» PowerShell Provisioner

Type: powershell

The PowerShell Packer provisioner runs PowerShell scripts on Windows machines. It assumes that the communicator in use is WinRM. However, the provisioner can work equally well (with a few caveats) when combined with the SSH communicator. See the section below for details.

» Basic Example

The example below is fully functional.

{
  "type": "powershell",
  "inline": ["dir c:\\"]
}

» Configuration Reference

The reference of available configuration options is listed below. The only required element is either "inline" or "script". Every other option is optional.

Exactly one of the following is required:

  • inline (array of strings) - This is an array of commands to execute. The commands are concatenated by newlines and turned into a single file, so they are all executed within the same context. This allows you to change directories in one command and use something in the directory in the next and so on. Inline scripts are the easiest way to pull off simple tasks within the machine.

  • script (string) - The path to a script to upload and execute in the machine. This path can be absolute or relative. If it is relative, it is relative to the working directory when Packer is executed.

  • scripts (array of strings) - An array of scripts to execute. The scripts will be uploaded and executed in the order specified. Each script is executed in isolation, so state such as variables from one script won't carry on to the next.

Optional parameters:

  • binary (boolean) - If true, specifies that the script(s) are binary files, and Packer should therefore not convert Windows line endings to Unix line endings (if there are any). By default this is false.

  • elevated_execute_command (string) - The command to use to execute the elevated script. By default this is as follows:

    powershell -executionpolicy bypass "& { if (Test-Path variable:global:ProgressPreference){$ProgressPreference='SilentlyContinue'};. {{.Vars}}; &'{{.Path}}'; exit $LastExitCode }"
    

    The value of this is treated as configuration template. There are two available variables: Path, which is the path to the script to run, and Vars, which is the location of a temp file containing the list of environment_vars, if configured.

  • environment_vars (array of strings) - An array of key/value pairs to inject prior to the execute_command. The format should be key=value. Packer injects some environmental variables by default into the environment, as well, which are covered in the section below. If you are running on AWS, Azure or Google Compute and would like to access the generated password that Packer uses to connect to the instance via WinRM, you can use the template variable {{.WinRMPassword}} to set this as an environment variable. For example:

      {
        "type": "powershell",
        "environment_vars": "WINRMPASS={{.WinRMPassword}}",
        "inline": ["Write-Host \"Automatically generated aws password is: $Env:WINRMPASS\""]
      },
    
  • execute_command (string) - The command to use to execute the script. By default this is as follows:

    powershell -executionpolicy bypass "& { if (Test-Path variable:global:ProgressPreference){$ProgressPreference='SilentlyContinue'};. {{.Vars}}; &'{{.Path}}'; exit $LastExitCode }"
    

    The value of this is treated as configuration template. There are two available variables: Path, which is the path to the script to run, and Vars, which is the location of a temp file containing the list of environment_vars. The value of both Path and Vars can be manually configured by setting the values for remote_path and remote_env_var_path respectively.

    If you use the SSH communicator and have changed your default shell, you may need to modify your execute_command to make sure that the command is valid and properly escaped; the default assumes that you have not changed the default shell away from cmd.

  • elevated_user and elevated_password (string) - If specified, the PowerShell script will be run with elevated privileges using the given Windows user. If you are running a build on AWS, Azure or Google Compute and would like to run using the generated password that Packer uses to connect to the instance via WinRM, you may do so by using the template variable {{.WinRMPassword}}. For example:

    "elevated_user": "Administrator",
    "elevated_password": "{{.WinRMPassword}}",
    

    If you specify an empty elevated_password value then the PowerShell script is run as a service account. For example:

    "elevated_user": "SYSTEM",
    "elevated_password": "",
    
  • remote_path (string) - The path where the PowerShell script will be uploaded to within the target build machine. This defaults to C:/Windows/Temp/script-UUID.ps1 where UUID is replaced with a dynamically generated string that uniquely identifies the script.

    This setting allows users to override the default upload location. The value must be a writable location and any parent directories must already exist.

  • remote_env_var_path (string) - Environment variables required within the remote environment are uploaded within a PowerShell script and then enabled by 'dot sourcing' the script immediately prior to execution of the main command or script.

    The path the environment variables script will be uploaded to defaults to C:/Windows/Temp/packer-ps-env-vars-UUID.ps1 where UUID is replaced with a dynamically generated string that uniquely identifies the script.

    This setting allows users to override the location the environment variable script is uploaded to. The value must be a writable location and any parent directories must already exist.

  • start_retry_timeout (string) - The amount of time to attempt to start the remote process. By default this is "5m" or 5 minutes. This setting exists in order to deal with times when SSH may restart, such as a system reboot. Set this to a higher value if reboots take a longer amount of time.

  • valid_exit_codes (list of ints) - Valid exit codes for the script. By default this is just 0.

» Default Environmental Variables

In addition to being able to specify custom environmental variables using the environment_vars configuration, the provisioner automatically defines certain commonly useful environmental variables:

  • PACKER_BUILD_NAME is set to the name of the build that Packer is running. This is most useful when Packer is making multiple builds and you want to distinguish them slightly from a common provisioning script.

  • PACKER_BUILDER_TYPE is the type of the builder that was used to create the machine that the script is running on. This is useful if you want to run only certain parts of the script on systems built with certain builders.

  • PACKER_HTTP_ADDR If using a builder that provides an http server for file transfer (such as hyperv, parallels, qemu, virtualbox, and vmware), this will be set to the address. You can use this address in your provisioner to download large files over http. This may be useful if you're experiencing slower speeds using the default file provisioner. A file provisioner using the winrm communicator may experience these types of difficulties.

» Combining the PowerShell Provisioner with the SSH Communicator

The good news first. If you are using the Microsoft port of OpenSSH then the provisioner should just work as expected - no extra configuration effort is required.

Now the caveats. If you are using an alternative configuration, and your SSH connection lands you in a *nix shell on the remote host, then you will most likely need to manually set the execute_command; The default execute_command used by Packer will not work for you. When configuring the command you will need to ensure that any dollar signs or other characters that may be incorrectly interpreted by the remote shell are escaped accordingly.

The following example shows how the standard execute_command can be reconfigured to work on a remote system with Cygwin/OpenSSH installed. The execute_command has each dollar sign backslash escaped so that it is not interpreted by the remote Bash shell - Bash being the default shell for Cygwin environments.

  "provisioners": [
    {
      "type": "powershell",
      "execute_command": "powershell -executionpolicy bypass \"& { if (Test-Path variable:global:ProgressPreference){\\$ProgressPreference='SilentlyContinue'};. {{.Vars}}; &'{{.Path}}'; exit \\$LastExitCode }\"",
      "inline": [
        "Write-Host \"Hello from PowerShell\"",
      ]
    }
  ]

» Packer's Handling of Characters Special to PowerShell

The escape character in PowerShell is the backtick, also sometimes referred to as the grave accent. When, and when not, to escape characters special to PowerShell is probably best demonstrated with a series of examples.

» When To Escape...

Users need to deal with escaping characters special to PowerShell when they appear directly in commands used in the inline PowerShell provisioner and when they appear directly in the users own scripts. Note that where double quotes appear within double quotes, the addition of a backslash escape is required for the JSON template to be parsed correctly.

  "provisioners": [
    {
      "type": "powershell",
      "inline": [
          "Write-Host \"A literal dollar `$ must be escaped\"",
          "Write-Host \"A literal backtick `` must be escaped\"",
          "Write-Host \"Here `\"double quotes`\" must be escaped\"",
          "Write-Host \"Here `'single quotes`' don`'t really need to be\"",
          "Write-Host \"escaped... but it doesn`'t hurt to do so.\"",
      ]
    },

The above snippet should result in the following output on the Packer console:

==> amazon-ebs: Provisioning with Powershell...
==> amazon-ebs: Provisioning with powershell script: /var/folders/15/d0f7gdg13rnd1cxp7tgmr55c0000gn/T/packer-powershell-provisioner508190439
    amazon-ebs: A literal dollar $ must be escaped
    amazon-ebs: A literal backtick ` must be escaped
    amazon-ebs: Here "double quotes" must be escaped
    amazon-ebs: Here 'single quotes' don't really need to be
    amazon-ebs: escaped... but it doesn't hurt to do so.

» When Not To Escape...

Special characters appearing in user environment variable values and in the elevated_user and elevated_password fields will be automatically dealt with for the user. There is no need to use escapes in these instances.

{
  "variables": {
    "psvar": "My$tring"
  },
  ...
  "provisioners": [
    {
      "type": "powershell",
      "elevated_user": "Administrator",
      "elevated_password": "Super$3cr3t!",
      "inline": "Write-Output \"The dollar in the elevated_password is interpreted correctly\""
    },
    {
      "type": "powershell",
      "environment_vars": [
        "VAR1=A$Dollar",
        "VAR2=A`Backtick",
        "VAR3=A'SingleQuote",
        "VAR4=A\"DoubleQuote",
        "VAR5={{user `psvar`}}"
      ],
      "inline": [
        "Write-Output \"In the following examples the special character is interpreted correctly:\"",
        "Write-Output \"The dollar in VAR1:                            $Env:VAR1\"",
        "Write-Output \"The backtick in VAR2:                          $Env:VAR2\"",
        "Write-Output \"The single quote in VAR3:                      $Env:VAR3\"",
        "Write-Output \"The double quote in VAR4:                      $Env:VAR4\"",
        "Write-Output \"The dollar in VAR5 (expanded from a user var): $Env:VAR5\""
      ]
    }
  ]
  ...
}

The above snippet should result in the following output on the Packer console:

==> amazon-ebs: Provisioning with Powershell...
==> amazon-ebs: Provisioning with powershell script: /var/folders/15/d0f7gdg13rnd1cxp7tgmr55c0000gn/T/packer-powershell-provisioner961728919
    amazon-ebs: The dollar in the elevated_password is interpreted correctly
==> amazon-ebs: Provisioning with Powershell...
==> amazon-ebs: Provisioning with powershell script: /var/folders/15/d0f7gdg13rnd1cxp7tgmr55c0000gn/T/packer-powershell-provisioner142826554
    amazon-ebs: In the following examples the special character is interpreted correctly:
    amazon-ebs: The dollar in VAR1:                            A$Dollar
    amazon-ebs: The backtick in VAR2:                          A`Backtick
    amazon-ebs: The single quote in VAR3:                      A'SingleQuote
    amazon-ebs: The double quote in VAR4:                      A"DoubleQuote
    amazon-ebs: The dollar in VAR5 (expanded from a user var): My$tring