Using AWS CloudFormation to deploy an edge lambda

deploy.sh

#!/bin/sh

aws cloudformation deploy \
  --template-file stack.yaml \
  --stack-name edge-lambda-test \
  --capabilities CAPABILITY_IAM \
  --parameter-overrides Nonce=$RANDOM

stack.yaml

AWSTemplateFormatVersion: '2010-09-09'

Parameters:
  Nonce:
    Type: String

Outputs:
  Host:
    Value: !GetAtt Distribution.DomainName

Resources:
  Bucket:
    Type: AWS::S3::Bucket

  Distribution:
    Type: AWS::CloudFront::Distribution
    Properties:
      DistributionConfig:
        Enabled: true
        Origins:
        - Id: !Ref Bucket
          DomainName: !GetAtt Bucket.DomainName
          S3OriginConfig: {}
        DefaultCacheBehavior:
          TargetOriginId: !Ref Bucket
          ForwardedValues:
            QueryString: true
          ViewerProtocolPolicy: redirect-to-https
          LambdaFunctionAssociations:
          - EventType: viewer-request
            LambdaFunctionARN: !GetAtt IndexLambdaVersion.FunctionArn

  IndexLambda:
    Type: AWS::Lambda::Function
    Properties:
      Role: !GetAtt IndexLambdaRole.Arn
      Runtime: nodejs6.10
      Handler: index.handler
      Code:
        ZipFile: |
          exports.handler = (event, ctx, cb) => {
            const status = '200'
            const headers = {
              'content-type': [{
                key: 'Content-Type',
                value: 'application/json'
              }]
            }
            const body = JSON.stringify(event, null, 2)
            const response = {status, headers, body}

            cb(null, response)
          }

  IndexLambdaRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
        - Effect: Allow
          Principal:
            Service:
            - lambda.amazonaws.com
            - edgelambda.amazonaws.com
          Action: sts:AssumeRole
      ManagedPolicyArns:
      - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole

  IndexLambdaVersion:
    Type: Custom::LatestLambdaVersion
    Properties:
      ServiceToken: !GetAtt PublishLambdaVersion.Arn
      FunctionName: !Ref IndexLambda
      Nonce: !Ref Nonce

  # Custom resource for getting latest version of a lambda,
  # as required by CloudFront.

  PublishLambdaVersion:
    Type: AWS::Lambda::Function
    Properties:
      Handler: index.handler
      Runtime: nodejs6.10
      Role: !GetAtt PublishLambdaVersionRole.Arn
      Code:
        ZipFile: |
          const {Lambda} = require('aws-sdk')
          const {send, SUCCESS, FAILED} = require('cfn-response')
          const lambda = new Lambda()

          exports.handler = (event, context) => {
            const {RequestType, ResourceProperties: {FunctionName}} = event

            if (RequestType == 'Delete') return send(event, context, SUCCESS)

            lambda.publishVersion({FunctionName}, (err, {FunctionArn}) => {
              err
                ? send(event, context, FAILED, err)
                : send(event, context, SUCCESS, {FunctionArn})
            })
          }

  PublishLambdaVersionRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
        - Effect: Allow
          Principal:
            Service: lambda.amazonaws.com
          Action: sts:AssumeRole
      ManagedPolicyArns:
      - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
      Policies:
      - PolicyName: PublishVersion
        PolicyDocument:
          Version: '2012-10-17'
          Statement:
          - Effect: Allow
            Action: lambda:PublishVersion
            Resource: '*'

I was reading through AWS docs.
Seems now we get Lambda Versioning out of the box.
May be this could be modified as follows without using the Cloudformation custom resource and an additional IAM Role.

VersionedIndexLambda:
    Type: 'AWS::Lambda::Version'
    Properties:
        FunctionName: !Ref IndexLambda

Distribution:
    Type: AWS::CloudFront::Distribution
      ......
        ......
          LambdaFunctionAssociations:
             - EventType: viewer-request
               LambdaFunctionARN: !Ref VersionedIndexLambda
 

Anybody tried this way?

@nom3ad I have tried this, I have found that the lambda version does not update when you redeploy your code. Jed has gifted you the solution above.

@LpmRaven Because AWS::Lambda::Version resources can only be created or delete not updated.

So, what you would have to do is create a second version to replace the current version.

First Deploy

VersionedIndexLambdaA:
    Type: 'AWS::Lambda::Version'
    Properties:
        FunctionName: !Ref IndexLambda

Distribution:
    Type: AWS::CloudFront::Distribution
      ......
        ......
          LambdaFunctionAssociations:
             - EventType: viewer-request
               LambdaFunctionARN: !Ref VersionedIndexLambdaA

Second Deploy - Will create a second lambda version now and deploy it to the distribution

VersionedIndexLambdaA:
    Type: 'AWS::Lambda::Version'
    Properties:
        FunctionName: !Ref IndexLambda

VersionedIndexLambdaB:
    Type: 'AWS::Lambda::Version'
    Properties:
        FunctionName: !Ref IndexLambda

Distribution:
    Type: AWS::CloudFront::Distribution
      ......
        ......
          LambdaFunctionAssociations:
             - EventType: viewer-request
               LambdaFunctionARN: !Ref VersionedIndexLambdaB

It has some oddities to it but it could be better than creating a whole other lambda just to deploy another lambda.

@LpmRaven Because AWS::Lambda::Version resources can only be created or delete not updated.

So, what you would have to do is create a second version to replace the current version.

First Deploy

VersionedIndexLambdaA:
    Type: 'AWS::Lambda::Version'
    Properties:
        FunctionName: !Ref IndexLambda

Distribution:
    Type: AWS::CloudFront::Distribution
      ......
        ......
          LambdaFunctionAssociations:
             - EventType: viewer-request
               LambdaFunctionARN: !Ref VersionedIndexLambdaA

Second Deploy - Will create a second lambda version now and deploy it to the distribution

VersionedIndexLambdaA:
    Type: 'AWS::Lambda::Version'
    Properties:
        FunctionName: !Ref IndexLambda

VersionedIndexLambdaB:
    Type: 'AWS::Lambda::Version'
    Properties:
        FunctionName: !Ref IndexLambda

Distribution:
    Type: AWS::CloudFront::Distribution
      ......
        ......
          LambdaFunctionAssociations:
             - EventType: viewer-request
               LambdaFunctionARN: !Ref VersionedIndexLambdaB

It has some oddities to it but it could be better than creating a whole other lambda just to deploy another lambda.

Yes @haydenk, but unfortunately that is not at all practical for continuous deployment. Its much easier to have a lambda just publish a new version every time you make code changes.

So I have taken some of the code here and turned it into a CI/CD pipeline that will update to a new lambda@edge version every time code is released. https://github.com/LpmRaven/lambda-edge-language-region-redirect/tree/master/cloudformation

Hopefully, it will help someone as I had to generate a random nonce in 'buildspec' to force update the version number.

@LpmRaven I agree it's awkward but I wouldn't say it's not practical. The current solution is relying on an outside resource to finish the deployment process after CloudFormation update has been completed. Keeping it in CloudFormation allows you easily to revert to VersionedIndexLambdaA if for some reason VersionedIndexLambdaB has some unintended side effects, for some reason, with another deployment.

Just to re-emphasis, I do admit it is a very awkward solution. Awkward enough to say either solution would be fine, it's just a matter of what you're willing to deal with long term.

@haydenk Take a look at the link I provided in the previous reply. You can revert to a previous lambda version by hardcoding the arn attached to the CloudFront distribution ...and you don't need to change cloudformation every time you update your lambda@edge.

Lambda update problem already solved in AWS SAM - see https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/sam-specification-generated-resources-function.html#sam-specification-generated-resources-function-autopublishalias.

Just add AutoPublishAlias to AWS::Serverless::Function and SAM will create hash-based versions automatically than update CloudFront bindings.

Just rebuild lambda and run sam deploy:

Has @haydenk points out, just adding a new AWS::Lambda::Version works, and it's actually practical because you can remove the previous AWS::Lambda::Version in the same update, making it compatible with continuous deployment. Also the AutoPublishAlias is only available for SAM not CloudFormation.