Welcome to your CDK Python project!

The cdk.json file tells the CDK Toolkit how to execute your app.

This project is set up like a standard Python project. The initialization process also creates a virtualenv within this project, stored under the .venv directory. To create the virtualenv it assumes that there is a python3 (or python for Windows) executable in your path with access to the venv package. If for any reason the automatic creation of the virtualenv fails, you can create the virtualenv manually.

To manually create a virtualenv on MacOS and Linux:

$ python3 -m venv .venv

After the init process completes and the virtualenv is created, you can use the following step to activate your virtualenv.

$ source .venv/bin/activate

If you are a Windows platform, you would activate the virtualenv like this:

% .venv\Scripts\activate.bat

Once the virtualenv is activated, you can install the required dependencies.

$ pip install -r requirements.txt

If we need a local PostgreSQL database, then use the below command to start PostgreSQL locally.

docker compose up -d

Some Python modules cannot be located by the lambda function. We need to create a zip of those modules and use them as a layer.

For that use below Docker command that is used to install Python dependencies in a way that is compatible with AWS Lambda.

• docker run -v "$PWD":/var/task "amazon/aws-sam-cli-build-image-python3.9" /bin/sh -c "pip install -r lambda/requirements.txt -t python/lib/python3.9/site-packages/; exit"

Then we need to create zip

• zip -r layers/pythonlib_layer.zip python

At this point you can now synthesize the CloudFormation template for this code.

$ cdk synth

To add additional dependencies, for example other CDK libraries, just add them to your setup.py file and rerun the pip install -r requirements.txt command.

Testing

• cdk synth > template.yaml
• sam build
• sam local invoke MyLambdaFunction --no-event -t ./cdk.out/AwsCdkPythonPsycopg2Stack.template.json
• Read : sam local invoke MyLambdaFunction --event events/read.json -t ./cdk.out/AwsCdkPythonPsycopg2Stack.template.json
• Write : sam local invoke MyLambdaFunction --event events/write.json -t ./cdk.out/AwsCdkPythonPsycopg2Stack.template.json

Payload

• Write

  {
      "action": "write",
      "data": {
          "name": "Sample Record",
          "description": "This is a test description."
      }
  }
  

• Read

  {
      "action": "read"
  }
  

Result

• Write

  (base) ➜  cdk-sam-demo git:(main) ✗ sam local invoke MyLambdaFunction --event events/write.json -t ./cdk.out/CdkSamDemoStack.template.json
  Invoking app.lambda_handler (python3.9)
  Decompressing
  /Users/santosh/Documents/workspace/aws/cdk-sam-demo/cdk.out/asset.b9e5b43dd3a267
  962ccec789725e1117a07177602f17375f57b5d4d009e20ff8.zip
  PyhonLibLayer9012B95C is a local Layer in the template
  Local image is up-to-date
  Building image.....................
  Using local image: samcli/lambda-python:3.9-x86_64-df98eaa0c4be380691b9d0fb2.
  
  Mounting
  /Users/santosh/Documents/workspace/aws/cdk-sam-demo/cdk.out/asset.5154647dfbc9e4
  d979237033784da0522eab6dd6532eef010dd6829545c8cb85 as /var/task:ro,delegated,
  inside runtime container
  START RequestId: 73cfbe98-e830-44f0-b72e-efb08227af7d Version: $LATEST
  END RequestId: e45b19ca-7ae7-4239-876f-22484bb3062c
  REPORT RequestId: e45b19ca-7ae7-4239-876f-22484bb3062c	Init Duration: 0.46 ms	Duration: 1501.97 ms	Billed Duration: 1502 ms	Memory Size: 256 MB	Max Memory Used: 256 MB
  {"statusCode": 200, "body": "{\"message\": \"Record created\", \"record_id\": 1}"}
  

• Read

  (base) ➜  cdk-sam-demo git:(main) ✗ sam local invoke MyLambdaFunction --event events/read.json -t ./cdk.out/CdkSamDemoStack.template.json
  Invoking app.lambda_handler (python3.9)
  Decompressing
  /Users/santosh/Documents/workspace/aws/cdk-sam-demo/cdk.out/asset.b9e5b43dd3a267
  962ccec789725e1117a07177602f17375f57b5d4d009e20ff8.zip
  PyhonLibLayer9012B95C is a local Layer in the template
  Local image is up-to-date
  Building image.....................
  Using local image: samcli/lambda-python:3.9-x86_64-df98eaa0c4be380691b9d0fb2.
  
  Mounting
  /Users/santosh/Documents/workspace/aws/cdk-sam-demo/cdk.out/asset.5154647dfbc9e4
  d979237033784da0522eab6dd6532eef010dd6829545c8cb85 as /var/task:ro,delegated,
  inside runtime container
  START RequestId: 7584b657-d6ea-4720-a0ca-5b659efe58a1 Version: $LATEST
  END RequestId: 307c58ab-fade-40ab-b28a-085fe2f6ad2c
  REPORT RequestId: 307c58ab-fade-40ab-b28a-085fe2f6ad2c	Init Duration: 0.47 ms	Duration: 1200.22 ms	Billed Duration: 1201 ms	Memory Size: 256 MB	Max Memory Used: 256 MB
  {"statusCode": 200, "body": "{\"records\": [{\"id\": 1, \"name\": \"Test Record\", \"description\": \"This is a test description.\"}]}"}
  

Useful commands

• cdk ls list all stacks in the app
• cdk synth emits the synthesized CloudFormation template
• cdk deploy deploy this stack to your default AWS account/region
• cdk diff compare deployed stack with current state
• cdk docs open CDK documentation

Enjoy!