RDS errorous use of StorageType by creating DatabaseInstance with engine AURORA_POSTGESQL

[tn0]

I want to create a DBInstance, I do not have set storageType in the DatabaseInstancdeProps.
The deployment stops with an error.

Reproduction Steps

private createDbInstance():DatabaseInstance {
    const props:DatabaseInstanceProps = {
      engine: DatabaseInstanceEngine.AURORA_POSTGRESQL,
      instanceClass: InstanceType.of(InstanceClass.T3, InstanceSize.MEDIUM),
      multiAz: false,
      vpc: this.vpc,
      vpcPlacement: {
        subnetType: SubnetType.PRIVATE
      },
      databaseName: "test",
      masterUsername: "dbuser",
    };
    return new DatabaseInstance(this, "db-instance", props);
  }

Error Log

db-instance (dbinstance310A317F) Invalid storage type: gp2 (Service: AmazonRDS; Status Code: 400; Error Code: StorageTypeNotSupported; Request ID: 94bc0136-a3f8-4bca-9cdf-de8ff9ec3820)
        new DatabaseInstance (/test/node_modules/@aws-cdk/aws-rds/lib/instance.ts:743:22)
        \_ EksTest.createDbInstance (/test/deployment/lib/eks-test.ts:102:16)
        \_ new EksTest (/test/deployment/lib/eks-test.ts:16:32)
        \_ Object.<anonymous> (/test/deployment/bin/eks-test.ts:8:1)
        \_ Module._compile (internal/modules/cjs/loader.js:689:30)
        \_ Module.m._compile (/.npm/_npx/46590/lib/node_modules/ts-node/src/index.ts:536:23)
        \_ Module._extensions..js (internal/modules/cjs/loader.js:700:10)
        \_ Object.require.extensions.(anonymous function) [as .ts] (/.npm/_npx/46590/lib/node_modules/ts-node/src/index.ts:539:12)
        \_ Module.load (internal/modules/cjs/loader.js:599:32)
        \_ tryModuleLoad (internal/modules/cjs/loader.js:538:12)
        \_ Function.Module._load (internal/modules/cjs/loader.js:530:3)
        \_ Function.Module.runMain (internal/modules/cjs/loader.js:742:12)
        \_ main (/npm/_npx/46590/lib/node_modules/ts-node/src/bin.ts:212:14)
        \_ Object.<anonymous> (/.npm/_npx/46590/lib/node_modules/ts-node/src/bin.ts:470:3)
        \_ Module._compile (internal/modules/cjs/loader.js:689:30)
        \_ Object.Module._extensions..js (internal/modules/cjs/loader.js:700:10)
        \_ Module.load (internal/modules/cjs/loader.js:599:32)
        \_ tryModuleLoad (internal/modules/cjs/loader.js:538:12)
        \_ Function.Module._load (internal/modules/cjs/loader.js:530:3)
        \_ Function.Module.runMain (internal/modules/cjs/loader.js:742:12)
        \_ findNodeScript.then.existing (/usr/local/lib/node_modules/npm/node_modules/libnpx/index.js:268:14)

Environment

• **CLI Version :aws-cli/1.16.273 Python/3.7.5 Darwin/18.7.0 botocore/1.13.9
• **Framework Version:*1.18.1
• **OS :Mac OS 10.14.6
• **Language :Typescript

Other

There should no key storageType in DatabasInstanceProps, when engine is AURORA*

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This is 🐛 Bug Report

[jogold]

Aurora instances can only be created inside a cluster. You should use new DatabaseCluster with the Aurora engine.

It's true that the code currently allows this behavior and that it shouldn't.