feat(rds): add clusterArn property to DatabaseCluster

[blimmer]

Reason for this change

It wasn't clear to me how to get the clusterArn from DatabaseCluster. This PR adds that property.

Description of changes

Add clusterArn to DatabaseCluster, just like ServerlessCluster exposes.

Description of how you validated changes

Added unit test similar to ServerlessCluster.

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

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[blimmer]

Just like ServerlessCluster

aws-cdk/packages/aws-cdk-lib/aws-rds/lib/serverless-cluster.ts

Lines 345 to 355 in 1f30b5d

	/**
	* The ARN of the cluster
	*/
	public get clusterArn(): string {
	return Stack.of(this).formatArn({
	service: 'rds',
	resource: 'cluster',
	arnFormat: ArnFormat.COLON_RESOURCE_NAME,
	resourceName: this.clusterIdentifier,
	});
	}

[jfuss]

@blimmer Is this how CDK normally handles this? I ask because the output becomes a Join instead of doing a GetAtt on the resource. Trying to wrap my head around why we should do this over the GetAtt path. I tried looking at the Lambda Function L2, since there is a readonly property for the Arn.

Honestly not sure if it matters (likely not) but trying to learn different parts of this as I go. To me seems like we have two patterns going on, the one you have here and the readonly property for the Arn.

[blimmer]

I'm not sure - I just followed the pattern in the linked code. One of the core contributors might be able to tell us.

[jfuss]

I asked the team directly. I did find SQS which does this differently. https://github.com/aws/aws-cdk/blob/v2.130.0/packages/aws-cdk-lib/aws-sqs/lib/queue.ts#L437-L440

const queue = new sqs.Queue(this, 'CdkExampleQueue', {
      visibilityTimeout: Duration.seconds(300)
    });

new CfnOutput(this, "arn", {
      exportName: "arn",
      value: queue.queueArn,
    })

CFN Synth

Outputs:
  arn:
    Value:
      Fn::GetAtt:
        - CdkExampleQueue7618E31B
        - Arn
    Export:
      Name: arn

Which fits my mental model better. I am not sure if there is a big difference or a reason it was done this way in RDS. Maybe one is a "legacy" way of doing things.

Generally, this looks fine. I just want to get some deeper clarity on what is typical.

[colifran]

@jfuss Sorry to jump in - I was looking at something similar recently. This is a very typical pattern that is used in the codebase here are just a few examples:

aws-cdk/packages/aws-cdk-lib/aws-kms/lib/alias.ts

Line 69 in 0d6ef63

return Stack.of(this).formatArn({

aws-cdk/packages/aws-cdk-lib/aws-docdb/lib/instance.ts

Line 103 in 0d6ef63

return cdk.Stack.of(this).formatArn({

aws-cdk/packages/aws-cdk-lib/aws-apigateway/lib/stage.ts

Line 260 in 0d6ef63

return Stack.of(this).formatArn({

Also, this is just a "getter" for the clusterArn so I don't think we want to be producing any outputs in the synthesized template. Instead, this just allows clusterArn to be exposed for use throughout the rest of their app.

[blimmer]

aws-cdk/packages/aws-cdk-lib/aws-rds/test/serverless-cluster.test.ts

Lines 602 to 627 in 1f30b5d

	test('check that clusterArn property works', () => {
	// GIVEN
	const stack = testStack();
	const vpc = ec2.Vpc.fromLookup(stack, 'VPC', { isDefault: true });
	const cluster = new ServerlessCluster(stack, 'Database', {
	engine: DatabaseClusterEngine.AURORA_MYSQL,
	vpc,
	});
	const exportName = 'DbCluterArn';
	// WHEN
	new cdk.CfnOutput(stack, exportName, {
	exportName,
	value: cluster.clusterArn,
	});
	// THEN
	expect(stack.resolve(cluster.clusterArn)).toEqual({
	'Fn::Join': ['', [
	'arn:',
	{ Ref: 'AWS::Partition' },
	':rds:us-test-1:12345:cluster:',
	{ Ref: 'DatabaseB269D8BB' },
	]],
	});
	});

[blimmer]

Exemption request. The JSDoc should be sufficient and I added a unit test.

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[go-to-k]

Is there a duplication with this PR?

#29133

[jfuss]

@blimmer Thanks for spending the time. I missed there was another PR already for this and was merged yesterday: #29133.

Closing this as it is a duplicate