How to write CDK Outputs to a File

CDK Outputs - Introduction #

We often need to use outputs in our CDK stack and redirect the output to a file, so that we can then import some of the AWS resource identifiers in our frontend code (i.e. Api gateway URL, etc).

Writing CDK Outputs to a File #

In order to write CDK Outputs to a file we have to:

1. Use the CfnOutput construct to define the outputs
2. Use the --outputs-file flag when issuing the cdk deploy command to write the output values to a file

Here is a simple example of a CDK stack, that provisions an Output with the value of the region from the current CDK environment.

import * as cdk from '@aws-cdk/core';

export class CdkStarterStack extends cdk.Stack {
  constructor(scope: cdk.App, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    new cdk.CfnOutput(this, 'region', {value: cdk.Stack.of(this).region});
  }
}

Let's redirect the outputs from the stack to a file called cdk-outputs.json located in the root directory.

Run the cdk deploy command and specify the --outputs-file flag:

npx cdk deploy YOUR-STACK-NAME \
  --outputs-file ./cdk-outputs.json

After executing the deployment, the cdk-outputs.json file will be created in the root directory of your CDK App. The file's contents include your default aws region, i.e.:

{
  "cdk-stack": {
    "region": "us-east-1"
  }
}

The best way to keep our AWS resource identifiers in sync between the frontend and backend is to redirect our cdk outputs to a file, which can be directly imported and read from the frontend.

Further Reading #

• AWS CDK Tutorial for Beginners - Step-by-Step Guide
• How does AWS CDK work
• CDK Constructs - Complete Guide
• What is a Token in AWS CDK
• How to use Context in AWS CDK
• How to use Parameters in AWS CDK