# Manage machines > See also: [Juju | Machine](https://canonical.com/juju/docs/juju-cli/latest/reference/machine/#machine) ## Reference an externally managed machine To reference a machine that you’ve already provisioned outside of the current Terraform plan, in your Terraform plan add a data source of the `juju_machine` type, specifying the machine ID and the name of its hosting model. For example: ```terraform data "juju_machine" "this" { model_uuid = juju_model.development.uuid machine_id = "2" } ``` > See more: [`juju_machine` (data source)](https://documentation.ubuntu.com/terraform-provider-juju/latest/reference/terraform-provider/data-sources/machine.md) ## Add a machine To add a machine to a model, in your Terraform plan add a resource of the `juju_machine` type, specifying the model. ```terraform resource "juju_machine" "machine_0" { model_uuid = juju_model.development.uuid } ``` You can optionally specify a base, a name, regular constraints, storage constraints, etc. You can also specify a `private_key_file`, `public_key_file`, and `ssh_address` – that will allow you to add to the model an existing, manual machine (rather than a virtual one provisioned for you by the cloud). > See more: [`juju_machine` (resource)](https://documentation.ubuntu.com/terraform-provider-juju/latest/reference/terraform-provider/resources/machine.md) ## Manage constraints for a machine > See also: [Juju | Constraint](https://canonical.com/juju/docs/juju-cli/latest/reference/constraint/#constraint) To set constraints for a machine, in your Terraform plan, in the machine resource definition, set the constraints attribute to the desired quotes-enclosed, space separated list of key=value pairs. For example: ```terraform resource "juju_machine" "machine_0" { model_uuid = juju_model.development.uuid name = "machine_0" constraints = "tags=my-machine-tag" } ``` > See more: [`juju_machine` (resource)](https://documentation.ubuntu.com/terraform-provider-juju/latest/reference/terraform-provider/resources/machine.md) ## Remove a machine > See also: [Juju | Removing things](https://canonical.com/juju/docs/juju-cli/latest/reference/removing-things/#removing-things) To remove a machine, remove its resource definition from your Terraform plan. > See more: [`juju_machine` (resource)](https://documentation.ubuntu.com/terraform-provider-juju/latest/reference/terraform-provider/resources/machine.md)