CI/CD for Infrastructure: Exploring AWS CDK Pipelines

Running cdk deploy from your local machine is fine for development, but for production, you need a robust, automated CI/CD pipeline. The AWS CDK comes with its own high-level construct library for this purpose: CDK Pipelines.

CDK Pipelines is an opinionated construct that makes it incredibly easy to create a CI/CD pipeline that builds, tests, and deploys your CDK application. The best part? The pipeline is self-mutating. If you push a change to the pipeline's definition itself, the pipeline will automatically update and redeploy.

The Core Concepts

A CDK Pipeline is built on top of several other AWS services:

• AWS CodeCommit (or GitHub/Bitbucket): The Git repository that holds your CDK application code.
• AWS CodeBuild: The service that runs the build and synthesis steps (e.g., npm install, npm run build, cdk synth).
• AWS CodePipeline: The orchestrator that defines the stages of your pipeline (Source, Build, Deploy, etc.).

CDK Pipelines abstracts away most of the complexity of wiring these services together.

Building a Simple Pipeline

Let's create a pipeline that deploys a simple Lambda stack.

Prerequisites: Your CDK application code must be in a Git repository (we'll use CodeCommit in this example).

1. Create a Pipeline Stack: It's a best practice to define your pipeline in a separate stack from your application stacks.

   // lib/pipeline-stack.ts
   import { Stack, StackProps } from 'aws-cdk-lib';
   import { Construct } from 'constructs';
   import { CodePipeline, CodePipelineSource, ShellStep } from 'aws-cdk-lib/pipelines';
   import * as codecommit from 'aws-cdk-lib/aws-codecommit';
   
   export class MyPipelineStack extends Stack {
     constructor(scope: Construct, id: string, props?: StackProps) {
       super(scope, id, props);
   
       const repo = codecommit.Repository.fromRepositoryName(this, 'MyRepo', 'my-cdk-app-repo');
   
       const pipeline = new CodePipeline(this, 'MyPipeline', {
         pipelineName: 'MyAppPipeline',
         synth: new ShellStep('Synth', {
           input: CodePipelineSource.codeCommit(repo, 'main'),
           commands: [
             'npm ci',       // Install dependencies
             'npm run build',  // Compile TypeScript
             'npx cdk synth',// Synthesize CloudFormation
           ],
         }),
       });
     }
   }
   

2. Define an Application Stage: A "stage" in a CDK Pipeline is a deployable unit that typically contains one or more application stacks. You'll define this in a separate file.

   // lib/my-app-stage.ts
   import { Stage, StageProps } from 'aws-cdk-lib';
   import { Construct } from 'constructs';
   import { MyLambdaStack } from './my-lambda-stack'; // Your application stack
   
   export class MyAppStage extends Stage {
     constructor(scope: Construct, id: string, props?: StageProps) {
       super(scope, id, props);
   
       new MyLambdaStack(this, 'MyLambdaStack');
     }
   }
   

3. Add the Stage to the Pipeline: Now, you add an instance of your MyAppStage to the pipeline.

   // In lib/pipeline-stack.ts, inside the constructor
   
   // ... after defining the pipeline
   
   pipeline.addStage(new MyAppStage(this, 'Deploy-Dev', {
     env: { account: '111122223333', region: 'us-east-1' },
   }));
   

How it Works

• input: The CodePipelineSource points to the main branch of your CodeCommit repository. Any push to this branch will trigger the pipeline.
• synth: This is the build step. The ShellStep defines the commands that CodePipeline will run to install dependencies, build your code, and synthesize the CloudFormation templates (cdk synth). The output of this step is a cdk.out directory, which is a Cloud Assembly artifact.
• addStage: This adds a deployment stage to the pipeline. The pipeline will take the Cloud Assembly from the synth step and deploy the stacks defined in MyAppStage to the specified environment.

Adding More Stages (e.g., Staging and Production)

The real power comes from adding multiple stages. You can create a deployment process that promotes your code through different environments.

// In lib/pipeline-stack.ts

const devStage = new MyAppStage(this, 'Dev', {
  env: { account: '111122223333', region: 'us-east-1' },
});

pipeline.addStage(devStage);

pipeline.addStage(new MyAppStage(this, 'Prod', {
  env: { account: '444455556666', region: 'us-west-2' },
}), {
  // Add a manual approval step before deploying to production
  pre: [new ManualApprovalStep('PromoteToProd')],
});

In this example:

1. The code is automatically deployed to the Dev environment.
2. The pipeline then pauses at a manual approval step.
3. An administrator must go into the CodePipeline console and approve the change before the same code is deployed to the Prod environment.

Conclusion

CDK Pipelines provides a high-level abstraction that dramatically simplifies the process of creating robust, self-mutating CI/CD pipelines for your infrastructure. By defining your pipeline in the same language as your application and infrastructure, you create a unified, powerful, and maintainable system for automating your deployments. It's the standard, recommended way to ship CDK applications to production.