Using previous versions of Terraform no longer works

[neefrehman]

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Overview of the Issue

Updating Atlantis has just broken our usage of Terraform due to non-supported versions, making us need to manually upgrade to the latest "default" version (1.8.3).

Usually our updates of Atlantis work fine if we update our terraform version slightly later, due to the multiple supported versions stated in the docs (via Terraform config, in our case). But, after our update to 0.28.0 we noticed that subsequent calls to atlantis were failing due to version support problems.

After some searching, I noticed that the logic around AVAILABLE_TERRAFORM_VERSIONS was removed in #4341, and so potentially that change is related to this issue.

As a separate note, one issue that made version selection slightly more confusing in our case, is that the supported/default Terraform version was not clearly signposted in the release notes. I initially migrated to 1.7.2 after seeing #4203, while skipping past #4419 due to the commit being considered a (chore) change. It would be helpful to standardise the label for version bumps, or signpost them in other ways.

Reproduction Steps

Try to use Atlantis with Terraform's configuration set to 1.7.2

Logs

Environment details

• Atlantis version: 0.28.0
• Deployment method: helm

Atlantis server-side config file:

      repos:
        - id: "/.*/"
          workflow: terragrunt
          allowed_overrides: [workflow, apply_requirements, plan_requirements]
          apply_requirements: [approved, mergeable]
          pre_workflow_hooks:
            - run: terragrunt-atlantis-config generate --output atlantis.yaml --autoplan --automerge --create-workspace --parallel --filter terraform
      workflows:
        terragrunt:
          plan:
            steps:
            - env:
                name: TERRAGRUNT_TFPATH
                command: 'echo "terraform${ATLANTIS_TERRAFORM_VERSION}"'
            - run: terragrunt plan --terragrunt-log-level error -no-color -out=$PLANFILE
            - run: terragrunt show -json $PLANFILE > $SHOWFILE
          apply:
            steps:
            - env:
                name: TERRAGRUNT_TFPATH
                command: 'echo "terraform${ATLANTIS_TERRAFORM_VERSION}"'
            - run: terragrunt apply -no-color $PLANFILE