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

I have a similar use case (needing to use CloudFormation to manage a lambda function to be used @edge in CloudFront, for which a specific lambda function version is always required, not $LATEST) and my searches landed me at this question first, but after a bit more digging I was happy to find there is now native support for automatic lambda versioning with the new AutoPublishAlias feature of the AWS Serverless Application Model (basically an optional extra set of higher-level constructs for your CloudFormation templates).

Announced here: https://github.com/awslabs/serverless-application-model/issues/41#issuecomment-347723981

For details see:

• https://github.com/awslabs/serverless-application-model/blob/master/docs/safe_lambda_deployments.rst#instant-traffic-shifting-using-lambda-aliases
• https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md#referencing-lambda-version--alias-resources

Essentially you include AutoPublishAlias in your AWS::Serverless::Function definition:

MyFunction:
  Type: "AWS::Serverless::Function"
  Properties:
    # ...
    AutoPublishAlias: MyAlias

And then elsewhere in the CloudFormation template you can reference the latest published version as !Ref MyFunction.Version (yaml syntax).

AWS::Lambda::Version is not useful. You have to add a new resource for every Lambda version. If you want to publish a new version for every Cloudformation update, you have to hack the system.

I solved this issue creating a Lambda backed custom resource which is triggered for every deployment. Inside this Lambda, I am creating a new version for the Lambda function given in parameter.

For the Lambda's source you can check http://serverless-arch-eu-west-1.s3.amazonaws.com/serverless.zip

Here is the example Cloudformation using this Deployment Lambda function (You might need some modification):

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Parameters": {
    "DeploymentTime": {
      "Type": "String",
      "Description": "It is a timestamp value which shows the deployment time. Used to rotate sources."
    }
  },
  "Resources": {
    "LambdaFunctionToBeVersioned": {
      "Type": "AWS::Lambda::Function",
       ## HERE DEFINE YOUR LAMBDA AS USUAL ##
    },
    "DeploymentLambdaRole": {
      "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/AWSLambdaVPCAccessExecutionRole"
        ],
        "Policies": [
          {
            "PolicyName": "LambdaExecutionPolicy",
            "PolicyDocument": {
              "Version": "2012-10-17",
              "Statement": [
                {
                  "Effect": "Allow",
                  "Action": [
                    "lambda:PublishVersion"
                  ],
                  "Resource": [
                    "*"
                  ]
                }
              ]
            }
          }
        ]
      }
    },
    "DeploymentLambda": {
      "Type": "AWS::Lambda::Function",
      "Properties": {
        "Role": {
          "Fn::GetAtt": [
            "DeploymentLambdaRole",
            "Arn"
          ]
        },
        "Handler": "serverless.handler",
        "Runtime": "nodejs4.3",
        "Code": {
          "S3Bucket": {
            "Fn::Sub": "serverless-arch-${AWS::Region}"
          },
          "S3Key": "serverless.zip"
        }
      }
    },
    "LambdaVersion": {
      "Type": "Custom::LambdaVersion",
      "Properties": {
        "ServiceToken": {
          "Fn::GetAtt": [
            "DeploymentLambda",
            "Arn"
          ]
        },
        "FunctionName": {
          "Ref": "LambdaFunctionToBeVersioned"
        },
        "DeploymentTime": {
          "Ref": "DeploymentTime"
        }
      }
    }
  }
}

(Disclaimer: This code is a part of my book, for more information about Lambda & API Gateway you can check: https://www.amazon.com/Building-Serverless-Architectures-Cagatay-Gurturk/dp/1787129195)