export() must be idempotent (was: error when calling export() on multiple items)

[BDQ]

The Stack code below results in the following error:

Error: There is already a Construct with name 'PublicSubnetIDs' in VpcNetwork

export class ClusterStack extends cdk.Stack {
  public readonly vpcRefProps: ec2.VpcNetworkRefProps;
  public readonly ecsClusterRefProps: ecs.ImportedClusterProps;

  constructor(parent: cdk.App, name: string) {
    super(parent, name);

    // VPC using a small CIDR for staging
    const vpc = new ec2.VpcNetwork(this, "vpc", {
      cidr: "10.0.0.0/24",
      maxAZs: 2
    });

    // Create the ECS cluster
    const cluster = new ecs.Cluster(this, "cluster", {
      vpc
    });

    // export vpc
    this.vpcRefProps = vpc.export();
    // export cluster
    this.ecsClusterRefProps = cluster.export();
  }
}

[rix0rrr]

Related to:

#1095
#89 (indirectly)

[eladb]

The issue here is vpc.export() is called twice: once explicitly in the code and then implicitly as a result of cluster.export(). And our current pattern for implementing those exports is that we always define a set of new cdk.Outputs for each attribute that we wish to export.

Naturally these outputs can be reused if they are already defined.

Since this is implemented across our entire library, we can probably use some sugar methods so that implementing exports will not be a pain everywhere.

I'll rename the issue to reflect this requirement.

[rix0rrr]

export() no longer exists.