujarathi]

We have a custom build framework, which does the build for Lambda.

But in essence, it sees if a folder (Lambda code directory) has a requirement.txt file. If it finds one, it creates a temporary folder and copies the content of the folder, then does a pip install -r requirements.txt, and finally, zip the complete temporary folder (now the temporary folder contains code + dependencies) and push the zip it to S3.

[bblommers]

Ah, I understand. It looks like crhelper works essentially the same as cfnresponse, so if crhelper is packaged with the code, I see no reason why it wouldn't work. Are you running into any specific problems?

[RajasGujarathi]

I did not get the opportunity to draft a proper reply. I am currently on vacation, will get back on this as soon as I return.