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Cloud Development Kit

  • Define your cloud infrastructure using a familiar language:
    • JavaScript/TypeScript, Python, Java, and .NET
  • Contains high level components called constructs
  • The code is “compiled” into a CloudFormation template (JSON/YAML)
  • You can therefore deploy infrastructure and application runtime code together
    • Great for Lambda functions
    • Great for Docker containers in ECS / EKS

aws-cdk-ex

CDK in a diagram​

cdk-overview

CDK vs SAM​

  • SAM:
    • Serverless focused
    • Write your template declaratively in JSON or YAML
    • Great for quickly getting started with Lambda
    • Leverages CloudFormation
  • CDK:
    • All AWS services
    • Write infra in a programming language JavaScript/TypeScript, Python, Java, and .NET
    • Leverages CloudFormation

CDK + SAM​

  • You can use SAM CLI to locally test your CDK apps
  • You must first run cdk synth

cdk-and-sam

CDK Constructs​

  • CDK Construct is a component that encapsulates everything CDK needs to create the final CloudFormation stack
  • Can represent a single AWS resource (e.g., S3 bucket) or multiple related resources (e.g., worker queue with compute)
  • AWS Construct Library
    • A collection of Constructs included in AWS CDK which contains Constructs for every AWS resource
    • Contains 3 different levels of Constructs available (L1, L2, L3)
  • Construct Hub – contains additional Constructs from AWS, 3rd parties, and open-source CDK community

Layer 1 Constructs (L1)​

  • Can be called CFN Resources which represents all resources directly available in CloudFormation
  • Constructs are periodically generated from CloudFormation Resource Specification
  • Construct names start with Cfn (e.g., CfnBucket)
  • You must explicitly configure all resource proper ties
const bucket = new s3.CfnBucket(this, "MyBucket", { bucketName: "MyBucket" });

Layer 2 Constructs (L2)​

  • Represents AWS resources but with a higher level (intent-based API)
  • Similar functionality as L1 but with convenient defaults and boilerplate
    • You don’t need to know all the details about the resource proper ties
  • Provide methods that make it simpler to work with the resource (e.g., bucket.addLifeCycleRule())
const s3 = require("aws-cdk-lib/aws-s3");
const bucket = new s3.Bucket(this, "MyBucket", {
  versioned: true,
  encryption: s3.BucketEncryption.KMS,
});

// Returns the HTTPS URL of an S3 object
const objectUrl = bucket.urlForObject("MyBucket/MyObject");

Layer 3 Constructs (L3)​

  • Can be called Patterns, which represents multiple related resources
  • Helps you complete common tasks in AWS
  • Examples:
    • aws-apigateway.LambdaRestApi represents an API Gateway backed by a Lambda function
    • aws-ecs-patterns.ApplicationLoadBalancerFargateService which represents an architecture that includes a Fargate cluster with Application Load Balancer
const api = new apigateway.LambdaRestApi(this, "myapi", {
  handler: backend,
  proxy: false,
});

const items = api.root.addResource("items");
items.addMethod("GET"); // GET /items
items.addMethod("POST"); // POST /items

const item = items.addResource("{item}");
item.addMethod("GET"); // GET /items/{item}

item.addMethod("DELETE", new apigateway.HttpIntegration("http://amazon.com"));

Important Commands to know​

cdk-commands

Bootstrapping​

  • The process of provisioning resources for CDK before you can deploy CDK apps into an AWSenvironment
  • AWS Environment = account & region
  • CloudFormation Stack called CDKToolkit is created and contains:
    • S3 Bucket – to store files
    • IAM Roles – to grant permissions to perform deployments
  • You must run the following command for each new environment:
    • cdk bootstrap aws://<aws_account>/<aws_region>
  • Otherwise, you will get an error “Policy contains a statement with one or more invalid principal”

cdk-bootstrapping

Testing​

  • To test CDK apps, use CDK Assertions Module combined with popular test frameworks such as Jest (JavaScript) or Pytest (Python)
  • Verify we have specific resources, rules, conditions, parameters…
  • Two types of tests:
    • Fine-grained Assertions (common) – test specific aspects of the CloudFormation template (e.g., check if a resource has this property with this value)
    • Snapshot Tests – test the synthesized CloudFormation template against a previously stored baseline template
  • To import a template
    • Template.fromStack(MyStack) : stack built in CDK
    • Template.fromString(mystring) : stack build outside CDK

cdk-testing