Question

You are writing Terraform configuration that provisions an AWS EC2 instance which must be attached to a specific subnet. The subnet is created in the same configuration as an aws_subnet resource. You want Terraform to always create the subnet before the instance without adding any extra meta-arguments. What is the recommended way to achieve this ordering?

Accepted Answer

Reference the subnet resource's id attribute (e.g., aws_subnet.main.id) in the instance's subnet_id argument so Terraform infers an implicit dependency.

Answer

Add depends_on = [aws_subnet.main] to the aws_instance resource block to force the ordering.

Answer

Place the aws_subnet block physically above the aws_instance block in the .tf file so it is created first.

Answer

Use a local-exec provisioner on the instance to wait until the subnet exists before continuing.