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Constructs are the basic building blocks of tfts applications. By extending the Construct class, you can group multiple resources together into a single, reusable component. This allows you to encapsulate complex infrastructure patterns and share them across projects.

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Extending the Construct Class

To create a custom construct, define a class that extends Construct. 
import { Construct } from "tfts";
import { Vpc } from "./.gen/providers/aws/vpc";
import { Subnet } from "./.gen/providers/aws/subnet";

export interface MyVpcProps {
  cidrBlock: string;
  publicSubnetCidr: string;
}

export class MyVpc extends Construct {
  public readonly vpcId: string;
  public readonly publicSubnetId: string;

  constructor(scope: Construct, id: string, props: MyVpcProps) {
    super(scope, id);

    const vpc = new Vpc(this, "vpc", {
      cidrBlock: props.cidrBlock,
      enableDnsHostnames: true,
    });

    const subnet = new Subnet(this, "public-subnet", {
      vpcId: vpc.id,
      cidrBlock: props.publicSubnetCidr,
    });

    this.vpcId = vpc.id;
    this.publicSubnetId = subnet.id;
  }
}

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Parameterized Infrastructure

By passing a props object to the constructor, you can make your construct configurable. This allows you to reuse the same logic for different environments or use cases. 
// Usage
const network = new MyVpc(stack, "network", {
  cidrBlock: "10.0.0.0/16",
  publicSubnetCidr: "10.0.1.0/24",
});

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Composition Patterns

Constructs can be composed of other constructs, allowing you to build deep hierarchies of infrastructure. 
export class WebApplication extends Construct {
  constructor(scope: Construct, id: string, props: WebAppProps) {
    super(scope, id);

    const network = new MyVpc(this, "network", {
      cidrBlock: "10.1.0.0/16",
      publicSubnetCidr: "10.1.1.0/24",
    });

    new ComputeInstance(this, "server", {
      vpcId: network.vpcId,
      subnetId: network.publicSubnetId,
      // ... other props
    });
  }
}

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Best Practices

  • Encapsulation: Keep internal resources private or protected unless they need to be accessed from outside the construct.
  • Naming: Use descriptive IDs for child resources. tfts will automatically prefix these IDs with the construct’s ID to ensure uniqueness in the Terraform configuration.
  • Validation: You can add validation logic inside the constructor to ensure that the provided properties are valid before synthesis.
  • Defaults: Provide sensible default values for optional properties to make your construct easier to use.