Project: CDK Init

Goal

Initialize a CDK Python project that will serve as the deployment foundation for the 10Q Inference module. By the end of this project you will have a working CDK app that synthesizes a valid CloudFormation template, even though it deploys no resources yet. The 10Q Inference project builds on top of this skeleton.

Contract

This project produces infrastructure code, not a Lambda function. There is no request/response contract here. The Lambda functions you deploy in later modules conform to the Lambda Contract — the CDK stack is the mechanism that deploys them.

The model your Lambda will invoke is defined in Models. You will reference that page when adding Bedrock permissions in the next module.

Required Reading

• Why CDK? — the preceding page in this module

• AWS CDK Getting Started (Python) — official install and bootstrapping guide

• AWS CDK API Reference — aws-cdk-lib — construct library documentation

Constraints

• Use Python 3.12 as both the CDK app language and the target Lambda runtime in later stacks.

• Install the CDK CLI globally via npm (npm install -g aws-cdk). Do not use a Python-packaged CDK CLI wrapper.

• Use CDK v2 (aws-cdk-lib). Do not use CDK v1 individual packages.

• The project must synthesize cleanly (cdk synth exits zero and produces a valid template) before you consider this project complete.

• Do not deploy to AWS yet. cdk synth and cdk diff are sufficient for this project. Deployment happens in the 10Q Inference module.

Acceptance Criteria

1. Running cdk init app --language python in a fresh directory produces a working project skeleton.

2. The project uses a Python 3.12 virtual environment with dependencies installed from requirements.txt.

3. cdk synth produces a CloudFormation template in cdk.out/ without errors.

4. The generated stack class is in a Python module under the project directory (not in app.py directly).

5. You can explain what each generated file does — app.py, the stack module, cdk.json, requirements.txt, and the tests/ directory.

Hints

Installing the CDK CLI

npm install -g aws-cdk
cdk --version

You need Node.js 18 or later. The CDK CLI is a Node package regardless of which language your CDK app uses.

Bootstrapping your AWS account

Before any CDK app can deploy (in later modules), the target account/region needs a one-time bootstrap:

cdk bootstrap aws://<ACCOUNT_ID>/<REGION>

This creates an S3 bucket and IAM roles that CDK uses for deployments. Run it once per account/region pair. You do not need to bootstrap for cdk synth — only for cdk deploy.

Initializing the project

mkdir cdk-10q-inference
cd cdk-10q-inference
cdk init app --language python

This generates:

File/Directory	Purpose
app.py	Entry point — instantiates the CDK app and your stack
cdk_10q_inference/	Python package containing your stack class
cdk_10q_inference/cdk_10q_inference_stack.py	The stack definition (where you add resources)
cdk.json	CDK configuration — tells the CLI how to run your app
requirements.txt	Python dependencies (aws-cdk-lib, constructs)
requirements-dev.txt	Dev dependencies (e.g., pytest)
tests/	Test directory with a placeholder unit test

Activating the virtual environment

After cdk init, activate the generated virtual environment and install dependencies:

python3.12 -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt

Use Python 3.12 explicitly. If your system default is a different version, specify the full path or use python3.12 directly.

Verifying the skeleton

cdk synth

This runs app.py, which instantiates your stack, and outputs the synthesized CloudFormation template to stdout. It also writes the full output to cdk.out/. If this exits zero, your project structure is correct.

Understanding app.py

The entry point is minimal — it creates a cdk.App, instantiates your stack class, and calls app.synth(). All resource definitions belong in the stack class, not in app.py.

The stack class

Open the generated stack file (e.g., cdk_10q_inference/cdk_10q_inference_stack.py). It subclasses Stack and currently has an empty __init__. In the next module you will add Lambda functions, S3 buckets, and IAM policies here.

What cdk.json controls

The app field in cdk.json tells the CDK CLI how to execute your app:

{
  "app": "python3 app.py"
}

If you renamed app.py or need to pass environment variables, this is where you configure it.

Next step

Once cdk synth succeeds with no errors, this project is complete. The 10Q Inference module picks up from this skeleton and adds the actual Lambda and supporting resources.

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Last verified: 2026-06