Cancelling bundling of Lambda function causes next deployment to fail

[rtpascual]

Describe the bug

Cancelling cdk synth when a Lambda function is bundling can cause an empty bundling-temp-<hash> folder in cdk.out. This results in the next deployment of the Lambda to fail with InvalidParameterValueException: Uploaded file must be a non-empty zip.

Regression Issue

• Select this option if this issue appears to be a regression.

Last Known Working CDK Version

No response

Expected Behavior

CDK does not use existing bundling-temp folder if it is empty.

Current Behavior

CDK uses existing empty bundling-temp folder for deployment.

Reproduction Steps

1. Setup Amplify (Gen 2) https://docs.amplify.aws/react/start/manual-installation/
2. Setup a function https://docs.amplify.aws/react/build-a-backend/functions/set-up-function/
3. Run npx ampx sandbox --debug
4. Ctrl+C right when Bundling asset <Lambda>/Code/Stage... appears
5. Notice empty bundling-temp folder in cdk.out
6. Run npx ampx sandbox again

Possible Solution

No response

Additional Information/Context

We are seeing this for Amplify customers but I believe this can happen using only CDK for example in #18459 (comment).

CDK CLI Version

2.176.0

Framework Version

No response

Node.js Version

22.13.1

OS

Linux/Mac/Windows (More frequently on Windows from what we've seen)

Language

TypeScript

Language Version

No response

Other information

No response

[pahud]

Hi

I was not able to create the bundling-tmp folder in amplify but I get your point here.

Also, #18459 (comment) is still relevant in this case.
I'll bring it up to the team and request their input here.

[rix0rrr]

This is done to avoid duplicate work, but apparently we can't distinguish between unfinished and finished previous work.

The directory was probably called *-tmp-* to signal that it was unfinished, and it should have been rename()d to something not containing that string, and only the existence of the non-tmp directory should count as "work already done previously".

Should be a matter of unconditionally deleting the temp folder before starting bundling.

[samson-keung]

Some findings:

The following code creates the asset folders (e.g. cdk.out/asset.xxxxx:

aws-cdk/packages/aws-cdk-lib/core/lib/asset-staging.ts

Lines 418 to 426 in a486bbc

	private determineBundleDir(outdir: string, sourceHash?: string) {
	if (sourceHash) {
	return path.resolve(outdir, renderAssetFilename(sourceHash));
	}
	// When the asset hash isn't known in advance, bundler outputs to an
	// intermediate directory named after the asset's cache key
	return path.resolve(outdir, `bundling-temp-${this.cacheKey}`);
	}

and:

aws-cdk/packages/aws-cdk-lib/core/lib/asset-staging.ts

Lines 332 to 333 in a486bbc

	const bundleDir = this.determineBundleDir(this.assetOutdir, assetHash);
	this.bundle(bundling, bundleDir);

If the bundling is abruptly terminated (i.e. with Ctrl+C, the folder will not be populated with actual bundling output.

Then on the next bundling run, if the CDK bundling code sees the asset folder exists, it will skip re-bundling:

aws-cdk/packages/aws-cdk-lib/core/lib/asset-staging.ts

Lines 438 to 439 in a486bbc

	private bundle(options: BundlingOptions, bundleDir: string) {
	if (fs.existsSync(bundleDir)) { return; }

---

What I did to reproduce the issue:

1. I created a stack with a single resource:

new lambda.Function(this, 'LambdaFunction', {
      runtime: lambda.Runtime.NODEJS_LATEST,
      handler: 'index.handler',
      code: lambda.Code.fromAsset('src'), // put some random lambda code into `src/index.js`
    });

2. run cdk synth
3. delete the index.js in cdk.out/asset.xxxxxx to mimic the bundling logic being terminated and no bundled output got stored in the folder.
4. Run cdk synth again and observe that the cdk.out/asset.xxxxxx folder is still empty.

---

A workaround for now would be to remove the empty asset folder and re-ran cdk synth so the bundling logic can be executed again and fully completes.