Debugging a CDK Python Project in Visual Studio Code

Debugging a CDK (Cloud Development Kit) Python project in Visual Studio Code is straightforward once the environment is set up correctly. With a few configuration tweaks, you can step through your infrastructure code just like any other Python application.

Setting Up Your Visual Studio Code Environment

1. Install Necessary Extensions:

• Python Extension: Official Microsoft Python extension.
• AWS Toolkit: Helpful for interacting with AWS resources directly within the editor.

2. Create a Virtual Environment:

• Open the terminal.
• Run python -m venv .venv.
• Activate the environment:
  • Windows: .venv\Scripts\activate
  • macOS/Linux: source .venv/bin/activate
• Install project dependencies using pip install -r requirements.txt.

3. Verify CDK Installation: Ensure the AWS CDK CLI is installed globally:

npm install -g aws-cdk

Check the version with:

cdk --version

Configuring Launch.json for Debugging

To debug properly, Visual Studio Code needs a launch.json file:

Steps to Create launch.json:

• Open the Command Palette (Ctrl+Shift+P).
• Select Debug: Open launch.json.
• Choose Python environment.
• Modify the generated file to target the CDK app script.

Example launch.json setup:

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Python: CDK Debug",
      "type": "python",
      "request": "launch",
      "program": "${workspaceFolder}/app.py",
      "args": ["synth"],
      "console": "integratedTerminal",
      "justMyCode": false
    }
  ]
}

This configuration will run your app.py file with the argument synth, mimicking the CDK CLI behavior.

Best Practices for Effective Debugging

Breakpoints Placement:

• Set breakpoints inside your Stack classes.
• Focus on constructs like Bucket, Function, and custom resources.

Logging Infrastructure Values:

• Add print() statements to verify resource properties.
• Use Python’s built-in logging module for structured logs.

Environment Variables Handling:

• If your stack depends on environment variables, define them inside your launch configuration under env. Example:

"env": {
  "AWS_REGION": "us-east-1"
}

Common Issues and Solutions

Problem: Breakpoints Not Hit

• Confirm you are launching through Visual Studio Code’s debugger, not via terminal.
• Set "justMyCode": false to ensure the debugger does not skip over CDK internals.

Problem: CDK Context Missing

• Context passed during cdk synth isn’t always available when debugging.
• Manually create a cdk.json file in the root with necessary context values.

Problem: Dependency Import Errors

• Make sure the virtual environment is activated.
• Double-check settings.json to verify the correct Python interpreter is selected.

Workflow Tips

• Use Run and Debug view instead of starting CDK via terminal.
• Keep AWS credentials configured via environment variables or named profiles.
• Regularly clean synthesized outputs with cdk synth --quiet to reduce noise during debugging.

Final Thoughts

Visual Studio Code, combined with thoughtful configuration, makes debugging a CDK Python project highly efficient. By setting up the right tools, carefully placing breakpoints, and managing environment settings, you can troubleshoot infrastructure code confidently and efficiently without needing to shift contexts or guess about what happens during a deployment.