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ADR-0001: Use OpenTofu, not Terraform

  • Status: Accepted
  • Date: 2026-05-24

Context

HashiCorp re-licensed Terraform from the Mozilla Public License (MPL 2.0) to the Business Source License (BSL) in August 2023. The BSL restricts production use in software that competes with HashiCorp's commercial offerings and is not OSI-approved. The Linux Foundation forked the last MPL-licensed Terraform release into OpenTofu, which continues under MPL 2.0.

For infra we need a permissively-licensed infrastructure tool that:

  • Supports HCL and the existing provider ecosystem we depend on (notably dmacvicar/libvirt).
  • Has a stable release cadence and a credible long-term governance model.
  • Carries no future license risk for commercial or internal-platform use.

OpenTofu satisfies all three: HCL-compatible, MPL-licensed, governed under the Linux Foundation, shipping regular releases (1.12.0 at the time of this ADR).

Decision

Use OpenTofu exclusively. Every command in documentation, scripts, CI, and day-to-day operations is tofu …. The Terraform CLI is not a supported entry point.

Shared ecosystem conventions — HCL, the .tf extension, the terraform { } block, terraform.tfvars, .terraform/, .terraform.lock.hcl — are language artifacts, not Terraform endorsements. OpenTofu reads and writes them natively.

Consequences

Positive

  • No license risk from HashiCorp's BSL.
  • OpenTofu-specific features become available as we bump the version pin: state encryption (1.7), native S3 locking (1.10), ephemeral resources (1.11).
  • Single, unambiguous command surface (tofu) in scripts and runbooks.

Negative

  • Contributors arriving from Terraform-only backgrounds install the tofu binary and adjust muscle memory.
  • Some providers publish only to the HashiCorp registry; OpenTofu's default registry mirrors most of them but we may need registry overrides for niche providers.

Pinning

  • required_version = ">= 1.6" in every versions.tf. 1.6 is the first GA OpenTofu release. ADR-0003 may push this to >= 1.10 once production adopts native S3 locking.

References