Deploy a CloudFormation stack containing an autopublished CloudFront function without updating the associated CloudFront distribution if the function is unchanged

Question

I am using AWS CloudFormation to deploy a stack containing a CloudFront distribution using a CloudFront function. The template contains the following entries:
```yaml
CloudFrontFunction:
  Type: "AWS::CloudFront::Function"
  Properties:
    Name: "my-function"
    AutoPublish: true
    FunctionConfig:
      Comment: "My function"
      Runtime: "cloudfront-js-1.0"
    FunctionCode: |
      function handler(event) { /* ommitted for brievity */ }
CloudFrontDistribution:
  Type: "AWS::CloudFront::Distribution"
  Properties:
    ...
    DefaultCacheBehavior:
      FunctionAssociations:
        - EventType: "viewer-request"
          FunctionARN:
            "Fn::GetAtt": "CloudFrontFunction.FunctionARN"
```
Each time I deploy the stack using this template, CloudFormation updates the CloudFront function even if the function has not changed (I suspect this is caused by AutoPublish: true, but I need this setting to be enabled).

This results in CloudFormation also updating the distribution, which takes several minutes, and often simply fails (my guess is that the CloudFront API is not very reliable during peak traffic hours), resulting in our CD pipeline also failing.

Is there a way to avoid this behavior (e.g. do not publish the function if it has not changed)? I might put the function in another template/stack and keep this stack outside of our CD pipeline, but it's tedious to have to handle the function updates manually.

Answer

```
  CloudFrontFunction:
    Type: "AWS::CloudFront::Function"
    Properties:
      Name: "my-function"
      AutoPublish: true
      FunctionConfig:
        Comment: "My function"
        Runtime: "cloudfront-js-1.0"
      FunctionCode: !Sub |
        function handler(event) {
            var request = event.request;

var response = "string"; // Create the response object here,
                                // using the request properties if needed.

return response;
        }
```
Hi there,

I understand that you suspect the AutoPublish: true[1] caused the CFN stack triggers the update on this resource every time a stack update operation triggered.

It is not the case and I confirmed with code snippet above, when there is no literal changes to the AWS::CloudFront::Function, it will not be updated. How a property is defined in a resource type has nothing to do with how CloudFormation judge if there are changes to make in next operation, unless you have addition Transform features integrated into the template. Based on your code snippet, looks like you are using inline code for the CF-Function, please scrutinize if there are changes made between two stack update operations.

To decide a resource in the stack requires update or not, CFN service simple performs "create changeset" mechanism before stack operation, only literal changes detected for a resource so it will be put in to the changeset-resources require update.

If no obvious changes you can observe, please consider:
1. Do you have Transform in the template
2. Does the inline code referring to a Parameter or other resources that require update each operation

If still struggle, please consider create a support ticket to AWS support for stack in-depth check.

References:
[1] https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-cloudfront-function.html#aws-resource-cloudfront-function-properties

Deploy a CloudFormation stack containing an autopublished CloudFront function without updating the associated CloudFront distribution if the function is unchanged

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