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tfts provides first-class support for Terraform variables, outputs, and locals, allowing you to create flexible and reusable infrastructure definitions.

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TerraformVariable

TerraformVariable allows you to define inputs for your stack. These can be provided via CLI arguments, environment variables, or terraform.tfvars files.

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Configuration

A variable can have several properties:
  • type: The data type (string, number, bool, list, map, etc.).
  • default: A default value if none is provided.
  • description: Documentation for the variable.
  • sensitive: If true, the value is masked in CLI output.
  • nullable: Whether the variable can be null.
  • validation: Custom validation rules.

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Usage

To use a variable’s value, you access its typed properties: value, stringValue, numberValue, booleanValue, or listValue. 
import { TerraformVariable, TerraformStack } from "tfts";
import { ComputeInstance } from "./.gen/providers/google/compute-instance";

const region = new TerraformVariable(stack, "region", {
  type: "string",
  default: "us-central1",
  description: "The GCP region to deploy to",
});

const instanceCount = new TerraformVariable(stack, "instance_count", {
  type: "number",
  default: 1,
});

new ComputeInstance(stack, "server", {
  // ...
  zone: `${region.stringValue}-a`,
});

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TerraformOutput

TerraformOutput is used to export information from your stack. This is useful for sharing data between stacks or displaying important information (like an IP address) after deployment. 
import { TerraformOutput } from "tfts";
import { ComputeInstance } from "./.gen/providers/google/compute-instance";

const instance = new ComputeInstance(stack, "web", { /* ... */ });

new TerraformOutput(stack, "instance_ip", {
  value: instance.networkInterface[0].accessConfig[0].natIp,
  description: "The public IP of the web server",
  sensitive: false,
});

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TerraformLocal

TerraformLocal (or “Locals”) allows you to assign a name to an expression. This is useful for avoiding repetition and simplifying complex logic. 
import { TerraformLocal } from "tfts";

const commonLabels = new TerraformLocal(stack, "common_labels", {
  environment: "production",
  team: "platform",
});

// Accessing locals
new SomeResource(stack, "res", {
  labels: commonLabels.expression,
});
Like variables, locals provide helper properties to cast the expression to specific types: asString, asNumber, asBoolean, and asList. 
const namePrefix = new TerraformLocal(stack, "prefix", "prod-app");

new SomeResource(stack, "bucket", {
  name: `${namePrefix.asString}-storage`,
});

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Complete Example

Here is how these concepts look when combined: 
import { App, TerraformStack, TerraformVariable, TerraformOutput, TerraformLocal } from "tfts";
import { StorageBucket } from "./.gen/providers/google/storage-bucket";

const app = new App();
const stack = new TerraformStack(app, "example");

// Variable
const env = new TerraformVariable(stack, "env", {
  type: "string",
  default: "dev",
});

// Local
const bucketName = new TerraformLocal(stack, "bucket_name", `my-app-${env.stringValue}-data`);

// Resource using Local
const bucket = new StorageBucket(stack, "data", {
  name: bucketName.asString,
  location: "US",
});

// Output
new TerraformOutput(stack, "bucket_url", {
  value: bucket.selfLink,
});

app.synth();