Terraform not only helps us in infrastructure creation and management but also in provisioning them during resource creation or deletion.

Provisioners are used to execute scripts or shell commands on a local or remote machine as part of resource creation or deletion.

Provisioners can be used to bootstrap a resource, cleanup before destroy, run configuration management etc.

Below are list of the supported provisioners

• chef : The chef provisioner installs, configures and runs the Chef Client on a remote resource.
• connection : The chef provisioner to define or override connection properties of a resource
• file : The file provisioner is used to copy files or directories to the newly created resource.
• habitat : The habitat provisioner installs the Habitat supervisor and loads configured services.
• local-exec : The local-exec provisioner invokes a local executable after a resource is created.
• null_resource : The null_resource is a resource that allows you to configure provisioners that are not directly associated with a single existing resource.
• remote-exec : The remote-exec provisioner invokes a script on a remote resource after it is created.
• salt-masterless : The salt-masterless Terraform provisioner provisions machines built by Terraform using Salt states, without connecting to a Salt master.

Defining a Provisioner

To define a provisioner, add a provisioner block within the resource block. Multiple provisioner blocks can be added to define multiple provisioning steps.

resource "aws_instance" "webserver" {
  ami = "ami-b374d5a5"
  instance_type = "t2.micro"

  provisioner "local-exec" {
  command = "echo ${aws_instance.webserver.public_ip} > ip_address.txt"
  }
}

Running Provisioners

Provisioners by default run only when a resource is created, not during updating or any other lifecycle.

If a creation-time provisioner fails, the resource is marked as tainted. A tainted resource will be planned for deletion and recreation upon the next terraform apply.

Failure Behavior

By default, provisioners that fail will cause to error. With on_failure setting we can change this.

The allowed values are:

• continue : Ignore the error and continue with creation or destruction.
• fail (default behavior): Error. If it is a creation provisioner, taint the resource.

resource "aws_instance" "webserver" {
# ...

  provisioner "local-exec" {
  command = "echo ${server.private_ip} > file.txt"
  on_failure = "continue"
 }
}

 

Destroy Provisioners

Provisioners can also be defined that run only during a destroy operation. These are useful for performing system cleanup, extracting data, etc.

If when = “destroy” is specified, the provisioner will before the resource is destroyed.

resource "aws_instance" "web" {
# ...
  provisioner "local-exec" {
    command = "echo Creating"
  }
  provisioner "local-exec" {
    when = "destroy"
    command = "echo Destroying"
  }
}