How to create a new version of a Lambda function using CloudFormation?

Question

I\'m trying to create a new version of a Lambda function using CloudFormation.

I want to have multiple versions of the same Lambda function so that I can (a) point a

Answer 1

Looking for a similar thing that works with Lambda functions deployed from S3.

My use case was this:

• You have a cloudformation template that creates a Lambda function from an S3 bucket location
• You need to update this function so you make code changes locally and push the changes to S3
• You now want to push these changes to Lambda so you try to update the stack and cloudformation says there are no changes to update so you have to resort to manually updating the code using the AWS Lambda console.

Not happy with this I looked for an alternative and came across this question. None of the answers exactly worked for me so I have taken some ideas and adapted the answers here and made my own version written in Python.

This code is adapted from the answer from @wjordan so credit to him for the idea and the original answer. The differences are:

• This is written in Python
• It works with Lambda code deployed from an S3 bucket
• It updates the code and publishes a new version

You need a nonce parameter. You change the value of this parameter when the code needs to be republished to Lambda. This is to ensure that cloudformation will update your custom resource. When the custom resource is updated, it will run the Python code that ultimately updates your Lambda code.

Hope this helps someone.

Description: Publish a new version of a Lambda function whenever the code is updated.
Parameters:
  Nonce:
    Description: Change this string when code is updated.
    Type: String
    Default: "Test"
Resources:
  MyCustomResource:
    Type: Custom::Resource
    Properties:
      ServiceToken: !GetAtt MyFunction.Arn
      Nonce: !Ref Nonce
  MyFunction:
    Type: AWS::Lambda::Function
    Properties:
      Handler: index.handler
      Role: !GetAtt LambdaExecutionRole.Arn
      Code:
        S3Bucket: BucketContainingYourLambdaFunction
        S3Key: KeyToYourLambdaFunction.zip
      Runtime: "python3.6"
  LambdaExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
        - Effect: Allow
          Principal: {Service: [lambda.amazonaws.com]}
          Action: ['sts:AssumeRole']
      Path: /
      ManagedPolicyArns:
      - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
  LambdaDeployCustomResource:
    Type: Custom::LambdaVersion
    Properties:
      ServiceToken: !GetAtt LambdaDeployFunction.Arn
      FunctionName: !Ref MyFunction
      S3Bucket: BucketContainingYourLambdaFunction
      S3Key: KeyToYourLambdaFunction.zip
      Nonce: !Ref Nonce
  LambdaDeployFunction:
    Type: AWS::Lambda::Function
    DependsOn: LambdaDeployFunctionExecutionRole
    Properties:
      Handler: "index.handler"
      Role: !GetAtt LambdaDeployFunctionExecutionRole.Arn
      Code:
        ZipFile: !Sub |
          import boto3
          import json
          import logging
          import cfnresponse
          import time
          from botocore.exceptions import ClientError

          def handler(event, context):
            logger = logging.getLogger()
            logger.setLevel(logging.INFO)
            logger.info (f"Input parameters from cloud formation: {event}")
            responseData = {}
            if (event["RequestType"] == 'Delete'):
              logger.info("Responding to delete event...")
              cfnresponse.send(event, context, cfnresponse.SUCCESS, responseData)

            try:            
              lambdaClient = boto3.client('lambda')
              s3Bucket = event['ResourceProperties']['S3Bucket']
              s3Key = event['ResourceProperties']['S3Key']
              functionName = event['ResourceProperties']['FunctionName']
              logger.info("Updating the function code for Lambda function '{}' to use the code stored in S3 bucket '{}' at key location '{}'".format(functionName, s3Bucket, s3Key))
              logger.info("Sleeping for 5 seconds to allow IAM permisisons to take effect")
              time.sleep(5)             
              response = lambdaClient.update_function_code(
                FunctionName=functionName,
                S3Bucket='{}'.format(s3Bucket),
                S3Key='{}'.format(s3Key),
                Publish=True)
              responseValue = "Function: {}, Version: {}, Last Modified: {}".format(response["FunctionName"],response["Version"],response["LastModified"])
              responseData['Data'] = responseValue
              cfnresponse.send(event, context, cfnresponse.SUCCESS, responseData, response["FunctionArn"])
            except ClientError as e:
              errorMessage = e.response['Error']['Message']
              logger.error(errorMessage)
              cfnresponse.send(event, context, cfnresponse.FAILED, responseData)
      Runtime: "python3.6"
      Timeout: "30"
  LambdaDeployFunctionExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
        - Effect: Allow
          Principal: 
            Service: lambda.amazonaws.com
          Action: 
            - sts:AssumeRole
      Path: /
      ManagedPolicyArns:
      - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
      Policies:
      - PolicyName: ReadS3BucketContainingLambdaCode
        PolicyDocument:
          Version: 2012-10-17
          Statement:
          - Effect: Allow
            Action: 
              - s3:GetObject              
            Resource: ArnOfS3BucketContainingLambdaCode/*
      - PolicyName: UpdateCodeAndPublishVersion
        PolicyDocument:
          Version: 2012-10-17
          Statement:
          - Effect: Allow
            Action: 
              - lambda:UpdateFunctionCode
              - lambda:PublishVersion
            Resource: '*'
Outputs:
  LambdaVersion:
    Value: !GetAtt LambdaDeploy.Version
  CustomResourceResult:
    Value: !GetAtt MyCustomResource.Result