(ec2): cannot provide availabilityZones to VPC

Describe the bug

I cannot use the availabilityZones prop for VPC without it throwing an error about my stack not being able to use those AZs. I can only use dummy1a etc.

Error message:

Given VPC 'availabilityZones' us-east-1a must be a subset of the stack's availability zones dummy1a,dummy1b,dummy1c

The docs state that:

The number of Availability Zones that are available depends on the region and account of the Stack containing the VPC. If the region and account are specified on the Stack, the CLI will look up the existing Availability Zones and get an accurate count.

However, specifying the environment on the stack will not force a lookup for viable AZs even when supplying AZs to the availabilityZones prop

The described workaround overriding get availabilityZones() works, however that should not be necessary to be able to specify the AZs to use in a new VPC

Expected Behavior

VPC to use supplied AZs

Current Behavior

Throws error because the usable Stack AZs are dummy values

Reproduction Steps

Specify a new VPC

    new Vpc(this, 'vpc', {
      availabilityZones: ['us-east-1a']
    })

In the stack I’ve supplied an account number as well as the region. Interestingly enough, not supplying the environment to the stack will lead to successful synth

Possible Solution

The context lookup is not triggered for Stack.availabilityZones, but it should be triggered in this case, or there should be no check to make sure that the availability zones are valid.

Additional Information/Context

The issue goes away if you specify the availability zones based off the availability zones from the stack

    const vpc = new ec2.Vpc(this, 'TestVPC', {
      cidr: '10.0.0.0/16',
      availabilityZones: cdk.Stack.of(this).availabilityZones.sort().slice(0,1)
    })

This will ensure a lookup occurs

CDK CLI Version

2.38

Framework Version

No response

Node.js Version

.

OS

.

Language

Typescript

Language Version

No response

Other information

No response

[peterwoodworth]

@gumonet you’re right that the context file isn’t getting created, the issue is that this is occurring during synth and no lookup is occurring at all for some reason. If a lookup were actually happening this wouldn’t be an issue, but I and some others have been encountering this issue so there is some inconsistency somewhere which is preventing a lookup from occurring.

@pradoz thanks for looking into this, but I can still reproduce this on latest version. It’s possible you already have the context file in your testing environment

Steps to reproduce:

1. cdk init in new folder
2. Supply environment variables
3. Add env to stack (both explicit and using env variables creates error)
4. Add Vpc to stack

    new Vpc(this, 'vpc', {
      availabilityZones: ['us-east-1a']
    })

1. cdk synth

[karrth]

I was also able to work around by adding this method to the NestedStack that contains the VPC construct (TypeScript):

get availabilityZones() {
  return this.customAvailabilityZones;
}

I set this.customAvailabilityZones in the NestedStack constructor and it seems to work.

This also helped me create VPCs in a nested stack with cross account deploys, where the nested stack was unable to resolve the availability zones in the second account. Adding this function and providing the data from the parent stack as an argument made it work as expected.

I was also able to resolve this problem by manually adding the availability zones for the second account in the context file, but I’d like to avoid that manual step as much as possible