What outcome occurs when the resource definition of a virtual machine is removed after it has been created and 'terraform apply' is run again?

When the resource definition of a virtual machine is removed and 'terraform apply' is executed, Terraform recognizes that the resource is no longer defined in the configuration files. As a result, Terraform concludes that the resource needs to be removed from the infrastructure. This is grounded in Terraform's intended design, which focuses on aligning the actual state of resources with the desired state specified in configuration files.

In this scenario, Terraform will interpret the absence of the resource definition as an instruction to destroy that virtual machine, ensuring the infrastructure matches the updated configuration. This behavior follows Terraform's principle of managing infrastructure as code, where any drift between the desired and actual state results in changes being applied to the environment.

The other outcomes do not align with Terraform's operational logic in this context. Terraform has mechanisms to manage resources based on the current local state and configuration files, so it will not ignore or report an error regarding the undefined resource. Instead, it actively responds to discrepancies by adjusting the managed infrastructure accordingly.