How does tfenv help manage multiple Terraform versions, and why is version pinning important?

Think of a chef who needs different ovens for different recipes — one recipe requires a convection oven at 350F, another requires a gas oven at 400F. tfenv lets you switch ovens (Terraform versions) per recipe (project) without uninstalling and reinstalling each time.

tfenv works like nvm for Node.js or pyenv for Python. You install it once, then use tfenv install to download specific Terraform versions. tfenv use 1.7.5 switches your active version. Most importantly, you can place a .terraform-version file in your project root containing just the version number (e.g., 1.7.5), and tfenv automatically switches to that version when you enter the directory.

Version pinning matters because Terraform versions are not always backward-compatible. A state file written by Terraform 1.8 cannot be read by Terraform 1.7. Provider behavior can change between versions — for example, the AWS provider might change default values for security group rules. If one team member runs Terraform 1.8 and another runs 1.7, they can corrupt the state file or produce different plan outputs from the same code.

At production scale, teams enforce version pinning at multiple levels: .terraform-version in the repo root for tfenv users, required_version constraint in the Terraform block (e.g., required_version = "~> 1.7.0"), and a pinned Terraform version in the CI/CD pipeline Docker image. This triple-lock ensures everyone — developers, CI, and production — uses the exact same Terraform version.

The non-obvious gotcha is that tfenv install latest installs the newest version, which might be a major release with breaking changes. Always use explicit version numbers in .terraform-version files, never latest. Also, some teams forget to update the required_version constraint when they upgrade, causing confusion when tfenv installs a newer version that the constraint blocks.