Lacking examples of managing/deploying Python dependencies

❓ Guidance Question

The Question

As mentioned in aws/aws-cdk#3660, we are lacking a good example of a more realistic Lambda which includes dependencies. How should a developer ensure that handlers are packaged with their required dependencies? The current examples/boilerplate code only seems to demonstrate managing deployment code (i.e. cdk dependencies) but does not demonstrate best-practice for handling runtime dependencies.

Perhaps the correct solution is to utilize Lambda Layers to package dependencies? If so, it would be helpful to have that demonstrated in an example project.

Whatever the solution, it should demonstrate:

• separating runtime dependencies from build-time dependencies

Additionally, it would be nice if we could demonstrate:

• supporting the concept of packaging different handlers with only the dependencies that they need

[alukach]

@JamieMcKernanKaizen I ended up doing something like the following:

import os
import subprocess
from typing import List

from aws_cdk import (
    core,
    aws_lambda,
)

class MyStack(core.Stack):
    def __init__(
        self,
        scope: core.Construct,
        id: str,
        requirements_path: str = "./requirements.txt",
        layer_dir: str = "./.layer",
        **kwargs,
    ) -> None:
        super().__init__(scope, id, **kwargs)

        dependenciesLayer = self.create_dependencies_layer(
            requirements_path=requirements_path, output_dir=layer_dir
        )
        self.create_handler(
            layers=[dependenciesLayer],
        )

    def create_dependencies_layer(
        self, requirements_path: str, output_dir: str
    ) -> aws_lambda.LayerVersion:
        # Install requirements for layer
        if not os.environ.get("SKIP_PIP"):
            subprocess.check_call( 
                # Note: Pip will create the output dir if it does not exist
                f"pip install -r {requirements_path} -t {output_dir}/python".split()
            )
        return aws_lambda.LayerVersion(
            self, "HandlerDependencies", code=aws_lambda.Code.from_asset(output_dir)
        )
    
    def create_handler(
        self,
        layers: List[aws_lambda.LayerVersion],
    ):
        return aws_lambda.Function(
            self,
            "Some Function",
            code=aws_lambda.Code.from_asset('path/to/code'),
            handler='handlers.my_handler',
            runtime=aws_lambda.Runtime.PYTHON_3_7,
            layers=layers,
        )

[gmiretti]

Making an aws-samples/aws-cdk-examples for python using bundling would be great.

Mainly because the example code in section “Bundling asset code” in CDK Python docs (v 1.47.1) doesn’t work without some tweaking ( as published in https://docs.aws.amazon.com/cdk/api/latest/python/aws_cdk.aws_lambda.README.html#id3 )