Cloud Site creation fails due to a "Resource CREATE failed: invalid availability zone" error
Challenge
Cloud Site fails to launch and returns a similar error message:
"Error launching cloudsite <ID> for customer <Name> Creation failed: Stack <ID> went to status CREATE_FAILED due to: Resource CREATE failed: ClientError: resources.WIN-H06N: An error occurred (InvalidParameterValue) when calling the RunInstances operation: Value (us-east-1b) for parameter availabilityZone is invalid. Subnet 'subnet-name' is in the availability zone us-east-1a"
Cause
Cloud Site parameters have been set up to launch instances in a certain Availability Zone ("us-east-1b" as in the example above) while using an inapplicable subnet ID from another AZ (e.g. "us-east-1a").
Solution
When creating a DR/Migration Plan, make sure to check that the specified subnet ID belongs to the actual Availability Zone.