306 lines
14 KiB
Markdown
306 lines
14 KiB
Markdown
---
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layout: "language"
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page_title: "Provisioners"
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sidebar_current: "docs-provisioners"
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description: |-
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Using provisioners in Terraform to execute scripts on a local or remote machine as part of resource creation or destruction.
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---
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# Provisioners
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Provisioners can be used to model specific actions on the local machine or on
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a remote machine in order to prepare servers or other infrastructure objects
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for service.
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## Provisioners are a Last Resort
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> **Hands-on:** To learn about more declarative ways to handle provisioning actions, try the [Provision Infrastructure Deployed with Terraform](https://learn.hashicorp.com/collections/terraform/provision?utm_source=WEBSITE&utm_medium=WEB_IO&utm_offer=ARTICLE_PAGE&utm_content=DOCS) collection on HashiCorp Learn.
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Terraform includes the concept of provisioners as a measure of pragmatism,
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knowing that there will always be certain behaviors that can't be directly
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represented in Terraform's declarative model.
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However, they also add a considerable amount of complexity and uncertainty to
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Terraform usage. Firstly, Terraform cannot model the actions of provisioners
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as part of a plan because they can in principle take any action. Secondly,
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successful use of provisioners requires coordinating many more details than
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Terraform usage usually requires: direct network access to your servers,
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issuing Terraform credentials to log in, making sure that all of the necessary
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external software is installed, etc.
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The following sections describe some situations which can be solved with
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provisioners in principle, but where better solutions are also available. We do
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not recommend using provisioners for any of the use-cases described in the
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following sections.
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Even if your specific use-case is not described in the following sections, we
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still recommend attempting to solve it using other techniques first, and use
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provisioners only if there is no other option.
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### Passing data into virtual machines and other compute resources
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When deploying virtual machines or other similar compute resources, we often
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need to pass in data about other related infrastructure that the software on
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that server will need to do its job.
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The various provisioners that interact with remote servers over SSH or WinRM
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can potentially be used to pass such data by logging in to the server and
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providing it directly, but most cloud computing platforms provide mechanisms
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to pass data to instances at the time of their creation such that the data
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is immediately available on system boot. For example:
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* Alibaba Cloud: `user_data` on
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[`alicloud_instance`](https://registry.terraform.io/providers/aliyun/alicloud/latest/docs/resources/instance)
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or [`alicloud_launch_template`](https://registry.terraform.io/providers/aliyun/alicloud/latest/docs/resources/launch_template).
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* Amazon EC2: `user_data` or `user_data_base64` on
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[`aws_instance`](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/instance),
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[`aws_launch_template`](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/launch_template),
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and [`aws_launch_configuration`](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/launch_configuration).
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* Amazon Lightsail: `user_data` on
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[`aws_lightsail_instance`](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/lightsail_instance).
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* Microsoft Azure: `custom_data` on
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[`azurerm_virtual_machine`](https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/virtual_machine)
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or [`azurerm_virtual_machine_scale_set`](https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/virtual_machine_scale_set).
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* Google Cloud Platform: `metadata` on
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[`google_compute_instance`](https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/compute_instance)
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or [`google_compute_instance_group`](https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/compute_instance_group).
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* Oracle Cloud Infrastructure: `metadata` or `extended_metadata` on
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[`oci_core_instance`](https://registry.terraform.io/providers/hashicorp/oci/latest/docs/resources/core_instance)
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or [`oci_core_instance_configuration`](https://registry.terraform.io/providers/hashicorp/oci/latest/docs/resources/core_instance_configuration).
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* VMware vSphere: Attach a virtual CDROM to
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[`vsphere_virtual_machine`](https://registry.terraform.io/providers/hashicorp/vsphere/latest/docs/resources/virtual_machine)
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using the `cdrom` block, containing a file called `user-data.txt`.
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Many official Linux distribution disk images include software called
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[cloud-init](https://cloudinit.readthedocs.io/en/latest/) that can automatically
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process in various ways data passed via the means described above, allowing
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you to run arbitrary scripts and do basic system configuration immediately
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during the boot process and without the need to access the machine over SSH.
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> **Hands-on:** Try the [Provision Infrastructure with Cloud-Init](https://learn.hashicorp.com/tutorials/terraform/cloud-init?in=terraform/provision&utm_source=WEBSITE&utm_medium=WEB_IO&utm_offer=ARTICLE_PAGE&utm_content=DOCS) tutorial on HashiCorp Learn.
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If you are building custom machine images, you can make use of the "user data"
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or "metadata" passed by the above means in whatever way makes sense to your
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application, by referring to your vendor's documentation on how to access the
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data at runtime.
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This approach is _required_ if you intend to use any mechanism in your cloud
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provider for automatically launching and destroying servers in a group,
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because in that case individual servers will launch unattended while Terraform
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is not around to provision them.
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Even if you're deploying individual servers directly with Terraform, passing
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data this way will allow faster boot times and simplify deployment by avoiding
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the need for direct network access from Terraform to the new server and for
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remote access credentials to be provided.
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### Running configuration management software
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As a convenience to users who are forced to use generic operating system
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distribution images, Terraform includes a number of specialized provisioners
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for launching specific configuration management products.
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We strongly recommend not using these, and instead running system configuration
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steps during a custom image build process. For example,
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[HashiCorp Packer](https://www.packer.io/) offers a similar complement of
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configuration management provisioners and can run their installation steps
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during a separate build process, before creating a system disk image that you
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can deploy many times.
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> **Hands-on:** Try the [Provision Infrastructure with Packer](https://learn.hashicorp.com/tutorials/terraform/packer?in=terraform/provision&utm_source=WEBSITE&utm_medium=WEB_IO&utm_offer=ARTICLE_PAGE&utm_content=DOCS) tutorial on HashiCorp Learn.
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If you are using configuration management software that has a centralized server
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component, you will need to delay the _registration_ step until the final
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system is booted from your custom image. To achieve that, use one of the
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mechanisms described above to pass the necessary information into each instance
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so that it can register itself with the configuration management server
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immediately on boot, without the need to accept commands from Terraform over
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SSH or WinRM.
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### First-class Terraform provider functionality may be available
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It is technically possible to use the `local-exec` provisioner to run the CLI
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for your target system in order to create, update, or otherwise interact with
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remote objects in that system.
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If you are trying to use a new feature of the remote system that isn't yet
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supported in its Terraform provider, that might be the only option. However,
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if there _is_ provider support for the feature you intend to use, prefer to
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use that provider functionality rather than a provisioner so that Terraform
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can be fully aware of the object and properly manage ongoing changes to it.
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Even if the functionality you need is not available in a provider today, we
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suggest to consider `local-exec` usage a temporary workaround and to also
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open an issue in the relevant provider's repository to discuss adding
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first-class provider support. Provider development teams often prioritize
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features based on interest, so opening an issue is a way to record your
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interest in the feature.
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Provisioners are used to execute scripts on a local or remote machine
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as part of resource creation or destruction. Provisioners can be used to
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bootstrap a resource, cleanup before destroy, run configuration management, etc.
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## How to use Provisioners
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-> **Note:** Provisioners should only be used as a last resort. For most
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common situations there are better alternatives. For more information, see
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the sections above.
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If you are certain that provisioners are the best way to solve your problem
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after considering the advice in the sections above, you can add a
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`provisioner` block inside the `resource` block of a compute instance.
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```hcl
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resource "aws_instance" "web" {
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# ...
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provisioner "local-exec" {
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command = "echo The server's IP address is ${self.private_ip}"
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}
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}
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```
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The `local-exec` provisioner requires no other configuration, but most other
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provisioners must connect to the remote system using SSH or WinRM.
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You must include [a `connection` block](./connection.html) so that Terraform
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will know how to communicate with the server.
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Terraform includes several built-in provisioners; use the navigation sidebar to
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view their documentation.
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It's also possible to use third-party provisioners as plugins, by placing them
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in `%APPDATA%\terraform.d\plugins`, `~/.terraform.d/plugins`, or the same
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directory where the Terraform binary is installed. However, we do not recommend
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using any provisioners except the built-in `file`, `local-exec`, and
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`remote-exec` provisioners.
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All provisioners support the `when` and `on_failure` meta-arguments, which
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are described below (see [Destroy-Time Provisioners](#destroy-time-provisioners)
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and [Failure Behavior](#failure-behavior)).
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### The `self` Object
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Expressions in `provisioner` blocks cannot refer to their parent resource by
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name. Instead, they can use the special `self` object.
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The `self` object represents the provisioner's parent resource, and has all of
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that resource's attributes. For example, use `self.public_ip` to reference an
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`aws_instance`'s `public_ip` attribute.
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-> **Technical note:** Resource references are restricted here because
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references create dependencies. Referring to a resource by name within its own
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block would create a dependency cycle.
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## Suppressing Provisioner Logs in CLI Output
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The configuration for a `provisioner` block may use sensitive values, such as
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[`sensitive` variables](/docs/language/values/variables.html#suppressing-values-in-cli-output) or
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[`sensitive` output values](/docs/language/values/outputs.html#sensitive-suppressing-values-in-cli-output).
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In this case, all log output from the provisioner is automatically suppressed to
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prevent the sensitive values from being displayed.
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## Creation-Time Provisioners
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By default, provisioners run when the resource they are defined within is
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created. Creation-time provisioners are only run during _creation_, not
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during updating or any other lifecycle. They are meant as a means to perform
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bootstrapping of a system.
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If a creation-time provisioner fails, the resource is marked as **tainted**.
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A tainted resource will be planned for destruction and recreation upon the
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next `terraform apply`. Terraform does this because a failed provisioner
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can leave a resource in a semi-configured state. Because Terraform cannot
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reason about what the provisioner does, the only way to ensure proper creation
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of a resource is to recreate it. This is tainting.
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You can change this behavior by setting the `on_failure` attribute,
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which is covered in detail below.
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## Destroy-Time Provisioners
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If `when = destroy` is specified, the provisioner will run when the
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resource it is defined within is _destroyed_.
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```hcl
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resource "aws_instance" "web" {
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# ...
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provisioner "local-exec" {
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when = destroy
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command = "echo 'Destroy-time provisioner'"
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}
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}
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```
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Destroy provisioners are run before the resource is destroyed. If they
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fail, Terraform will error and rerun the provisioners again on the next
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`terraform apply`. Due to this behavior, care should be taken for destroy
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provisioners to be safe to run multiple times.
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Destroy-time provisioners can only run if they remain in the configuration
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at the time a resource is destroyed. If a resource block with a destroy-time
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provisioner is removed entirely from the configuration, its provisioner
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configurations are removed along with it and thus the destroy provisioner
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won't run. To work around this, a multi-step process can be used to safely
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remove a resource with a destroy-time provisioner:
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* Update the resource configuration to include `count = 0`.
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* Apply the configuration to destroy any existing instances of the resource, including running the destroy provisioner.
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* Remove the resource block entirely from configuration, along with its `provisioner` blocks.
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* Apply again, at which point no further action should be taken since the resources were already destroyed.
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This limitation may be addressed in future versions of Terraform. For now,
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destroy-time provisioners must be used sparingly and with care.
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~> **NOTE:** A destroy-time provisioner within a resource that is tainted _will not_ run. This includes resources that are marked tainted from a failed creation-time provisioner or tainted manually using `terraform taint`.
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## Multiple Provisioners
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Multiple provisioners can be specified within a resource. Multiple provisioners
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are executed in the order they're defined in the configuration file.
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You may also mix and match creation and destruction provisioners. Only
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the provisioners that are valid for a given operation will be run. Those
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valid provisioners will be run in the order they're defined in the configuration
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file.
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Example of multiple provisioners:
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```hcl
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resource "aws_instance" "web" {
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# ...
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provisioner "local-exec" {
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command = "echo first"
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}
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provisioner "local-exec" {
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command = "echo second"
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}
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}
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```
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## Failure Behavior
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By default, provisioners that fail will also cause the Terraform apply
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itself to fail. The `on_failure` setting can be used to change this. The
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allowed values are:
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- `continue` - Ignore the error and continue with creation or destruction.
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- `fail` - Raise an error and stop applying (the default behavior). If this is a creation provisioner,
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taint the resource.
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Example:
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```hcl
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resource "aws_instance" "web" {
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# ...
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provisioner "local-exec" {
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command = "echo The server's IP address is ${self.private_ip}"
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on_failure = continue
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}
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}
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```
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