Your first AWS CDK app - AWS Cloud Development Kit (CDK) v1

This is the AWS CDK v1 Developer Guide. CDK v2 is now Generally Available. If you're using v2 (or just want to read about it), see the CDK v2 Developer Guide.

Your first AWS CDK app

You've read Getting started with the AWS CDK and set up your development environment for writing AWS CDK apps? Great! Now let's see how it feels to work with the AWS CDK by building the simplest possible AWS CDK app.

Note

The AWS CDK supports Go in a developer preview. This tutorial does not include instructions or code examples for Go.

In this tutorial, you'll learn about the structure of a AWS CDK project, how to use the AWS Construct Library to define AWS resources using code, and how to synthesize, diff, and deploy collections of resources using the AWS CDK Toolkit command-line tool.

The standard AWS CDK development workflow is similar to the workflow you're already familiar with as a developer, just with a few extra steps.

  1. Create the app from a template provided by the AWS CDK

  2. Add code to the app to create resources within stacks

  3. Build the app (optional; the AWS CDK Toolkit will do it for you if you forget)

  4. Synthesize one or more stacks in the app to create an AWS CloudFormation template

  5. Deploy one or more stacks to your AWS account

The build step catches syntax and type errors. The synthesis step catches logical errors in defining your AWS resources. The deployment may find permission issues. As always, you go back to the code, find the problem, fix it, then build, synthesize and deploy again.

Tip

Don't forget to keep your AWS CDK code under version control!

This tutorial walks you through creating and deploying a simple AWS CDK app, from initializing the project to deploying the resulting AWS CloudFormation template. The app contains one stack, which contains one resource: an Amazon S3 bucket.

We'll also show what happens when you make a change and re-deploy, and how to clean up when you're done.

Create the app

Each AWS CDK app should be in its own directory, with its own local module dependencies. Create a new directory for your app. Starting in your home directory, or another directory if you prefer, issue the following commands.

Important

Be sure to name your project directory hello-cdk, exactly as shown here. The AWS CDK project template uses the directory name to name things in the generated code, so if you use a different name, the code in this tutorial won't work.

mkdir hello-cdk cd hello-cdk

Now initialize the app using the cdk init command, specifying the desired template ("app") and programming language. That is:

TypeScript
cdk init app --language typescript
JavaScript
cdk init app --language javascript
Python
cdk init app --language python

After the app has been created, also enter the following two commands to activate the app's Python virtual environment and install the AWS CDK core dependencies.

source .venv/bin/activate python -m pip install -r requirements.txt
Java
cdk init app --language java

If you are using an IDE, you can now open or import the project. In Eclipse, for example, choose File > Import > Maven > Existing Maven Projects. Make sure that the project settings are set to use Java 8 (1.8).

C#
cdk init app --language csharp

If you are using Visual Studio, open the solution file in the src directory.

Tip

If you don't specify a template, the default is "app," which is the one we wanted anyway, so technically you can leave it out and save four keystrokes.

The cdk init command creates a number of files and folders inside the hello-cdk directory to help you organize the source code for your AWS CDK app. Take a moment to explore. The structure of a basic app is all there; you'll fill in the details in this tutorial.

If you have Git installed, each project you create using cdk init is also initialized as a Git repository. We'll ignore that for now, but it's there when you need it.

Build the app

In most programming environments, after making changes to your code, you'd build (compile) it. This isn't strictly necessary with the AWS CDK—the Toolkit does it for you so you can't forget. But you can still build manually whenever you want to catch syntax and type errors. For reference, here's how.

TypeScript
npm run build
JavaScript

No build step is necessary.

Python

No build step is necessary.

Java
mvn compile -q

Or press Control-B in Eclipse (other Java IDEs may vary)

C#
dotnet build src

Or press F6 in Visual Studio

Note

If your project was created with an older version of the AWS CDK Toolkit, it may not automatically build when you run it. If changes you make in your code fail to be reflected in the synthesized template, try a manual build. Make sure you are using the latest available version of the AWS CDK for this tutorial.

List the stacks in the app

Just to verify everything is working correctly, list the stacks in your app.

cdk ls

If you don't see HelloCdkStack, make sure you named your app's directory hello-cdk. If you didn't, go back to Create the app and try again.

Add an Amazon S3 bucket

At this point, your app doesn't do anything because the stack it contains doesn't define any resources. Let's add an Amazon S3 bucket.

Install the Amazon S3 package from the AWS Construct Library.

TypeScript
npm install @aws-cdk/aws-s3
JavaScript
npm install @aws-cdk/aws-s3
Python
pip install aws-cdk.aws-s3
Java

Add the following to the <dependencies> container of pom.xml.

<dependency> <groupId>software.amazon.awscdk</groupId> <artifactId>s3</artifactId> <version>${cdk.version}</version> </dependency>
Tip

If you are using a Java IDE, it probably has a simpler way to add this dependency to your project, such as a GUI for editing the POM. We recommend editing pom.xml by hand because of the use of the cdk.version variable, which helps keep the versions of installed modules consistent.

C#

Run the following command in the src/HelloCdk directory.

dotnet add package Amazon.CDK.AWS.S3

Or Tools > NuGet Package Manager > Manage NuGet Packages for Solution in Visual Studio, then locate and install the Amazon.CDK.AWS.S3 package

Next, define an Amazon S3 bucket in the stack using the Bucket construct.

TypeScript

In lib/hello-cdk-stack.ts:

import * as cdk from '@aws-cdk/core'; import * as s3 from '@aws-cdk/aws-s3'; export class HelloCdkStack extends cdk.Stack { constructor(scope: cdk.App, id: string, props?: cdk.StackProps) { super(scope, id, props); new s3.Bucket(this, 'MyFirstBucket', { versioned: true }); } }
JavaScript

In lib/hello-cdk-stack.js:

const cdk = require('@aws-cdk/core'); const s3 = require('@aws-cdk/aws-s3'); class HelloCdkStack extends cdk.Stack { constructor(scope, id, props) { super(scope, id, props); new s3.Bucket(this, 'MyFirstBucket', { versioned: true }); } } module.exports = { HelloCdkStack }
Python

Add the following import statement in hello_cdk/hello_cdk_stack.py in the hello_cdk directory below the existing imports.

from aws_cdk import aws_s3 as s3

Replace the comment with the following code.

bucket = s3.Bucket(self, "MyFirstBucket", versioned=True,)
Java

In src/main/java/com/myorg/HelloCdkStack.java:

package com.myorg; import software.amazon.awscdk.core.*; import software.amazon.awscdk.services.s3.Bucket; public class HelloCdkStack extends Stack { public HelloCdkStack(final Construct scope, final String id) { this(scope, id, null); } public HelloCdkStack(final Construct scope, final String id, final StackProps props) { super(scope, id, props); Bucket.Builder.create(this, "MyFirstBucket") .versioned(true).build(); } }
C#

In src/HelloCdk/HelloCdkStack.cs:

using Amazon.CDK; using Amazon.CDK.AWS.S3; namespace HelloCdk { public class HelloCdkStack : Stack { public HelloCdkStack(Construct scope, string id, IStackProps props=null) : base(scope, id, props) { new Bucket(this, "MyFirstBucket", new BucketProps { Versioned = true }); } } }

Bucket is the first construct we've seen, so let's take a closer look. Like all constructs, the Bucket class takes three parameters.

  • scope: Tells the bucket that the stack is its parent: it is defined within the scope of the stack. You can define constructs inside of constructs, creating a hierarchy (tree). Here, and in most cases, the scope is this (self in Python), meaning the construct that contains the bucket: the stack.

  • Id: The logical ID of the Bucket within your AWS CDK app. This (plus a hash based on the bucket's location within the stack) uniquely identifies the bucket across deployments so the AWS CDK can update it if you change how it's defined in your app. Here it is "MyFirstBucket." Buckets can also have a name, which is separate from this ID (it's the bucketName property).

  • props: A bundle of values that define properties of the bucket. Here we've defined only one property: versioned, which enables versioning for the files in the bucket.

All constructs take these same three arguments, so it's easy to stay oriented as you learn about new ones. And as you might expect, you can subclass any construct to extend it to suit your needs, or just to change its defaults.

Tip

If a construct's props are all optional, you can omit the props parameter entirely.

Props are represented differently in the languages supported by the AWS CDK.

  • In TypeScript and JavaScript, props is a single argument and you pass in an object containing the desired properties.

  • In Python, props are passed as keyword arguments.

  • In Java, a Builder is provided to pass the props. Two, actually; one for BucketProps, and a second for Bucket to let you build the construct and its props object in one step. This code uses the latter.

  • In C#, you instantiate a BucketProps object using an object initializer and pass it as the third parameter.

Synthesize an AWS CloudFormation template

Synthesize an AWS CloudFormation template for the app, as follows.

cdk synth

If your app contained more than one stack, you'd need to specify which stack(s) to synthesize. But since it only contains one, the CDK Toolkit knows you must mean that one.

Tip

If you received an error like --app is required..., it's probably because you are running the command from a subdirectory. Navigate to the main app directory and try again.

The cdk synth command executes your app, which causes the resources defined in it to be translated into an AWS CloudFormation template. The displayed output of cdk synth is a YAML-format template; the beginning of our app's output is shown below. The template is also saved in the cdk.out directory in JSON format.

Resources:
  MyFirstBucketB8884501:
    Type: AWS::S3::Bucket
    Properties:
      VersioningConfiguration:
        Status: Enabled
    UpdateReplacePolicy: Retain
    DeletionPolicy: Retain
    Metadata:...

Even if you aren't very familiar with AWS CloudFormation, you should be able to find the definition for the bucket and see how the versioned property was translated.

Note

Every generated template contains a AWS::CDK::Metadata resource by default. (We haven't shown it here.) The AWS CDK team uses this metadata to gain insight into how the AWS CDK is used, so we can continue to improve it. For details, including how to opt out of version reporting, see Version reporting.

The cdk synth generates a perfectly valid AWS CloudFormation template. You could take it and deploy it using the AWS CloudFormation console or another tool. But the AWS CDK Toolkit can also do that.

Deploying the stack

To deploy the stack using AWS CloudFormation, issue:

cdk deploy

As with cdk synth, you don't need to specify the name of the stack since there's only one in the app.

It is optional (though good practice) to synthesize before deploying. The AWS CDK synthesizes your stack before each deployment.

If your code has security implications, you'll see a summary of these and need to confirm them before deployment proceeds. This isn't the case in our stack.

cdk deploy displays progress information as your stack is deployed. When it's done, the command prompt reappears. You can go to the AWS CloudFormation console and see that it now lists HelloCdkStack. You'll also find MyFirstBucket in the Amazon S3 console.

You've deployed your first stack using the AWS CDK—congratulations! But that's not all there is to the AWS CDK.

Modifying the app

The AWS CDK can update your deployed resources after you modify your app. Let's change our bucket so it can be automatically deleted when we delete the stack, which involves changing its RemovalPolicy. Also, because AWS CloudFormation won't delete Amazon S3 buckets that contain any objects, we'll ask the AWS CDK to delete the objects from our bucket before destroying the bucket, via the autoDeleteObjects property.

TypeScript

Update lib/hello-cdk-stack.ts.

new s3.Bucket(this, 'MyFirstBucket', { versioned: true, removalPolicy: cdk.RemovalPolicy.DESTROY, autoDeleteObjects: true });
JavaScript

Update lib/hello-cdk-stack.js.

new s3.Bucket(this, 'MyFirstBucket', { versioned: true, removalPolicy: cdk.RemovalPolicy.DESTROY, autoDeleteObjects: true });
Python

Update hello_cdk/hello_cdk_stack.py.

bucket = s3.Bucket(self, "MyFirstBucket", versioned=True, removal_policy=core.RemovalPolicy.DESTROY, auto_delete_objects=True)
Java

Update src/main/java/com/myorg/HelloCdkStack.java, adding the new import and updating the bucket definition in the appropriate places.

import software.amazon.awscdk.core.RemovalPolicy;
Bucket.Builder.create(this, "MyFirstBucket") .versioned(true) .removalPolicy(RemovalPolicy.DESTROY) .autoDeleteObjects(true) .build();
C#

Update src/HelloCdk/HelloCdkStack.cs.

new Bucket(this, "MyFirstBucket", new BucketProps { Versioned = true, RemovalPolicy = RemovalPolicy.DESTROY, AutoDeleteObjects = true });

Here, we haven't written any code that, in itself, changes our Amazon S3 bucket. Instead, our code defines the desired state of the bucket. The AWS CDK synthesizes that state to a new AWS CloudFormation template and deploys a changeset that makes only the changes necessary to reach that state.

To see these changes, we'll use the cdk diff command .

cdk diff

The AWS CDK Toolkit queries your AWS account for the last-deployed AWS CloudFormation template for the HelloCdkStack and compares it with the template it just synthesized from your app. The output should look like the following.

Stack HelloCdkStack
IAM Statement Changes
┌───┬──────────────────────────────┬────────┬──────────────────────────────┬──────────────────────────────┬───────────┐
│   │ Resource                     │ Effect │ Action                       │ Principal                    │ Condition │
├───┼──────────────────────────────┼────────┼──────────────────────────────┼──────────────────────────────┼───────────┤
│ + │ ${Custom::S3AutoDeleteObject │ Allow  │ sts:AssumeRole               │ Service:lambda.amazonaws.com │           │
│   │ sCustomResourceProvider/Role │        │                              │                              │           │
│   │ .Arn}                        │        │                              │                              │           │
├───┼──────────────────────────────┼────────┼──────────────────────────────┼──────────────────────────────┼───────────┤
│ + │ ${MyFirstBucket.Arn}         │ Allow  │ s3:DeleteObject*             │ AWS:${Custom::S3AutoDeleteOb │           │
│   │ ${MyFirstBucket.Arn}/*       │        │ s3:GetBucket*                │ jectsCustomResourceProvider/ │           │
│   │                              │        │ s3:GetObject*                │ Role.Arn}                    │           │
│   │                              │        │ s3:List*                     │                              │           │
└───┴──────────────────────────────┴────────┴──────────────────────────────┴──────────────────────────────┴───────────┘
IAM Policy Changes
┌───┬────────────────────────────────────────────────────────┬────────────────────────────────────────────────────────┐
│   │ Resource                                               │ Managed Policy ARN                                     │
├───┼────────────────────────────────────────────────────────┼────────────────────────────────────────────────────────┤
│ + │ ${Custom::S3AutoDeleteObjectsCustomResourceProvider/Ro │ {"Fn::Sub":"arn:${AWS::Partition}:iam::aws:policy/serv │
│   │ le}                                                    │ ice-role/AWSLambdaBasicExecutionRole"}                 │
└───┴────────────────────────────────────────────────────────┴────────────────────────────────────────────────────────┘
(NOTE: There may be security-related changes not in this list. See https://github.com/aws/aws-cdk/issues/1299)

Parameters
[+] Parameter AssetParameters/4cd61014b71160e8c66fe167e43710d5ba068b80b134e9bd84508cf9238b2392/S3Bucket AssetParameters4cd61014b71160e8c66fe167e43710d5ba068b80b134e9bd84508cf9238b2392S3BucketBF7A7F3F: {"Type":"String","Description":"S3 bucket for asset \"4cd61014b71160e8c66fe167e43710d5ba068b80b134e9bd84508cf9238b2392\""}
[+] Parameter AssetParameters/4cd61014b71160e8c66fe167e43710d5ba068b80b134e9bd84508cf9238b2392/S3VersionKey AssetParameters4cd61014b71160e8c66fe167e43710d5ba068b80b134e9bd84508cf9238b2392S3VersionKeyFAF93626: {"Type":"String","Description":"S3 key for asset version \"4cd61014b71160e8c66fe167e43710d5ba068b80b134e9bd84508cf9238b2392\""}
[+] Parameter AssetParameters/4cd61014b71160e8c66fe167e43710d5ba068b80b134e9bd84508cf9238b2392/ArtifactHash AssetParameters4cd61014b71160e8c66fe167e43710d5ba068b80b134e9bd84508cf9238b2392ArtifactHashE56CD69A: {"Type":"String","Description":"Artifact hash for asset \"4cd61014b71160e8c66fe167e43710d5ba068b80b134e9bd84508cf9238b2392\""}

Resources
[+] AWS::S3::BucketPolicy MyFirstBucket/Policy MyFirstBucketPolicy3243DEFD
[+] Custom::S3AutoDeleteObjects MyFirstBucket/AutoDeleteObjectsCustomResource MyFirstBucketAutoDeleteObjectsCustomResourceC52FCF6E
[+] AWS::IAM::Role Custom::S3AutoDeleteObjectsCustomResourceProvider/Role CustomS3AutoDeleteObjectsCustomResourceProviderRole3B1BD092
[+] AWS::Lambda::Function Custom::S3AutoDeleteObjectsCustomResourceProvider/Handler CustomS3AutoDeleteObjectsCustomResourceProviderHandler9D90184F
[~] AWS::S3::Bucket MyFirstBucket MyFirstBucketB8884501
 ├─ [~] DeletionPolicy
 │   ├─ [-] Retain
 │   └─ [+] Delete
 └─ [~] UpdateReplacePolicy
     ├─ [-] Retain
     └─ [+] Delete

This diff has four sections.

  • IAM Statement Changes and IAM Policy Changes - These permission changes are there because we set the AutoDeleteObjects property on our Amazon S3 bucket. The auto-delete feature uses a custom resource to delete the objects in the bucket before the bucket itself is deleted. The IAM objects grant the custom resource's code access to the bucket.

  • Parameters - The AWS CDK uses these entries to locate the Lambda function asset for the custom resource.

  • Resources - The new and changed resources in this stack. We can see the aforementioned IAM objects, the custom resource ,and its associated Lambda function being added. We can also see that the bucket's DeletionPolicy and UpdateReplacePolicy attributes are being updated. These allow the bucket to be deleted along with the stack, and to be replaced with a new one.

You may be curious about why we specified RemovalPolicy in our AWS CDK app but got a DeletionPolicy property in the resulting AWS CloudFormation template. The AWS CDK uses a different name for the property because the AWS CDK default is to retain the bucket when the stack is deleted, while AWS CloudFormation's default is to delete it. See Removal policies for further details.

It's informative to compare the output of cdk synth here with the previous output and see the many additional lines of AWS CloudFormation template that the AWS CDK generated for us based on these relatively small changes.

Important

Since the autoDeleteObjects property is implemented using a AWS CloudFormation custom resource, which is implemented using an AWS Lambda function, our stack contains an asset. This fact requires that our AWS account and region be bootstrapped so that there's an Amazon S3 bucket to hold the asset during deployment. If you haven't already bootstrapped, issue:

cdk bootstrap aws://ACCOUNT-NUMBER/REGION

Now let's deploy.

cdk deploy

The AWS CDK warns you about the security policy changes we've already seen in the diff. Enter y to approve the changes and deploy the updated stack. The CDK Toolkit updates the bucket configuration as you requested.

HelloCdkStack: deploying...
[0%] start: Publishing 4cd61014b71160e8c66fe167e43710d5ba068b80b134e9bd84508cf9238b2392:current
[100%] success: Published 4cd61014b71160e8c66fe167e43710d5ba068b80b134e9bd84508cf9238b2392:current
HelloCdkStack: creating CloudFormation changeset...
 0/5 | 4:32:31 PM | UPDATE_IN_PROGRESS   | AWS::CloudFormation::Stack  | HelloCdkStack User Initiated
 0/5 | 4:32:36 PM | CREATE_IN_PROGRESS   | AWS::IAM::Role              | Custom::S3AutoDeleteObjectsCustomResourceProvider/Role (CustomS3AutoDeleteObjectsCustomResourceProviderRole3B1BD092)
 1/5 | 4:32:36 PM | UPDATE_COMPLETE      | AWS::S3::Bucket             | MyFirstBucket (MyFirstBucketB8884501)
 1/5 | 4:32:36 PM | CREATE_IN_PROGRESS   | AWS::IAM::Role              | Custom::S3AutoDeleteObjectsCustomResourceProvider/Role (CustomS3AutoDeleteObjectsCustomResourceProviderRole3B1BD092) Resource creation Initiated
 3/5 | 4:32:54 PM | CREATE_COMPLETE      | AWS::IAM::Role              | Custom::S3AutoDeleteObjectsCustomResourceProvider/Role (CustomS3AutoDeleteObjectsCustomResourceProviderRole3B1BD092)
 3/5 | 4:32:56 PM | CREATE_IN_PROGRESS   | AWS::Lambda::Function       | Custom::S3AutoDeleteObjectsCustomResourceProvider/Handler (CustomS3AutoDeleteObjectsCustomResourceProviderHandler9D90184F)
 3/5 | 4:32:56 PM | CREATE_IN_PROGRESS   | AWS::S3::BucketPolicy       | MyFirstBucket/Policy (MyFirstBucketPolicy3243DEFD)
 3/5 | 4:32:56 PM | CREATE_IN_PROGRESS   | AWS::Lambda::Function       | Custom::S3AutoDeleteObjectsCustomResourceProvider/Handler (CustomS3AutoDeleteObjectsCustomResourceProviderHandler9D90184F) Resource creation Initiated
 3/5 | 4:32:57 PM | CREATE_COMPLETE      | AWS::Lambda::Function       | Custom::S3AutoDeleteObjectsCustomResourceProvider/Handler (CustomS3AutoDeleteObjectsCustomResourceProviderHandler9D90184F)
 3/5 | 4:32:57 PM | CREATE_IN_PROGRESS   | AWS::S3::BucketPolicy       | MyFirstBucket/Policy (MyFirstBucketPolicy3243DEFD) Resource creation Initiated
 4/5 | 4:32:57 PM | CREATE_COMPLETE      | AWS::S3::BucketPolicy       | MyFirstBucket/Policy (MyFirstBucketPolicy3243DEFD)
 4/5 | 4:32:59 PM | CREATE_IN_PROGRESS   | Custom::S3AutoDeleteObjects | MyFirstBucket/AutoDeleteObjectsCustomResource/Default (MyFirstBucketAutoDeleteObjectsCustomResourceC52FCF6E)
 5/5 | 4:33:06 PM | CREATE_IN_PROGRESS   | Custom::S3AutoDeleteObjects | MyFirstBucket/AutoDeleteObjectsCustomResource/Default (MyFirstBucketAutoDeleteObjectsCustomResourceC52FCF6E) Resource creation Initiated
 5/5 | 4:33:06 PM | CREATE_COMPLETE      | Custom::S3AutoDeleteObjects | MyFirstBucket/AutoDeleteObjectsCustomResource/Default (MyFirstBucketAutoDeleteObjectsCustomResourceC52FCF6E)
 5/5 | 4:33:08 PM | UPDATE_COMPLETE_CLEA | AWS::CloudFormation::Stack  | HelloCdkStack
 6/5 | 4:33:09 PM | UPDATE_COMPLETE      | AWS::CloudFormation::Stack  | HelloCdkStack

 ✅  HelloCdkStack

Stack ARN:
arn:aws:cloudformation:REGION:ACCOUNT:stack/HelloCdkStack/UNIQUE-ID

Destroying the app's resources

Now that you're done with the quick tour, destroy your app's resources to avoid incurring any costs from the bucket you created, as follows.

cdk destroy

Enter y to approve the changes and delete any stack resources.

Note

If we hadn't changed the bucket's RemovalPolicy, the stack deletion would complete successfully, but the bucket would become orphaned (no longer associated with the stack).

Next steps

Where do you go now that you've dipped your toes in the AWS CDK?

The AWS CDK is an open-source project. Want to contribute?