(aws_s3_assets): unable to define bundling with local (python)

link to reference doc page

https://docs.aws.amazon.com/cdk/api/v2/python/aws_cdk.aws_s3_assets/README.html#asset-bundling

Describe your issue?

The documentation has an example which is not syntactically correct for Python:

assets.Asset(self, "BundledAsset",
    path="/path/to/asset",
    bundling={
        "local": {
            def try_bundle(self, output_dir, options):
                if can_run_locally:
                    # perform local bundling here
                    return True
                return False
        },
        # Docker bundling fallback
        "image": DockerImage.from_registry("alpine"),
        "entrypoint": ["/bin/sh", "-c"],
        "command": ["bundle"]
    }
)

The value for ‘bundling’ isn’t correct Python code. You can’t define a function in the middle of a dictionary.

I’ve attempted to determine how to correctly define this value, but haven’t been able to come up with the correct syntax. Based on the documentation, specific types are expected, so I tried constructing those types ahead of time:

class JinjaLocalBundling(ILocalBundling):
    def try_bundle(self, output_dir, options, *args, **kwargs) -> bool:
        print("Local Jinja2 Render:", self, output_dir, options, args, kwargs)
        return False

JinjaBundling = BundlingOptions(
    local=JinjaLocalBundling,
    image=DockerImage.from_registry("python3"),
    command=["python3 -m pip install jinja2"]
)

Then, including it in the Asset creation:

Asset(self, "BundleTest", path=os.path.join(dirname, "configure.jinja"),
      bundling=JinjaBundling)

This results in an error:

TypeError: Don't know how to convert object to JSON: <class 'test_app.test_stack.JinjaLocalBundling'>

There is very little documentation on how to do this correctly. Can someone demonstrate the correct way to use the bundling option for Asset definitions?

Overall Goal: I want to render a script to be executed as part of the EC2 User Data by replacing variables in the script with values from the stack. For example, I have a script which syncs data from an S3 bucket, but the S3 bucket name needs to be injected into the script. Something like this to replace {{ bucketname }} with the bucket defined by the CDK app:

aws s3 sync s3://{{ bucketname }}/path/ /tmp/path/

If there is an easier way to do this, please let me know. (but also fix the doc since it really doesn’t work)

Thanks!!

[alexpulver]

@rix0rrr the aws_s3_assets package overview documentation for Python generates the following signature for try_bundle method:

def try_bundle(self, output_dir, *, image, entrypoint=None, command=None, volumes=None, environment=None, workingDirectory=None, user=None, local=None, outputType=None, securityOpt=None, network=None):

Per my test and TypeScript documentation, it should be:

def try_bundle(self, output_dir, options):

Should I open a separate issue, or would you like to reopen this one?

Full working example:

import aws_cdk.aws_s3_assets as assets
import jsii
from aws_cdk import BundlingOptions, DockerImage, ILocalBundling

@jsii.implements(ILocalBundling)
class MyBundle:
    def try_bundle(self, output_dir, options):
        can_run_locally = True  # replace with actual logic
        if can_run_locally:
            # perform local bundling here
            return True
        return False

assets.Asset(
    self, "BundledAsset",
    path=str(pathlib.Path(__file__).parent.parent.joinpath("docs").resolve()),
    bundling=BundlingOptions(
        local=MyBundle(),
        # Docker bundling fallback
        image=DockerImage.from_registry("alpine"),
        entrypoint=["/bin/sh", "-c"],
        command=["bundle"]
    )
)

cc: @heitorlessa

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