Terraform/OpenTofu Provider: Core Functions

Overview

Utilities that should have been Terraform/OpenTofu core functions.

While some of these can be implemented in HCL, some of them begin to push up against the limits of Terraform and the HCL2 configuration language. We also perform testing using the Terratest framework on a regular basis. Exposing these functions as both a Go library as well as a Terraform/OpenTofu provider enables us to use the same functionality in both our Terraform/OpenTofu applies as well as while using a testing framework.

Note

While it’s common knowledge that Terraform is great at standing up and managing Cloud infrastructure, it’s also good at running anything with an API. People regularly manage code repositories, DNS records, feature flags, identity and access management, content delivery, passwords, monitoring, alerts, zero trust network access, cryptographic signatures, and can even order a pizza.

This provider is more analogous to HashiCorp’s utility providers such as local, external, and archive.

Since earlier versions of Terraform/OpenTofu didn't have the concept of user-defined functions, the next step to open up the possibilities was to write a custom Provider which has the functions built-in, using existing support for inputs and outputs.

This does not add new syntax or constructs. Instead it uses the existing concepts around Providers, Resources, Data Sources, Variables, Outputs, and Functions to expose new custom-built functionality.

The goal of this provider is not to call any APIs, but to provide pre-built functions in the form of Data Sources or Provider Functions.

Compatibility testing

• We have automated testing that runs on every commit and every pull request.
• We intend for the Go libraries to work with all non-EOL versions of Go (i.e., current, current-1).
• Built using the Terraform Plugin Framework, which speaks Terraform Protocol v6.

Testing type	Details	Description
integration	Terraform 1.0–1.9	Executes the provider with this release, pulling from registry.terraform.io.
integration	OpenTofu 1.6–1.8	Executes the provider with this release, pulling from registry.opentofu.org.
unit	Go 1.22–1.23	Tests using these versions.
mutation	Go 1.22–1.23	Tests using these versions.
fuzz	Go 1.22–1.23	Tests using these versions.
terratest	Go 1.22–1.23	Tests using these versions.

Usage Examples

See the docs/ directory for user-facing documentation.

Documentation

Registries

• registry.terraform.io
• search.opentofu.org
• library.tf

Go Package

If you are using this as a Go library, see the documentation at pkg.go.dev.

More Information

After the provider is installed, you can run terraform-provider-corefunc on the CLI.

• Install with either terraform init or make build.
• The Go binary path (discovered by running ./find-go-bin.sh) is on your $PATH.

This will display the following text:

terraform-provider-corefunc

This binary is a plugin. These are not meant to be executed directly.
Please execute the program that consumes these plugins, which will
load any plugins automatically

However, by passing the --help flag, you can see the other options available, including a description of the software.

terraform-provider-corefunc --help

The provider has one primary sub-command: version. It includes long-form version information, including the build commit hash, build date, Go version, and external dependencies.

terraform-provider-corefunc version