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This should work for you:
```
const server = new aws.ec2.Instance("web-server", {
    // ...
    subnetId: vpc.privateSubnetsIds[0], // reference the subnet created by awsx
});
```

I believe it will always be the first _available_ zone found, but different accounts have different zones.

Not all accounts have an *_a_* to be more specific.

my issue here is that I have an EBS volume in AZ `us-east-1a` that I need to attach to the instance. that's why I used a filter on the subnet collection.

I tried to simplify my example, but what I actually have is:
```
subnets =&gt; subnets.filter(x =&gt; x.subnet.availabilityZone == ebs.availabilityZone)
```

OK, I worked around this by selecting `vpc.privateSubnets[0].subnet.availabilityZone` when configuring the EBS volume AZ