cdk/lib/external_parameters.ts

import type { GuStack } from '@guardian/cdk/lib/constructs/core';
import { aws_ssm } from 'aws-cdk-lib';
import type { IStringParameter } from 'aws-cdk-lib/aws-ssm';
import { Construct } from 'constructs';

/**
 * ExternalParameters encapsulates values that are not specific to this stack, i.e. are set by other stacks or
 * are properties of the account setup itself.
 *
 * The CDK formulation here actually creates a Cloudformation parameter, whose default value is then obtained from
 * SSM _at deploy time_.  Therefore, the values that are used for these will be that of the SSM parameter value at the
 * time of deployment rather than the time at which the stack was built.
 */
export class ExternalParameters extends Construct {
	urgentAlarmTopicArn: IStringParameter;
	nonUrgentAlarmTopicArn: IStringParameter;

	constructor(scope: GuStack, id: string) {
		super(scope, id);

		this.urgentAlarmTopicArn = aws_ssm.StringParameter.fromStringParameterName(
			this,
			'urgent-alarm-arn',
			'/account/services/alarms/urgent-alarm-topic',
		);
		this.nonUrgentAlarmTopicArn =
			aws_ssm.StringParameter.fromStringParameterName(
				this,
				'non-urgent-alarm-arn',
				'/account/services/alarms/non-urgent-alarm-topic',
			);
	}
}