Only and Except

only and except are keywords used to filter what runs in your Packer build, they can be seen as a command line argument:

• -except=foo,bar,baz - Run all the builds and post-processors except those with the given comma-separated names. In legacy JSON templates, build names default to the types of their builders (e.g. docker or amazon-ebs or virtualbox-iso), unless a specific name attribute is specified within the configuration. In HCL2 templates, the "name" is the source block's "name" label, unless an in-build source definition adds the "name" configuration option. Any post-processor following a skipped post-processor will not run. Because post-processors can be nested in arrays a different post-processor chain can still run. A post-processor with an empty name will be ignored.

• -only=foo,bar,baz - Only run the builds with the given comma-separated names. In legacy JSON templates, build names default to the types of their builders (e.g. docker or amazon-ebs or virtualbox-iso), unless a specific name attribute is specified within the configuration. In HCL2 templates, the "name" is the source block's "name" label, unless an in-build source definition adds the "name" configuration option.

They can also be seen in a template to run or skip provisioners and/or post-processors for a specific source:

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

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

source "amazon-ebs" "third-example" {
}

build {
  name = "my_build"
  sources = [
    "source.amazon-ebs.first-example",
  ]
  source "source.amazon-ebs.second-example" {
    // setting the name field allows you to rename the source only for this
    // build section. To match this builder, you need to use
    // second-example-local-name, not second-example
    name = "second-example-local-name"
  }

  provisioner "shell-local" {
    only   = ["amazon-ebs.first-example"]
    inline = ["echo I will only run for the first example source"]
  }

  provisioner "shell-local" {
    except = ["amazon-ebs.second-example-local-name"]
    inline = ["echo I will never run for the second example source"]
  }
}

build {
  sources = [
    "source.amazon-ebs.third-example",
  ]
}

# this file will result in Packer creating three builds named:
#  my_build.amazon-ebs.first-example
#  my_build.amazon-ebs.second-example
#  amazon-ebs.third-example

Note that cli arguments can be used with a glob operator, using the previous configuration:

• packer build -only 'my_build.*' dir: will only run the builds in blocks named my_build.

• packer build -only '*.amazon-ebs.*' dir: will only run the builds with a source of type amazon-ebs.

• packer build -only '*.second-example-local-name' dir: will only run that specifically named build.