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What is this repo?

This repo is the code base used for the talk 'Live Coding Cloud Apps with CDK (infrastructure as code)'.

Following this README.md will guide you to create your first cloud application using AWS CDK. CDK is a development framework that will help you to write infrastructure as code using your favorite language (Typescript, Python, Javascript, Java, C# and others), for more information about CDK take a look at this.

The result of this live coding session can be find at the '/cloud-app-cdk/' directory. This is not production ready code and probably not the best styled code but it works when it comes to understand how to develop with CDK.

Thanks

It is inspired by cdkworkshop.com, @darkosubotica talks, cdkday.com, awsome-cdk repository and cdk.dev. I would like to thank all of them which provided a lot of resources that allowed me to learn the basis about CDK and bring it to my collegues.

Let's get started!

This document is intended to guide you in the process of building your first cloud application with CDK using Python so it is divided in a few sections where you will do something neecessary for the next section, this is better do not try to hurry up and avoid a section since you could regret it in the following ones.

Note: it is important to know that you need a AWS account with environment variables set with AWS credentials. Check it out awsume.

Install CDK toolkit

MacOS

Pre-requisites: brew

~ $ brew install node
~ $ npm i -g aws-cdk
~ $ cdk --version

Linux (Ubuntu 18.04 and 16.04)

~ $ sudo apt install nodejs
~ $ npm install -g aws-cdk
~ $ cdk --version

Init app && prepare virtualenv

Tipically CDK applications are developed in a local directory:

~ $ mkdir cloud-app-cdk
~ $ cd cloud-app-cdk

CDK toolkit helps you to initialize the app directory creating code base for you where you can start coding immediately.

~/cloud-app-cdk $ cdk init --language python
..
.
Executing Creating virtualenv...

As you probably observed CDK toolkit created a virtualenv for you so let's activate it. It is something you should do everytime you develop you application.

~/cloud-app-cdk $ source .venv/bin/activate

Before starting the actual CDK workflow it is necessary to install some core modules:

(.venv) ~/cloud-app-cdk $ pip install -r requirements.txt

CDK app structure

Well, first of all let's check what the CDK toolkit created for you.

README.md
app.py                                <--- CDK toolkit entry point
cdk.json                              <--- CDK toolkit configuration stuff
cloud_app_cdk/                        <--- cloud application code
requirements.txt
setup.py
source.bat

Your application's stack will be created in a very special file called 'cloud_app_cdk/cloud_app_cdk_stack.py'. More complex applications could be composed by more than one stack but in this case just one stack is needed.

Bootstraping your AWS account

CDK toolkit needs some AWS resources that will be used to deploy your application.

(.venv) ~/cloud-app-cdk $ cdk bootstrap

This will create a new AWS CloudFormation stack in your AWS account. It is only necessary to be run one time. Mainly this is a bucket to store artifacts.

Let's deploy something

At this point you will learn how to deploy something into your AWS account, let's start with a lambda function that will be useful in further phases.

AWS Lambda construct library

In order to be able to do it you need to install the Python module that will make the AWS Lambda construct library available which will allow you to use the AWS Lambda constructs in your CDK code.

(.venv) ~/cloud-app-cdk $ pip install aws-cdk.aws-lambda

Lambda code needs to be located in the CDK application root directory as follow:

(.venv) ~/cloud-app-cdk $ mkdir lambda

Hello World lambda

Code

Edit the following file where the lambda's code will be written:

(.venv) ~/cloud-app-cdk $ vim lambda/hello.py
import json

def handler(event, context):
    print('request: {}'.format(json.dumps(event)))
    return {
        'statusCode': 200,
        'headers': {
            'Content-Type': 'text/plain'
        },
        'body': 'Hello, CDK! You have hit {}\n'.format(event['path'])
    }

AWS resource

Now you are ready to create a new resource using the AWS Lambda construct library. Just edit the 'cloud_app_cdk/cloud_app_cdk_stack.py' file.

Import the AWS Lambda python module:

from aws_cdk import aws_lambda as _lambda

Create a new AWS Lambda resource like this:

class CloudAppCdkStack(core.Stack):

    def __init__(self, scope: core.Construct, id: str, **kwargs) -> None:
        super().__init__(scope, id, **kwargs)

        # Hello lambda
        hello_lambda = _lambda.Function(
            self, 'HelloHandler',
            runtime=_lambda.Runtime.PYTHON_3_8,
            code=_lambda.Code.asset('lambda'),
            handler='hello.handler',
            timeout=core.Duration.seconds(30)
        )

Deploy

Now it's time to deploy your CDK application for the first time.

(.venv) ~/cloud-app-cdk $ cdk deploy

You can check you AWS account at CloudFormation service and you will notice a new CloudFormation stack is created.

API Gateway

A typical resource necessary in cloud application is an API, this resource usually requires a lot of lines of code when you are coding AWS CloudFormation, however let's see how it looks in CDK.

Install API Gateway construct library

Again, you need to install the python package that contains the AWS APIGateway construct library. It is always you need to do when using a construct library.

(.venv) ~/cloud-app-cdk $ pip install aws-cdk.aws-apigateway

Add API Gateway resource

from aws_cdk import aws_apigateway as apigw
..
..
        # Hello lambda resource
        ..
        ..

        # API Gateway
        cloud_app_apigw = apigw.LambdaRestApi(
            self, 'Endpoint',
            handler=hello_lambda,
        )

Diff

Before trying to deploy again the changes let's see what is different between the local cdk application and the one deployed.

(.venv) ~/cloud-app-cdk $ cdk diff

Deploy

It looks good and obviously new resources are going to be deployed as shown in the 'cdk diff' before.

(.venv) ~/cloud-app-cdk $ cdk deploy cloud-app-cdk

New API gateway resources As you see it will add twelve new resources.

Test

Outputs:
cloud-app-cdk.Endpoint8024A810 = https://jmedoa58w2.execute-api.eu-west-1.amazonaws.com/pro

(.venv) ~/cloud-app-cdk $ curl https://jmedoa58w2.execute-api.eu-west-1.amazonaws.com/prod/
Hello, CDK! You have hit /

DynamoDB & Writing lambda & API Gateway Integration

(.venv) ~/cloud-app-cdk $ pip install aws-cdk.aws-dynamodb
from aws_cdk import aws_dynamodb as dynamodb
..
..
        # Dynamodb
        table = dynamodb.Table(
            self,
            'messages',
            partition_key=dynamodb.Attribute(
                name='author',
                type=dynamodb.AttributeType.STRING
            ),
            table_name='messages'
        )
..
..
        # Message lambda
        message_lambda = _lambda.Function(
            self, 'MessageHandler',
            runtime=_lambda.Runtime.PYTHON_3_8,
            code=_lambda.Code.asset('lambda'),
            handler='message.handler',
            timeout=core.Duration.seconds(30)
        )
        cloud_app_apigw_integration = apigw.LambdaIntegration(message_lambda)
        api_message = cloud_app_apigw.root.add_resource("message")
        api_message.add_method("POST", cloud_app_apigw_integration)

Message lambda code (message.py):

import os
import json
import boto3

def handler(event, context):
    table = os.environ.get('table')
    dynamodb = boto3.client('dynamodb')

    item = {
            "author":{'S':event["queryStringParameters"]["author"]},
            "message":{'S':event["queryStringParameters"]["message"]}
            }

    
    response = dynamodb.put_item(TableName=table,
            Item=item
            )

    message = 'Status of the write to DynamoDB {}!'.format(response)  
    return {
        "statusCode": 200,
        "body": json.dumps(message)
    }

Environmnet variables:

        # Message lambda
        message_lambda = _lambda.Function(
            self, 'MessageHandler',
            runtime=_lambda.Runtime.PYTHON_3_8,
            code=_lambda.Code.asset('lambda'),
            handler='message.handler',
            timeout=core.Duration.seconds(30),
            environment={'table': 'messages'}   <----------
        )

Reading lambda

        # Read lambda
        read_lambda = _lambda.Function(
            self, 'ReadHandler',
            runtime=_lambda.Runtime.PYTHON_3_8,
            code=_lambda.Code.asset('lambda'),
            handler='read.handler',
            timeout=core.Duration.seconds(30),
            environment={'table': 'messages'}
        )

        cloud_app_apigw_integration = apigw.LambdaIntegration(read_lambda)
        api_message = cloud_app_apigw.root.add_resource("read")
        api_message.add_method("GET", cloud_app_apigw_integration)

CFN Resources

        # L1 resources to add 'description'
        cfn_read_lambda = read_lambda.node.default_child
        cfn_read_lambda.description = "Messages reading lambda"

Read lambda code (read.py):

import os
import json
import boto3

def handler(event, context):
    table = os.environ.get('table')
    dynamodb = boto3.client('dynamodb')

    key = {
            "author":{'S':event["queryStringParameters"]["author"]}
            }

    response = dynamodb.get_item(TableName=table,
            Key=key
            )

    return {
        "statusCode": 200,
        "body": json.dumps(response["Item"])
    }

Permissions

        # Permissions
        table.grant_read_data(read_lambda)
        table.grant_write_data(message_lambda)

Last but not least deploy

(.venv) ~/cloud-app-cdk $ cdk deploy cloud-app-cdk

Test your app

Write a message (remember to use to correct endpoint):

(.venv) ~/cloud-app-cdk $ curl -X POST "https://ns1y3l5xji.execute-api.eu-west-1.amazonaws.com/prod/message?author=johndoe&message=helloworld"

Read a message

(.venv) ~/cloud-app-cdk $ curl -X GET "https://ns1y3l5xji.execute-api.eu-west-1.amazonaws.com/prod/read?author=johndoe"

Synth your first CDK application

~/cloud-app-cdk $ cdk synth

Clean your room

(.venv) ~/cloud-app-cdk $ cdk destroy
(.venv) ~/cloud-app-cdk $ deactivate
~/cloud-app-cdk $ cd ..
~/ $ rm -rf cloud-app-cdk