Advanced Terraform and CDK Techniques for Experienced DevOps Engineers

If you are an experienced DevOps engineer, you must have heard of Terraform and AWS Cloud Development Kit (CDK). These two technologies are becoming increasingly popular for infrastructure deployment. Terraform is an infrastructure as code tool that allows you to provision and manage infrastructure resources on various cloud platforms. CDK, on the other hand, is a software development framework used to define cloud infrastructure in code and provision them to your AWS account.

In this article, we will delve deep into advanced Terraform and CDK techniques that experienced DevOps engineers must know. Some of the topics we will cover include:

• Creating and managing reusable Terraform modules
• Integrating Terraform with CDK
• Automatic infrastructure deployment with CDK pipelines
• Advanced Terraform features like workspaces and resource targeting

Creating and Managing Reusable Terraform Modules

As an experienced DevOps engineer, you must know how to create reusable Terraform modules. These modules make it easy for you to provision infrastructure resources and also allow for easy collaboration with other developers. In this section, we will discuss how to create and manage reusable Terraform modules.

Creating a Terraform Module

To create a Terraform module, you need to define variables that will be used to provision the infrastructure resource. Here is an example module that creates an EC2 instance:

# modules/ec2-instance/main.tf
variable "name" {}
variable "ami" {}
variable "instance_type" {}

resource "aws_instance" "${var.name}" {
  ami           = var.ami
  instance_type = var.instance_type

  tags = {
    Name = var.name
  }
}

In the above module, we define variables for the instance name, AMI, and instance type. We then use the aws_instance resource to create an EC2 instance with the specified parameters.

Using a Terraform Module

Using a Terraform module is as simple as referencing it in your code. Here is an example of how to use the above module:

# main.tf
module "web_server" {
  source = "./modules/ec2-instance"
  name   = "web-server"
  ami    = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"
}

In the above code, we reference the ec2-instance module and specify the required variables.

Publishing a Terraform Module

Once you have created a Terraform module, you can publish it to the Terraform registry to make it accessible to others. Here are the steps to follow:

1. Create a GitHub repository for the module.
2. Create a README.md file that describes the module.
3. Create a main.tf file that defines the module.
4. Initialize the repository with terraform init.
5. Tag the repository with a version number.
6. Publish the module to the registry with terraform registry publish.

Integrating Terraform with CDK

Now that we know how to create and manage reusable Terraform modules, let's see how to integrate Terraform with CDK. CDK allows you to define your infrastructure in code, and it generates CloudFormation templates based on the code. CloudFormation then uses these templates to provision the infrastructure on AWS.

To integrate Terraform with CDK, we need to use the CloudFormationStack construct. This construct allows us to provision our infrastructure using Terraform templates.

Creating a CDK App

To create a CDK app, we need to install the aws-cdk-lib package:

$ npm install aws-cdk-lib

We can then create a new CDK app using the following command:

$ cdk init app --language=typescript

This will create a new CDK app in TypeScript.

Creating a Terraform Stack

To create a Terraform stack, we need to use the TerraformStack construct. This construct allows us to define our Terraform template and other necessary resources:

// lib/my-stack.ts
import * as cdk from 'aws-cdk-lib';
import { Construct } from 'constructs';
import { TerraformStack } from 'cdk-terraform-bridge';
 
export class MyStack extends TerraformStack {
  constructor(scope: Construct, id: string) {
    super(scope, id, {
      terraformStackPath: `${__dirname}/terraform`,
    });
  }
}

In the above code, we define a CDK stack that extends the TerraformStack class. We then specify the path to our Terraform template.

Creating a CDK App with the Terraform Stack

Once we have created the MyStack class, we can add it to our CDK app:

// bin/my-app.ts
import * as cdk from 'aws-cdk-lib';
import { MyStack } from '../lib/my-stack';

const app = new cdk.App();
new MyStack(app, 'MyStack');

In the above code, we create a new CDK app and add our MyStack stack to it.

Running the CDK App

To run the CDK app, we need to execute the following command:

$ cdk deploy

This will provision our infrastructure resources using our Terraform template.

Automatic Infrastructure Deployment with CDK Pipelines

CDK Pipelines allow us to automatically deploy infrastructure changes to our AWS account. It integrates with CodePipeline and CodeBuild to create a continuous delivery pipeline for our infrastructure.

To use CDK Pipelines, we need to define a pipeline stack that creates a CodePipeline and adds stages to it. Here is an example pipeline stack:

// lib/pipeline-stack.ts
import * as cdk from 'aws-cdk-lib';
import * as codepipeline from 'aws-cdk-lib/aws-codepipeline';
import * as cpactions from 'aws-cdk-lib/aws-codepipeline-actions';
import * as codebuild from 'aws-cdk-lib/aws-codebuild';
import { SecretValue } from 'aws-cdk-lib';
import { Construct } from 'constructs';

interface PipelineStackProps extends cdk.StackProps {
  readonly githubOwner: string;
  readonly repo: string;
  readonly branch: string;
  readonly tfStackName: string;
}
 
export class PipelineStack extends cdk.Stack {
  constructor(scope: Construct, id: string, props: PipelineStackProps) {
    super(scope, id, props);

    const sourceOutput = new codepipeline.Artifact();
    const sourceAction = new cpactions.GitHubSourceAction({
      actionName: 'GitHub',
      owner: props.githubOwner,
      repo: props.repo,
      branch: props.branch,
      oauthToken: SecretValue.secretsManager('github-token'),
      output: sourceOutput,
    });

    const project = new codebuild.PipelineProject(this, 'MyProject', {
      environment: {
        buildImage: codebuild.LinuxBuildImage.UBUNTU_14_04_NODEJS_10_14_1,
      },
    });

    const buildOutput = new codepipeline.Artifact();
    const buildAction = new cpactions.CodeBuildAction({
      actionName: 'CodeBuild',
      input: sourceOutput,
      outputs: [ buildOutput ],
      project: project,
    });

    const cloudFormationAction = new cpactions.CloudFormationCreateUpdateStackAction({
      actionName: 'CloudFormation',
      stackName: props.tfStackName,
      templatePath: buildOutput.atPath('terraform.yml'),
      adminPermissions: true,
    });

    const pipeline = new codepipeline.Pipeline(this, 'MyPipeline');
    pipeline.addStage({
      stageName: 'Source',
      actions: [ sourceAction ],
    });

    pipeline.addStage({
      stageName: 'Build',
      actions: [ buildAction ],
    });

    pipeline.addStage({
      stageName: 'Deploy',
      actions: [ cloudFormationAction ],
    });
  }
}

In the above code, we define a PipelineStack that creates a CodePipeline and adds stages to it. The GitHubSourceAction retrieves the code changes from our GitHub repository, and the CodeBuildAction build our project and produces a terraform.yml template that is used by the CloudFormationCreateUpdateStackAction to create or update the specified CloudFormation stack.

Advanced Terraform Features

In this section, we will discuss some advanced Terraform features that experienced DevOps engineers must know.

Workspaces

Workspaces allow us to manage multiple deployments of our infrastructure resources. They allow us to use the same codebase to manage resources in different environments. Here is an example of how to use workspaces:

$ terraform workspace new dev
$ terraform apply

In the above example, we create a new workspace for our development environment and apply the Terraform code. We can then create another workspace for our production environment and apply the code without affecting the development environment.

Resource Targeting

Resource targeting allows us to target specific resources when applying Terraform code. This is useful when we need to update or remove a specific resource without affecting others. Here is an example of how to target a specific resource:

$ terraform apply -target=aws_instance.web_server

In the above example, we apply the Terraform code and target the aws_instance resource with the name web_server.

Conclusion

In this article, we have covered advanced Terraform and CDK techniques that experienced DevOps engineers must know. We have discussed how to create and manage reusable Terraform modules, how to integrate Terraform with CDK, how to use CDK pipelines for automatic infrastructure deployment, and some advanced Terraform features like workspaces and resource targeting. By mastering these techniques, you can become a proficient DevOps engineer and deliver infrastructure deployments efficiently.

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