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CDK Terrain v0.23.4 lets you declare, in cdktf.json, the Terraform and OpenTofu versions your project supports. Synth-time validations check features against that declaration (cdk-terrain#269).
Later releases added more validations against targetVersions: function availability became the default in v0.24, and v0.25 validates moved blocks, import blocks, terraform_data, and the cloud backend at synth time instead of probing the installed binary.

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What changed

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New targetVersions field

targetVersions takes an npm semver range per product, keyed by terraform and opentofu:
  • A feature passes validation only if every version in the declared range of every targeted product supports it. If you use a feature that needs a newer version, raise the floor of your declared range.
  • If you leave out a product, your project does not target it. If you leave out targetVersions entirely, CDKTN assumes both products, from terraform >=1.5.7 and opentofu >=1.6.0.
  • CDKTN validates the field when it parses cdktf.json. Terraform’s ~> constraint syntax is rejected, because npm semver would read it with different semantics.
  • cdktn init writes the default ranges explicitly into new projects.
In v0.23.4, two validations used the declared targets: function availability (behind the validateFunctionVersions flag) and S3-native state locking, which requires Terraform or OpenTofu 1.10 or later when useLockfile is set.

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Synthesis never runs a binary for these checks

Validations against targetVersions are declarative. Synthesis behaves the same in CI, in package builds, and on machines without Terraform or OpenTofu installed.

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Opt-in installed-binary check

Set "validateInstalledBinary": true to have cdktn diff, cdktn deploy, cdktn destroy, and cdktn output verify the installed binary before they run it. The command fails if CDKTN can’t tell whether the binary is Terraform or OpenTofu, if that product isn’t declared in targetVersions, or if its version is outside the declared range. The default is false.

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Learn more

See Declare Target Runtimes for the full reference.