How to wait stack to complete before executing code in AWS CDK?

Question

I'm trying AWS CDK and got stuck when I tried to execute a code block that depends on the stack completion.

Here's my current code:

class Application extends cdk.Construct {
    constructor(scope: cdk.Construct, id: string) {
        super(scope, id);
        const webStack = new WebsiteStack(app, `website-stack-${id}`, { stage: id })
        const buildStack = new CodeBuildStack(app, `codebuild-stack-${id}`, { stage:id, bucket: webStack.websiteBucket, distribution: webStack.websiteDistribution });
        this.generateBuildParameter(id, webStack, buildStack)
    }

    generateBuildParameter(id: string, webStack: WebsiteStack, buildStack: CodeBuildStack) {
        const buildParam = {
            projectName: buildStack.buildProject.projectName,
            sourceVersion: id,
            environmentVariablesOverride: [
              { name: "STAGE", value: id, type: "PLAINTEXT" },
              { name: "WEBSITE_BUCKET", value: webStack.websiteBucket.bucketName, type: "PLAINTEXT" },
              { name: "CLOUDFRONT_DISTRIBUTION_ID", value: webStack.websiteDistribution.distributionId, "type": "PLAINTEXT" }
            ],
            buildspecOverride: "./buildspec.yml"
        }
        fse.outputJson(`./cdk.out/build-parameters/build-${id}.json`, buildParam, (err: Error) => {
            if (err) {
                throw err
            };
            console.log(`build parameter has been created in "../cdk.out/build-parameters/build-${id}.json"`);
        })
    }
}

I'm just trying to generate a json file that depends on the buildStack . However, it seems that it's not waiting for the stack to complete.

Here's my current output:

{
   "projectName":"${Token[TOKEN.41]}",
   "sourceVersion":"master",
   "environmentVariablesOverride":[{"name":"STAGE","value":"master","type":"PLAINTEXT"},{"name":"WEBSITE_BUCKET","value":"${Token[TOKEN.17]}","type":"PLAINTEXT"},{"name":"CLOUDFRONT_DISTRIBUTION_ID","value":"${Token[TOKEN.26]}","type":"PLAINTEXT"}],
   "buildspecOverride":"./buildspec.yml"
}

Does AWS CDK support Promise or some sort to wait the stack to be completed?

Answer 1

If you're trying to reference 'dynamic' things like the CloudFront distribution Id that will be generated, I would probably try to have 2 different stacks, and have one depend on the other.

I'm not sure I understand your use case correctly. But maybe check out the Core package readme that contains how to parameterize certain things and pass in information across stacks.

https://docs.aws.amazon.com/cdk/api/latest/docs/core-readme.html

EDIT: you can do something like:

var s1 = new stackOne();
var s2 = new stackTwo().addDependency(s1);

This blog post was helpful for me: https://lanwen.ru/posts/aws-cdk-edge-lambda/

Edit: Some practical examples of sharing resources between stacks. StackA creates a CloudFront distribution (The ID of the distribution is dynamic)

StackB needs the CloudFront distribution Id to set up the alarm.

// stackA
export class CloudFrontStack extends cdk.Stack {
  readonly distribution: cf.CloudFrontWebDistribution;
  constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);
 distribution = new cf.CloudFrontWebDistribution(this, 'my-cloud-front-dist', {//props here...} );
 }
}

// stack B
export class AlarmStack extends cdk.Stack {
constructor(scope: cdk.Construct, id: string, cloudfrontDistributionId: string, props?: cdk.StackProps) {
    super(scope, id, props);   
    new alarm.Alarm()// alarm definition, need ID of CF Distribution here.
 }
}

//index.ts where everything is linked:
const app = new cdk.App();
const stack1= new CloudFrontStack(app, 'CFStack1');
const stack2= new AlarmStack(app, 'AlarmStack', stack1.distribution.distributionId);
// you can even specify that stack2 cannot be created unless stack1 succeeds.
stack2.addDependency(stack1);

EDIT2 : For using resources that have been created after a stack is built and outside of the CDK, the easiest way I can think of is to define CfnOutputs and then query the AWS api using the CLI, either manually or in the CI/CD pipeline if we're automating more things after.

Example2: using the previous example we will define an output called CloudFront-DistributioId and query it using the CLI.

// stackA
export class CloudFrontStack extends cdk.Stack {
  readonly distribution: cf.CloudFrontWebDistribution;
  constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);
 distribution = new cf.CloudFrontWebDistribution(this, 'my-cloud-front-dist', {//props here...} );

// define a cloud formation output so we can query later  
new CfnOutput(this, 'CloudFront-DistributionId', {
  exportName: 'CloudFront-DistributionId',
  value: cloudFrontDistribution.distributionId,
  description: 'The dynamic value created by aws of our CloudFront distribution id. '
});
 }
}

After the stack is created, in the pipeline/cli, use the following command to get the value of the variable:

aws cloudformation describe-stacks --stack-name CloudFrontStack --query "Stacks[0].Outputs[?OutputKey=='CloudFront-DistributionId'].OutputValue"

This will produce the Distribution ID that was created after the stack built.