Iterators and Dynamic Blocks

Handle loops and dynamic configurations using Terraform iterators.

tfts provides a type-safe way to work with Terraform’s for_each and dynamic blocks using the TerraformIterator class.

TerraformIterator

A TerraformIterator represents a collection that Terraform will iterate over at runtime. You can create an iterator from a list or a map.

import { TerraformIterator } from "tfts";

const listIterator = TerraformIterator.fromList(["a", "b", "c"]);
const mapIterator = TerraformIterator.fromMap({ key1: "val1", key2: "val2" });

Properties and Methods

Iterators provide access to the current element’s key and value:

• iterator.key: The key (for maps) or index (for lists).
• iterator.value: The value of the current element.

To access specific types from the value, use the getter methods:

• iterator.getString(path)
• iterator.getNumber(path)
• iterator.getBoolean(path)
• iterator.getList(path)

You can also retrieve all keys or values using iterator.keys() and iterator.values().

Resource for_each

To use an iterator with a resource, pass it to the forEach property.

const subnets = TerraformIterator.fromList(["10.0.1.0/24", "10.0.2.0/24"]);

new Subnet(stack, "subnet", {
  vpcId: vpc.id,
  cidrBlock: subnets.value,
  forEach: subnets,
});

Dynamic Blocks

Dynamic blocks allow you to generate multiple nested blocks based on a collection. Use the iterator.dynamic() method to define the block structure.

const ingressRules = TerraformIterator.fromList([
  { port: 80, protocol: "tcp" },
  { port: 443, protocol: "tcp" },
]);

new SecurityGroup(stack, "sg", {
  name: "web-sg",
  ingress: ingressRules.dynamic({
    fromPort: ingressRules.getNumber("port"),
    toPort: ingressRules.getNumber("port"),
    protocol: ingressRules.getString("protocol"),
    cidrBlocks: ["0.0.0.0/0"],
  }),
});

TerraformCount

For simple numeric loops, use TerraformCount.

import { TerraformCount } from "tfts";

const count = TerraformCount.of(3);

new Instance(stack, "server", {
  ami: "ami-123456",
  instanceType: "t2.micro",
  count: count,
  tags: {
    Name: `Server-${count.index}`,
  },
});

The count.index property provides the current iteration index (0, 1, 2, …).