terraform/tools/terraform-bundle

terraform-bundle

terraform-bundle is a helper program to create "bundle archives", which are zip files that contain both a particular version of Terraform and a number of provider plugins.

Normally terraform init will download and install the plugins necessary to work with a particular configuration, but sometimes Terraform is deployed in a network that, for one reason or another, cannot access the official plugin repository for automatic download.

terraform-bundle provides an alternative, by allowing the auto-download process to be run out-of-band on a separate machine that does have access to the repository. The result is a zip file that can be extracted onto the target system to install both the desired Terraform version and a selection of providers, thus avoiding the need for on-the-fly plugin installation.

Building

To build terraform-bundle from source, set up a Terraform development environment per Terraform's own README and then install this tool from within it:

$ go install ./tools/terraform-bundle

This will install terraform-bundle in $GOPATH/bin, which is assumed by the rest of this README to be in PATH.

Usage

terraform-bundle uses a simple configuration file to define what should be included in a bundle. This is designed so that it can be checked into version control and used by an automated build and deploy process.

The configuration file format works as follows:

terraform {
  # Version of Terraform to include in the bundle. An exact version number
  # is required.
  version = "0.10.0"
}

# Define which provider plugins are to be included
providers {
  # Include the newest "aws" provider version in the 1.0 series.
  aws = ["~> 1.0"]

  # Include both the newest 1.0 and 2.0 versions of the "google" provider.
  # Each item in these lists allows a distinct version to be added. If the
  # two expressions match different versions then _both_ are included in
  # the bundle archive.
  google = ["~> 1.0", "~> 2.0"]
}

The terraform block defines which version of Terraform will be included in the bundle. An exact version is required here.

The providers block defines zero or more providers to include in the bundle along with core Terraform. Each attribute in this block is a provider name, and its value is a list of version constraints. For each given constraint, terraform-bundle will find the newest available version matching the constraint and include it in the bundle.

It is allowed to specify multiple constraints for the same provider, in which case multiple versions can be included in the resulting bundle. Each constraint string given results in a separate plugin in the bundle, unless two constraints resolve to the same concrete plugin.

Including multiple versions of the same provider allows several configurations running on the same system to share an installation of the bundle and to choose a version using version constraints within the main Terraform configuration. This avoids the need to upgrade all configurations to newer versions in lockstep.

After creating the configuration file, e.g. terraform-bundle.hcl, a bundle zip file can be produced as follows:

$ terraform-bundle package terraform-bundle.hcl

By default the bundle package will target the operating system and CPU architecture where the tool is being run. To override this, use the -os and -arch options. For example, to build a bundle for on-premises Terraform Enterprise:

$ terraform-bundle package -os=linux -arch=amd64 terraform-bundle.hcl

The bundle file is assigned a name that includes the core Terraform version number, a timestamp to the nearest hour of when the bundle was built, and the target OS and CPU architecture. It is recommended to refer to a bundle using this composite version number so that bundle archives can be easily distinguished from official release archives and from each other when multiple bundles contain the same core Terraform version.

Provider Resolution Behavior

Terraform's provider resolution behavior is such that if a given constraint can be resolved by any plugin already installed on the system it will use the newest matching plugin and not attempt automatic installation.

Therefore if automatic installation is not desired, it is important to ensure that version constraints within Terraform configurations do not exclude all of the versions available from the bundle. If a suitable version cannot be found in the bundle, Terraform will attempt to satisfy that dependency by automatic installation from the official repository.

To disable automatic installation altogether -- and thus cause a hard failure if no local plugins match -- the -plugin-dir option can be passed to terraform init, giving the directory into which the bundle was extracted. The presence of this option overrides all of the normal automatic discovery and installation behavior, and thus forces the use of only the plugins that can be found in the directory indicated.

The downloaded provider archives are verified using the same signature check that is used for auto-installed plugins, using Hashicorp's release key. At this time, the core Terraform archive itself is not verified in this way; that may change in a future version of this tool.

Installing a Bundle in On-premises Terraform Enterprise

If using a private install of Terraform Enterprise in an "air-gapped" environment, this tool can produce a custom tool package for Terraform, which includes a set of provider plugins along with core Terraform.

To create a suitable bundle, use the -os and -arch options as described above to produce a bundle targeting linux_amd64. You can then place this archive on an HTTP server reachable by the Terraform Enterprise hosts and install it as per Managing Tool Versions.

After choosing the "Add Tool Version" button, be sure to set the Tool to "terraform" and then enter as the Version the generated bundle version from the bundle filename, which will be of the form N.N.N-bundleYYYYMMDDHH. Enter the URL at which the generated bundle archive can be found, and the SHA256 hash of the file which can be determined by running the tool sha256sum with the given file.

The new bundle version can then be selected as the Terraform version for any workspace. When selected, configurations that require only plugins included in the bundle will run without trying to auto-install.

Note that the above does not apply to Terraform Pro, or to Terraform Premium when not running a private install. In these packages, Terraform versions are managed centrally across all organizations and so custom bundles are not supported.

For more information on the available Terraform Enterprise packages, see the Terraform product site.