Vpc.fromVpcAttributes throws Validation exception from ec2 construct

When I import an existing VPC using this

const vpc = ec2.Vpc.fromVpcAttributes(this, 'Vpc', {
      vpcId: cdk.Fn.importValue('VPC'),
      availabilityZones: cdk.Fn.getAzs(),
      privateSubnetIds: [1, 2, 3].map(i => cdk.Fn.importValue(`PrivateSubnet0${i}`)),
      publicSubnetIds: [1, 2, 3].map(i => cdk.Fn.importValue(`PublicSubnet0${i}`))
});

I get the following error while synthesis:

There is already a Construct with name 'undefinedSubnet2' in ImportedVpc [Vpc]

/node_modules/@aws-cdk/core/lib/construct.ts:48
        throw new Error(`Validation failed with the following errors:\n  ${errorList}`);
              ^

What is the correct way to resolve this problem?

Reproduction Steps

Error Log

Environment

• **CLI Version :1.22.0
• **Framework Version:1.23.0
• OS :
• **Language :TS

Other

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This is 🐛 Bug Report

[ayush987goyal]

Hi,

I tried the above implementation but I am not getting another error related to the same:

Cannot determine scope for context provider hosted-zone.
This usually happens when one or more of the provider props have unresolved tokens

The current implementation I have is

const vpc = ec2.Vpc.fromVpcAttributes(this, 'Vpc', {
      vpcId: cdk.Fn.importValue('VPC'),
      availabilityZones: [0, 1, 2].map(i => cdk.Fn.select(i, cdk.Fn.getAzs('us-east-1'))),
      privateSubnetIds: [1, 2, 3].map(i => cdk.Fn.importValue(`PrivateSubnet0${i}`)),
      publicSubnetIds: [1, 2, 3].map(i => cdk.Fn.importValue(`PublicSubnet0${i}`))
});

[rix0rrr]

Fairly sure that this has nothing to do with your VPC, given that the error message says “context provider hosted-zone”. You are probably doing HostedZone.fromLookup(Fn.importValue(...)) or similar.

That won’t work because fromLookup() is evaluated by CDK and Fn.importValue() is evaluated by CFN (which happens later in time, so fromLookup() can never use the actual value CFN would have imported).

See here for an explanation: https://docs.aws.amazon.com/cdk/latest/guide/apps.html#lifecycle

You need concrete parameters, not Fn.importValues().