(cloudfront): Function name is created non-deterministically

[laurelmay]

Describe the bug

Creating a CloudFront Function without specifying name can result in non-deterministic naming when the Node ID is relatively long. This results in unexpected function renames.

Expected Behavior

The method used to create a CloudFront Function name should be deterministic, predicable, and stable.

Current Behavior

The name of Functions is unstable, resulting in resource renames and snapshot failures.

Reproduction Steps

Run the following sample integration test several times. See that eventually it bounces between:

• AReallyLonIdIsAlsoPrettyLongIGuess25040025
• AReallyLoIdIsAlsoPrettyLongIGuess25040025
  for the name of the function.

import * as cdk from 'aws-cdk-lib';
import * as cloudfront from 'aws-cdk-lib/aws-cloudfront';
import * as integ from '@aws-cdk/integ-tests-alpha';

const app = new cdk.App();
const stack = new cdk.Stack(app, 'A-Really-Long-Stack-Name-Example');

const fn = new cloudfront.Function(stack, 'ExampleFunctionIdIsAlsoPrettyLongIGuess', {
  code: cloudfront.FunctionCode.fromInline('function handler(event) { return event.request }'),
});

new integ.IntegTest(app, 'FunctionNameLong', {
  testCases: [stack],
});

Possible Solution

aws-cdk/packages/aws-cdk-lib/aws-cloudfront/lib/function.ts

Lines 198 to 205 in 3656a4c

	private generateName(): string {
	const name = Stack.of(this).region + Names.uniqueId(this);
	if (name.length > 64) {
	return name.substring(0, 32) + name.substring(name.length - 32);
	}
	return name;
	}
	}

Should probably be reworked but that might result in yet again renaming functions. Names.uniqueResourceName should probably be used instead.

Additional Information/Context

This is also causing the failure on #28571

CDK CLI Version

2.118.0

Framework Version

2.118.0

Node.js Version

v20.2.0

OS

Linux

Language

TypeScript

Language Version

No response

Other information

No response

[pahud]

Yes I guess we should use Names.uniqueResourceName.

[laurelmay]

Actually making that change should be pretty trivial and non-disruptive; apparently function name resources require no interruption for updates. I'll work on the PR. https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-cloudfront-function.html#cfn-cloudfront-function-name

Edit: Just kidding... the CloudFormation docs are wrong. aws-cloudformation/cloudformation-coverage-roadmap#1893 has been opened to report the documentation issue.

[github-actions]

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