Custom asset bundling for lambda using docker results in output code that is owned by root

[imtiazmangerah]

The custom asset bundling feature released in v1.45 -(#7898) results in output from the docker image that is owned by root (or the user that executes the commands in the docker container in general).

This is unexpected, and could be a problem if a user does not have root access on the machine to clean up the cdk.out folder.

Reproduction Steps

bundling_options = core.BundlingOptions(image=aws_lambda.Runtime.PYTHON_3_7.bundling_docker_image,
                                        command=[
                                            'bash', '-c',
                                            'pip install -r requirements.txt -t /asset-output && rsync -r . /asset-output',
                                        ])
source_code = aws_lambda.Code.from_asset('src/test', bundling=bundling_options)


handler = aws_lambda.Function(self, f"{self.id}-TestBundling",
                              function_name=f"{self.id}-TestBundling",
                              handler=f'handlers.test',
                              runtime=aws_lambda.Runtime.PYTHON_3_7,
                              code=source_code)

Error Log

executing ls -la in the output folder yeilds the following as an example

-rw-r--r--  1 root   root     573 Jun 11 06:03 handlers.py

Environment

• CLI Version :1.45.0 (build 0cfab15)
• Framework Version:1.45.0
• Node.js Version:v12.0.0
• **OS :Debian 10.4
• Language (Version):Python 3.7.6

Other

As per discussion on #7898, passing -u $UID:$UID as part of dockerArgs in packages/@aws-cdk/core/lib/bundling.ts might be the solution.

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This is 🐛 Bug Report