»The provisioner block

The provisioner block defines how a provisioner is configured.

# builds.pkr.hcl
build {
  # ...
  provisioner "shell" {
    inline = [
      "echo provisioning all the things",
      "echo the value of 'foo' is '${var.foo}'",
    ]
  }
}

Provisioners use builtin and third-party software to install and configure the machine image after booting. Provisioners prepare the system for use.

The list of available provisioners can be found in the provisioners section.

»Run on Specific Builds

You can use the only or except configurations to run a provisioner only with specific builds. These two configurations do what you expect: only will only run the provisioner on the specified builds and except will run the provisioner on anything other than the specified builds.

An example of only being used is shown below, but the usage of except is effectively the same:

# builds.pkr.hcl

source "amazon-ebs" "first-example" {
  #...
}

source "amazon-ebs" "second-example" {
  #...
}

build {
  source = [
    "source.amazon-ebs.first-example",
    "source.amazon-ebs.second-example",
  ]
  provisioner "shell" {
    # This provisioner only runs for the 'first-example' source.
    only = ["source.amazon-ebs.first-example"] 

    inline = [
      "echo provisioning all the things",
      "echo the value of 'foo' is '${var.foo}'",
    ]
  }
  provisioner "shell" {
    # This runs with all sources.
    inline = [
        "echo Hi World!"
      ]
  }
}

The values within only or except are build names, not builder types.

»Pausing Before Running

With certain provisioners it is sometimes desirable to pause for some period of time before running it. Specifically, in cases where a provisioner reboots the machine, you may want to wait for some period of time before starting the next provisioner.

Every provisioner definition in a Packer template can take a special configuration pause_before that is the amount of time to pause before running that provisioner. By default, there is no pause. An example is shown below:

# builds.pkr.hcl
build {
  # ...
  provisioner "shell" {
      inline = [
        "echo provisioning all the things",
        "echo the value of 'foo' is '${var.foo}'",
      ]
      pause_before = "10s"
  }
}

For the above provisioner, Packer will wait 10 seconds before uploading and executing the shell script.

»Retry on error

With certain provisioners it is sometimes desirable to retry when it fails. Specifically, in cases where the provisioner depends on external processes that are not done yet.

Every provisioner definition in a Packer template can take a special configuration max_retries that is the maximum number of times a provisioner will retry on error. By default, there max_retries is zero and there is no retry on error. An example is shown below:

# builds.pkr.hcl
build {
  # ...
  provisioner "shell" {
      inline = [
        "echo provisioning all the things",
        "echo the value of 'foo' is '${var.foo}'",
      ]
      max_retries = 5
  }
}

For the above provisioner, Packer will retry maximum five times until stops failing. If after five retries the provisioner still fails, then the complete build will fail.

»Timeout

Sometimes a command can take much more time than expected

Every provisioner definition in a Packer template can take a special configuration timeout that is the amount of time to wait before considering that the provisioner failed. By default, there is no timeout. An example is shown below:

# builds.pkr.hcl
build {
  # ...
  provisioner "shell" {
      inline = [
        "echo provisioning all the things",
        "echo the value of 'foo' is '${var.foo}'",
      ]
      timeout = "5m"
  }
}

For the above provisioner, Packer will cancel the script if it takes more than 5 minutes.

Timeout has no effect in debug mode.