Build AWS infrastructure with CDK for Terraform

The Cloud Development Kit for Terraform (CDKTF) allows you to define your infrastructure in a familiar programming language such as TypeScript, Python, Go, C#, or Java. CDKTF generates Terraform configuration in JSON, then automatically applies that configuration via Terraform to provision your infrastructure.

In this tutorial, you will provision an EC2 instance on AWS using your preferred programming language.

If you do not have CDKTF installed on your system, follow the steps in the install CDKTF tutorial to install it before you continue with this tutorial.

Prerequisites

To follow this tutorial, you need the following installed locally:

• Terraform v1.2+
• An HCP Terraform account, with CLI authentication configured
• CDK for Terraform v0.15+
• an AWS account
• AWS Credentials configured for use with Terraform

Terraform and CDKTF will use credentials set in your environment or through other means as described in the Terraform documentation.

You will also need to install a recent version of the programming language you will use for this tutorial. We have verified this tutorial works with the following language versions.

C# .Net Core Runtime v3.1

For MacOS, you will also need XCode and the Command Line Tools for XCode.

Initialize a new CDK for Terraform application

Start by creating a directory named learn-cdktf for your project.

$ mkdir learn-cdktf

Then navigate into it.

$ cd learn-cdktf

Inside the directory, run cdktf init, specifying the template for your preferred language and Terraform's AWS provider. Select your HCP Terraform Organization when prompted, and use the default name learn-cdktf for your HCP Terraform Workspace. CDKTF will also prompt you for other information about your project, such as the name and description. Accept the defaults for these options.

$ cdktf init --template="csharp" --providers="aws@~>4.0"
? Project Name learn-cdktf
? Project Description A simple getting started project for cdktf.

Detected Terraform Cloud token.

We will now set up Terraform Cloud for your project.

? Terraform Cloud Organization Name <YOUR_ORG>

We are going to create a new Terraform Cloud Workspace for your project.

? Terraform Cloud Workspace Name learn-cdktf

Setting up remote state backend and workspace in Terraform Cloud.

Generating Terraform Cloud configuration for '<YOUR_ORG>' organization and 'learn-cdktf' workspace.....
  Determining projects to restore...
  Restored /Users/YOU/code/learn-cdktf/MyTerraformStack.csproj (in 1.6 sec).
========================================================================================================

  Your cdktf csharp project is ready!

  cat help                Prints this message

  Compile:
    dotnet build          Builds your dotnet packages

  Synthesize:
    cdktf synth [stack]   Synthesize Terraform resources to cdktf.out/

  Diff:
    cdktf diff [stack]    Perform a diff (terraform plan) for the given stack

  Deploy:
    cdktf deploy [stack]  Deploy the given stack

  Destroy:
    cdktf destroy [stack] Destroy the given stack

  Learn more about using modules and providers https://cdk.tf/modules-and-providers

Use Providers:

  Use the add command to add both prebuilt providers (if available) or locally generated providers:

  cdktf provider add "aws@~>3.0" null kreuzwerker/docker

  You can find all prebuilt providers on nuget: https://www.nuget.org/packages?q=HashiCorp.Cdktf.Providers
  You can also install these providers directly through dotnet:

  dotnet add package HashiCorp.Cdktf.Providers.Aws
  dotnet add package HashiCorp.Cdktf.Providers.Google
  dotnet add package HashiCorp.Cdktf.Providers.Azurerm
  dotnet add package HashiCorp.Cdktf.Providers.Docker
  dotnet add package HashiCorp.Cdktf.Providers.Github
  dotnet add package HashiCorp.Cdktf.Providers.Null

  You can also build any module or provider locally. Learn more: https://cdk.tf/modules-and-providers

========================================================================================================

Checking whether pre-built provider exists for the following constraints:
  provider: aws
  version : ~>4.0
  language: c#
  cdktf   : 0.15.0

Found pre-built provider.
Package installed.

CDKTF provides packages with prebuilt classes for each supported programming language for many common Terraform providers that you can use in your CDKTF projects. The cdktf init command you just ran will find a pre-built AWS provider that you will use for this project. For other Terraform providers and modules, CDKTF automatically generates the appropriate classes for your chosen language.

Define your CDK for Terraform Application

Open the MainStack.cs file to view your application code. The template creates a scaffold with no functionality.

Replace the contents of MainStack.cs with the following code for a new C# application, which uses the CDK to provision an AWS EC2 instance in us-west-1.

using System;
using Constructs;
using HashiCorp.Cdktf;

using HashiCorp.Cdktf.Providers.Aws.Provider;
using HashiCorp.Cdktf.Providers.Aws.Instance;

namespace MyCompany.MyApp
{
    class MainStack : TerraformStack
    {
        public MainStack(Construct scope, string id) : base(scope, id)
        {
            new AwsProvider(this, "AWS", new AwsProviderConfig { Region = "us-west-1" });

            Instance instance = new Instance(this, "compute", new InstanceConfig
            { 
                Ami = "ami-01456a894f71116f2",
                InstanceType = "t2.micro",
            });

            new TerraformOutput(this, "public_ip", new TerraformOutputConfig
            {
                Value = instance.PublicIp
            });
        }
    }
}

Open the Program.cs file to view your application's Main() function.

Replace the contents of Program.cs with the following code for a new C# application, which uses your stack to provision an AWS EC2 instance, and stores its state in HCP Terraform.

using System;
using Constructs;
using HashiCorp.Cdktf;

namespace MyCompany.MyApp
{
    class Program
    {
        public static void Main(string[] args)
        {
            App app = new App();
            MainStack stack = new MainStack(app, "aws_instance");
            new RemoteBackend(
                stack,
                new RemoteBackendProps
                {
                    Hostname = "app.terraform.io",
                    Organization = "<YOUR_ORG>",
                    Workspaces = new NamedRemoteWorkspace("learn-cdktf")
                }
            );

            app.Synth();
        }
    }
}

Replace <YOUR_ORG> with the HCP Terraform organization name you chose when you ran terraform init earier. If you chose a different workspace name, replace learn-cdktf with that name.

Examine the code

Most of the code is similar to concepts found in a traditional Terraform configuration written in HCL, but there are a few notable differences. Review the code for the programming language you have selected.

You must explicitly import any classes your C# code uses. For example, you will use TerraformOutput from the HashiCorp.Cdktf package to create a Terraform output value for your EC2 instance's public IP address.

using System;
using Constructs;
using HashiCorp.Cdktf;

The example code also imports the AWS provider and other resources from the package you installed earlier. In this case you need the Aws and Ec2 classes for your compute resource.

using HashiCorp.Cdktf.Providers.Aws.Provider;
using HashiCorp.Cdktf.Providers.Aws.Instance;

The MyStack class defines a new stack in the MyCompany.MyApp namespace, which contains code to define your provider and all of your resources.

namespace MyCompany.MyApp
{
    class MyStack : TerraformStack
    {
        public MyStack(Construct scope, string id) : base(scope, id)
        {

The code configures the AWS provider to use the us-west-1 region.

            new AwsProvider(this, "AWS", new AwsProviderConfig { Region = "us-west-1" });

The code configures the configure AwsProvider by passing in an AwsProviderConfig object with keys and values that map to Terraform arguments as listed in the AWS provider documentation.

The Instance class creates a t2.micro EC2 instance with an AWS ami.

            Instance instance = new Instance(this, "compute", new InstanceConfig
            { 
                Ami = "ami-01456a894f71116f2",
                InstanceType = "t2.micro",
            });

The code configures the instance with an InstanceConfig object, using camel case for Terraform arguments that correspond to the AWS provider documentation.

The code stores the instance as a variable so that the TerraformOutput below can reference the instance's PublicIp attribute.

            new TerraformOutput(this, "public_ip", new TerraformOutputConfig
            {
                Value = instance.PublicIp
            });

When you write CDKTF code with an IDE, use it view the properties and functions of the classes, variables, and packages in your code. This example uses the PublicIp method from the instance variable.

Finally, in Program.cs your application uses the stack you have defined, configures a remote backend to store your project's state in HCP Terraform, and calls app.Synth() to generate Terraform configuration.

        public static void Main(string[] args)
        {
            App app = new App();
            MyStack stack = new MyStack(app, "aws_instance");
            new RemoteBackend(stack, new RemoteBackendProps
            {
                Hostname = "app.terraform.io",
                Organization = "<YOUR_ORG>",
                Workspaces = new NamedRemoteWorkspace("learn-cdktf")
            });

            app.Synth();
        }

Provision infrastructure

Now that you have initialized the project with the AWS provider and written code to provision an instance, it's time to deploy it by running cdktf deploy. When CDKTF asks you to confirm the deploy, respond with a yes.

$ cdktf deploy
Deploying Stack: aws_instance
Resources
 ✔ AWS_INSTANCE         compute             aws_instance.compute

Summary: 1 created, 0 updated, 0 destroyed.

Output: public_ip = 50.18.17.102

The cdktf deploy command runs terraform apply in the background.

After the instance is created, visit the AWS EC2 Dashboard.

Notice that the CDK deploy command printed out the public_ip output value, which matches the instance's public IPv4 address.

Change infrastructure by adding the Name tag

Add a tag to the EC2 instance.

Add the System.Collections.Generic namespace to the top of MainStack.cs.

using System;
using Constructs;
using HashiCorp.Cdktf;
using System.Collections.Generic;

Next, update the Instance in MainStack.cs to add a Name tag.

            Instance instance = new Instance(this, "compute", new InstanceConfig
            {
                Ami = "ami-01456a894f71116f2",
                InstanceType = "t2.micro",
                Tags = new Dictionary<string, string>
                {
                    { "Key", "Name" },
                    { "Value", "CDKTF-Demo" }
                }
            });

Deploy your updated application. Confirm your deploy by choosing Approve.

$ cdktf deploy
aws_instance  Initializing the backend...
aws_instance
              Successfully configured the backend "remote"! Terraform will automatically
              use this backend unless the backend configuration changes.
aws_instance  Initializing provider plugins...
aws_instance  - Finding hashicorp/aws versions matching "4.23.0"...
aws_instance  - Using hashicorp/aws v4.23.0 from the shared cache directory
##...
              Plan: 1 to add, 0 to change, 0 to destroy.

              Changes to Outputs:
              + public_ip = (known after apply)
aws_instance
              ─────────────────────────────────────────────────────────────────────────────

              Saved the plan to: plan

              To perform exactly these actions, run the following command to apply:
              terraform apply "plan"

Please review the diff output above for aws_instance
❯ Approve  Applies the changes outlined in the plan.
  Dismiss
  Stop
##...
              Apply complete! Resources: 1 added, 0 changed, 0 destroyed.

              Outputs:


aws_instance  public_ip = "54.219.167.18"

  aws_instance
  public_ip = 54.219.167.18

Clean up your infrastructure

Destroy the application by running cdktf destroy. Confirm your destroy by choosing Approve.

$ cdktf destroy
aws_instance  Initializing the backend...
aws_instance  Initializing provider plugins...
              - Reusing previous version of hashicorp/aws from the dependency lock file
aws_instance  - Using previously-installed hashicorp/aws v4.23.0
##...
              Plan: 0 to add, 0 to change, 1 to destroy.

              Changes to Outputs:
              - public_ip = "54.219.167.18" -> null
aws_instance
              ─────────────────────────────────────────────────────────────────────────────

              Saved the plan to: plan

              To perform exactly these actions, run the following command to apply:
              terraform apply "plan"

Please review the diff output above for aws_instance
❯ Approve  Applies the changes outlined in the plan.
  Dismiss
  Stop
##...
              Plan: 0 to add, 0 to change, 1 to destroy.

              Changes to Outputs:
              - public_ip = "54.219.167.18" -> null
aws_instance  aws_instance.compute (compute): Destroying... [id=i-0fc8d2e3931b28db3]
aws_instance  aws_instance.compute (compute): Still destroying... [id=i-0fc8d2e3931b28db3, 10s elapsed]
aws_instance  aws_instance.compute (compute): Still destroying... [id=i-0fc8d2e3931b28db3, 20s elapsed]
aws_instance  aws_instance.compute (compute): Still destroying... [id=i-0fc8d2e3931b28db3, 30s elapsed]
aws_instance  aws_instance.compute (compute): Destruction complete after 30s
aws_instance
              Destroy complete! Resources: 1 destroyed.

Destroying your CDKTF application will not remove the HCP Terraform workspace that stores your project's state. Log into the HCP Terraform application and delete the workspace.

Next steps

Now you have deployed, modified, and deleted an AWS EC2 instance using CDKTF!

CDKTF is capable of much more. For example, you can:

• Use the cdktf synth command to generate JSON which can be used by the Terraform executable to provision infrastructure using terraform apply and other Terraform commands.
• Use Terraform providers and modules.
• Use programming language features (like class inheritance) or data from other sources to augment your Terraform configuration.
• Use CDKTF with HCP Terraform for persistent storage of your state file and for team collaboration.

For other examples, refer to the CDKTF documentation repository. In particular, check out the:

• CDKTF Architecture documentation for an overview of CDKTF's architecture.
• Community documentation to learn how to engage with the CDKTF developer community.
• Review example code in several programming languages.