AWS CDK: how do I reference cross-stack resources in same app?

Question

I have an App that has two stacks, both within the same region/account. One of those stacks requires the ARN of a lambda that exists in the other stack. How do I reference this?

// within stackA constructor
public StackA(Construct scope, String id, StackProps props) {

    SingletonFunction myLambda = SingletonFunction.Builder.create(this, "myLambda")
                                                          // some code here
                                                          .build()
    CfnOutput myLambdaArn = CfnOutput.Builder.create(this, "myLambdaArn")
                                              .exportName("myLambdaArn")
                                              .description("ARN of the lambda that I want to use in StackB")
                                              .value(myLambda.getFunctionArn())
                                              .build();

}


App app = new App();

Stack stackA = new StackA(app, "stackA", someAProps);

Stack stackB = new StackB(app, "stackB", someBProps);
stackB.dependsOn(stackA);

How do pass the ARN into StackB?

Answer 1

You can access resources in a different stack, as long as they are in the same account and AWS Region. The following example defines the stack stack1, which defines an Amazon S3 bucket. Then it defines a second stack, stack2, which takes the bucket from stack1 as a constructor property.

// Helper method to build an environment
static Environment makeEnv(String account, String region) {
    return Environment.builder().account(account).region(region)
            .build();
}

App app = new App();

Environment prod = makeEnv("123456789012", "us-east-1");

StackThatProvidesABucket stack1 = new StackThatProvidesABucket(app, "Stack1",
        StackProps.builder().env(prod).build());

// stack2 will take an argument "bucket"
StackThatExpectsABucket stack2 = new StackThatExpectsABucket(app, "Stack,",
        StackProps.builder().env(prod).build(), stack1.getBucket());

Answer 2

Option 1:

pass the data from Stack A to Stack B using the constructor :

You can extend cdk.stack and create a new class that will contain stackA.

In that stack, expose the relevant data you want by using public XXX: string\number (etc) ( See line 2 in the example).

Later, just pass this data into StackB constructor ( you can pass it using props as well).

Working code snippet:

Stack A:

    export class StackA extends cdk.Stack {
        public YourKey: KEY_TYPE;
    
        constructor(scope: cdk.Construct, id: string, props: cdk.StackProps ) {
            super(scope, id, props);
    
            Code goes here...
    
            // Output the key 
            new cdk.CfnOutput(this, 'KEY', { value: this.YourKey });
    
        }
    }

Stack B:

export class StackB extends cdk.Stack {
    constructor(scope: cdk.Construct, id: string,importedKey: KEY_TYPE, props: cdk.props) {
        super(scope, id, props)

        Code goes here...
        
        console.log(importedKey)

    }
}

bin ts:

const importedKey = new StackA(app, 'id',props).YourKey;
new StackB(app, 'id',importedKey,props);

Option 2:

Sometimes it's just better to save this kind of stuff in the parameter store and read it from there.

More info here.

Answer 3

CDK's official documentation has a complete example for sharing a S3 bucket between stacks. I copied it below for quicker reference.

/**
 * Stack that defines the bucket
 */
class Producer extends cdk.Stack {
  public readonly myBucket: s3.Bucket;

  constructor(scope: cdk.App, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const bucket = new s3.Bucket(this, 'MyBucket', {
      removalPolicy: cdk.RemovalPolicy.DESTROY,
    });
    this.myBucket = bucket;
  }
}

interface ConsumerProps extends cdk.StackProps {
  userBucket: s3.IBucket;
}

/**
 * Stack that consumes the bucket
 */
class Consumer extends cdk.Stack {
  constructor(scope: cdk.App, id: string, props: ConsumerProps) {
    super(scope, id, props);

    const user = new iam.User(this, 'MyUser');
    props.userBucket.grantReadWrite(user);
  }
}

const producer = new Producer(app, 'ProducerStack');
new Consumer(app, 'ConsumerStack', { userBucket: producer.myBucket });