As mentioned in the comments, if you're happy to spin up a different type of instance if the preferred type isn't available then you can use the aws_ec2_instance_type_offering data source to instead fallback to the t2 instance family in the affected availability zone.
The following Terraform code will output a map of availability zones to the instance type allowed, preferring t3.micro but falling back to t2.micros where the t3 family isn't available:
provider "aws" {
region = "us-east-1"
}
data "aws_availability_zones" "all" {}
data "aws_ec2_instance_type_offering" "example" {
for_each = toset(data.aws_availability_zones.all.names)
filter {
name = "instance-type"
values = ["t2.micro", "t3.micro"]
}
filter {
name = "location"
values = [each.value]
}
location_type = "availability-zone"
preferred_instance_types = ["t3.micro", "t2.micro"]
}
output "foo" {
value = { for az, details in data.aws_ec2_instance_type_offering.example : az => details.instance_type }
}
This outputs:
foo = {
"us-east-1a" = "t3.micro"
"us-east-1b" = "t3.micro"
"us-east-1c" = "t3.micro"
"us-east-1d" = "t3.micro"
"us-east-1e" = "t2.micro"
"us-east-1f" = "t3.micro"
}
Instead of just outputting this you should be able to iterate over the availability zones to set the instance type for the aws_instance resource.
Alternatively you could filter the output to reduce it to just a list of the AZs that can offer the t3 instance family by changing the output to the following:
output "foo" {
value = keys({ for az, details in data.aws_ec2_instance_type_offering.example : az => details.instance_type if details.instance_type == "t3.micro" })
}
This outputs the following, skipping the availability zone that doesn't include the t3 instance family:
foo = [
"us-east-1a",
"us-east-1b",
"us-east-1c",
"us-east-1d",
"us-east-1f",
]
