The provisioners section, which is optional, contains a list of scripts that will be executed by Packer on a temporary VM base image in order to build our custom VM image according to our needs.

If the Packer template does not contain a provisioners section, no configuration will be made on the base images.

The actions defined in this section are available for Windows as well as Linux images, and the actions be of several types such as executing a local or remote script, executing a command, or copying a file.

It is also possible to extend Packer by creating custom provisioning types. To learn more about custom provisioners, refer to the documentation here: https://www.packer.io/docs/extending/custom-provisioners.html.

The following is a sample of a provisioners section:

{
...
    "provisioners": [
        {
         "type": "shell",
         "script": "hardening-config.sh"
        },
        {
         "type": "file",
         "source": "scripts/installers",
         "destination": "/tmp/scripts"
        }
    ]
...
}

In this provisioners section, Packer will upload and execute the local script, hardening-config.sh, to apply the hardening configuration on the remote temporary VM base image, and copy the content of the scripts/installers local folder to the remote folder, /tmp/scripts, to configure the image.

So, in this section, we list all of the configuration actions for the image to be created.

However, when creating an image of a VM, it's necessary to generalize it—in other words, delete all of the personal user information that was used to create this image.

For example, for a Windows VM image, we will use the Sysprep tool as the last step of provisioners with this following code:

"provisioners": [
...
{
 "type": "powershell",
 "inline": ["& C:\windows\System32\Sysprep\Sysprep.exe /oobe /generalize /shutdown /quiet"]}
]

Another example of Sysprep usage in Packer templates is available here: https://www.packer.io/docs/builders/azure.html.

And for deleting the personal user information on a Linux image, we will use the following code:

"provisioners": [
.....
{
  "type": "shell",
  "execute_command": "sudo sh -c '{{ .Vars }} {{ .Path }}'",
  "inline": [
     "/usr/sbin/waagent -force -deprovision+user && export HISTSIZE=0 && sync"
  ]
 }
]

After the provisioners section, let's talk about variables.