iac-modern-patterns

---

name: iac-modern-patterns description: Skill: Modern IaC Patterns — Pulumi, AWS CDK, Bicep, cdktf

Skill: Modern IaC Patterns — Pulumi, AWS CDK, Bicep, cdktf

When to Activate

• Choosing between Pulumi, AWS CDK, Terraform, or Bicep for a new project
• Writing Pulumi programs in TypeScript or Python
• Creating reusable AWS CDK Constructs (L2 or L3)
• Testing infrastructure code (unit tests, compliance tests)
• Designing multi-environment IaC strategy
• Migrating from Terraform DSL to a real programming language

---

Why Modern IaC? (vs Terraform HCL)

Capability	Terraform HCL	Pulumi / CDK
Real programming language	❌	✅
Loops & conditionals	⚠️ for_each, count	✅ Native
Unit testing	❌	✅
Type safety	❌	✅ (TypeScript)
IDE autocomplete	❌	✅
Reusable abstractions	Modules (limited)	Classes / Components
Multi-cloud	✅	✅ (Pulumi) / ❌ (CDK = AWS only)
Existing provider ecosystem	✅ Largest	✅ (Pulumi) / ⚠️ (CDK)

When to use Terraform still: large multi-cloud org with existing HCL expertise, team prefers DSL simplicity, need Terraform Cloud governance features.

---

Pulumi — Infrastructure as Real Code

Core Concepts

// index.ts — `pulumi up` diffs desired vs current state, then applies
import * as pulumi from "@pulumi/pulumi";
import * as aws from "@pulumi/aws";

const config = new pulumi.Config();
const environment = config.require("environment");  // dev / staging / prod
const dbInstanceClass = config.get("dbInstanceClass")
  ?? (environment === "prod" ? "db.t3.large" : "db.t3.micro");

const bucket = new aws.s3.Bucket("uploads", {
  bucket: `myapp-uploads-${environment}`,
  versioning: { enabled: true },
  serverSideEncryptionConfiguration: {
    rule: { applyServerSideEncryptionByDefault: { sseAlgorithm: "AES256" } },
  },
  tags: { Environment: environment, ManagedBy: "pulumi" },
});

export const bucketName = bucket.bucket;
export const bucketArn  = bucket.arn;

// Async outputs — use pulumi.interpolate / pulumi.all instead of string templates
const url = pulumi.interpolate`https://${bucket.bucketDomainName}/uploads`;
const conn = pulumi.all([db.endpoint, db.name, dbPassword]).apply(
  ([ep, name, pw]) => `postgresql://app:${pw}@${ep}:5432/${name}`
);

Stack Management

pulumi stack init dev && pulumi stack init prod
pulumi config set environment dev
pulumi config set aws:region eu-west-1
pulumi config set --secret dbPassword "$(openssl rand -base64 32)"
pulumi preview     # like terraform plan
pulumi up          # deploy
pulumi stack select prod

ComponentResource — Reusable Abstractions

// components/WebService.ts
export class WebService extends pulumi.ComponentResource {
  public readonly url: pulumi.Output<string>;

  constructor(name: string, args: { image: string; port: number; desiredCount?: number },
              opts?: pulumi.ComponentResourceOptions) {
    super("myapp:index:WebService", name, {}, opts);

    const cluster = new aws.ecs.Cluster(`${name}-cluster`, {}, { parent: this });
    const lb      = new awsx.lb.ApplicationLoadBalancer(`${name}-lb`, {}, { parent: this });
    const service = new awsx.ecs.FargateService(`${name}-svc`, {
      cluster: cluster.arn,
      taskDefinitionArgs: {
        container: { name, image: args.image, : , : ,
          : [{ : args. }] },
      },
      : args. ?? ,
      : [{ : lb..,
        : name, : args. }],
    }, { :  });

    . = lb...( );
    .({ : . });
  }
}

 api =  (, { : , :  });
  apiUrl = api.;

CrossGuard Policies

import { PolicyPack, validateResourceOfType } from "@pulumi/policy";
import * as aws from "@pulumi/aws";

new PolicyPack("aws-policies", {
  policies: [{
    name: "s3-no-public-access",
    enforcementLevel: "mandatory",
    validateResource: validateResourceOfType(aws.s3.Bucket, (bucket, _args, reportViolation) => {
      if (bucket.acl === "public-read" || bucket.acl === "public-read-write")
        reportViolation("S3 bucket must not be public");
    }),
  }, {
    name: "require-tags",
    enforcementLevel: "mandatory",
    validateResource: (args, reportViolation) => {
      const tags = args.props.tags ?? {};
      if (!tags.Environment) reportViolation("Missing tag: Environment");
      if (!tags.ManagedBy)   reportViolation("Missing tag: ManagedBy");
    },
  }],
});

---

AWS CDK — Infrastructure as TypeScript / Python

Core Concepts: App → Stack → Construct

App
└── Stack (prod, us-east-1)
    ├── VpcConstruct (L2 — sensible defaults)
    ├── EcsServiceConstruct (L3 — your reusable pattern)
    └── DatabaseConstruct (L3 — your reusable pattern)

Construct levels: L1 = raw CloudFormation wrappers, L2 = sane defaults + IAM helpers, L3 = your organisation's opinionated patterns.

L2 Constructs — Sane Defaults

import * as cdk from "aws-cdk-lib";
import * as s3 from "aws-cdk-lib/aws-s3";
import * as ec2 from "aws-cdk-lib/aws-ec2";
import * as ecs from "aws-cdk-lib/aws-ecs";
import * as ecs_patterns from "aws-cdk-lib/aws-ecs-patterns";
import { Construct } from "constructs";

export class AppStack extends cdk.Stack {
  constructor(scope: Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const bucket = new s3.Bucket(this, "Uploads", {
      versioned: true,
      encryption: s3.BucketEncryption.S3_MANAGED,
      blockPublicAccess: s3.BlockPublicAccess.BLOCK_ALL,
      removalPolicy: cdk..,
    });

     vpc =  ec2.(, , { : , :  });

     service =  ecs_patterns.(, , {
      vpc,
      : ,
      : ,
      : ,
      : {
        : ecs..(),
        : ,
        : { :  },
      },
    });

    bucket.(service..);
  }
}

L3 Constructs — Reusable Patterns

// constructs/WebService.ts
export interface WebServiceProps {
  vpc: ec2.IVpc;
  image: string;
  port: number;
  cpu?: number;
  memoryMiB?: number;
  desiredCount?: number;
  environment?: Record<string, string>;
}

export class WebService extends Construct {
  public readonly service: ecs_patterns.ApplicationLoadBalancedFargateService;
  public readonly url: string;

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

    this.service = new ecs_patterns.ApplicationLoadBalancedFargateService(this, "Service", {
      vpc: props.vpc,
      cpu: props.cpu ?? 256,
      : props. ?? ,
      : props. ?? ,
      : {
        : ecs..(props.),
        : props.,
        : props.,
        
      },
    });

    . = ;
  }
}

CDK Aspects — Cross-Cutting Compliance

// Enforce encryption on every S3 bucket in the app tree
export class RequireEncryption implements cdk.IAspect {
  public visit(node: IConstruct): void {
    if (node instanceof s3.CfnBucket && !node.bucketEncryption)
      cdk.Annotations.of(node).addError("S3 bucket must have encryption configured");
  }
}

cdk.Aspects.of(app).add(new RequireEncryption());

CDK Unit Testing

import { Template, Match } from "aws-cdk-lib/assertions";

const template = Template.fromStack(new AppStack(new App(), "Test"));

template.hasResourceProperties("AWS::S3::Bucket", {
  VersioningConfiguration: { Status: "Enabled" },
  PublicAccessBlockConfiguration: { BlockPublicAcls: true, RestrictPublicBuckets: true },
});

const services = template.findResources("AWS::ECS::Service");
const minCount = Math.min(...Object.values(services).map((s: any) => s.Properties.DesiredCount));
expect(minCount).toBeGreaterThanOrEqual(2);

---

Azure Bicep

// main.bicep
param environment string = 'dev'
param location string = resourceGroup().location

var storageAccountName = 'myapp${environment}${uniqueString(resourceGroup().id)}'

resource storageAccount 'Microsoft.Storage/storageAccounts@2023-01-01' = {
  name: storageAccountName
  location: location
  sku: {
    name: environment == 'prod' ? 'Standard_ZRS' : 'Standard_LRS'
  }
  kind: 'StorageV2'
  properties: {
    minimumTlsVersion: 'TLS1_2'
    supportsHttpsTrafficOnly: true
    allowBlobPublicAccess: false
  }
}

output storageAccountName string = storageAccount.name
output storageAccountId string = storageAccount.id

# Deploy Bicep
az deployment group create \
  --resource-group myapp-prod \
  --template-file main.bicep \
  --parameters environment=prod

---

CDK for Terraform (cdktf)

Use when you need Terraform providers (non-AWS) but want TypeScript/Python instead of HCL.

// main.ts
import { App, TerraformStack, TerraformOutput } from "cdktf";
import { AwsProvider } from "@cdktf/provider-aws/lib/provider";
import { S3Bucket } from "@cdktf/provider-aws/lib/s3-bucket";

class MyStack extends TerraformStack {
  constructor(scope: Construct, id: string) {
    super(scope, id);

    new AwsProvider(this, "AWS", { region: "eu-west-1" });

    const bucket = new S3Bucket(this, "uploads", {
      bucket: "myapp-uploads-prod",
      versioning: { enabled: true },
      tags: { Environment: "prod", ManagedBy: "cdktf" },
    });

    new TerraformOutput(this, "bucket_name", { value: bucket. });
  }
}

 app =  ();
 (app, );
app.();

cdktf deploy    # terraform apply equivalent
cdktf destroy   # terraform destroy equivalent
cdktf synth     # generate Terraform JSON config

---

Multi-Environment Strategy

Pulumi: Configuration per Stack

# dev stack
pulumi config set --stack dev environment dev
pulumi config set --stack dev instanceType t3.micro
pulumi config set --stack dev desiredCount 1

# prod stack
pulumi config set --stack prod environment prod
pulumi config set --stack prod instanceType t3.large
pulumi config set --stack prod desiredCount 3

// index.ts — single program, multiple stack configs
const config = new pulumi.Config();
const environment = config.require("environment");
const instanceType = config.get("instanceType") ?? "t3.micro";
const desiredCount = config.getNumber("desiredCount") ?? 1;

// All resources automatically namespaced by stack

CDK: Environments per Stack

// bin/app.ts
const app = new cdk.App();

new AppStack(app, "Dev", {
  env: { account: "111111111", region: "eu-west-1" },
  instanceType: "t3.micro",
  desiredCount: 1,
});

new AppStack(app, "Prod", {
  env: { account: "222222222", region: "eu-west-1" },
  instanceType: "t3.large",
  desiredCount: 3,
});

---

IaC Security & Compliance

OPA/Conftest Against Generated Templates

# CDK: test generated CloudFormation
cdk synth > /tmp/template.json
conftest test /tmp/template.json --policy policy/

# Pulumi: test generated resources
pulumi preview --json | conftest test - --policy policy/

# policy/s3.rego
package main

deny[msg] {
  resource := input.Resources[_]
  resource.Type == "AWS::S3::Bucket"
  not resource.Properties.BucketEncryption
  msg := sprintf("S3 bucket '%v' must have encryption configured", [resource])
}

Infrastructure Drift Detection

# Pulumi: detect drift
pulumi refresh --expect-no-changes

# CDK: detect drift (via CloudFormation)
aws cloudformation detect-stack-drift --stack-name MyStack
aws cloudformation describe-stack-drift-detection-status --stack-drift-detection-id DETECTION_ID

---

Publish CDK Constructs to Construct Hub

// .projenrc.ts (using projen)
import { awscdk } from "projen";

const project = new awscdk.AwsCdkConstructLibrary({
  author: "Your Name",
  authorAddress: "[e-mail]",
  cdkVersion: "2.0.0",
  defaultReleaseBranch: "main",
  name: "@myorg/web-service-construct",
  repositoryUrl: "https://github.com/myorg/web-service-construct",
  // Automatically publishes to npm, PyPI, Maven, NuGet
  publishToNpm: true,
  publishToPypi: { distName: "myorg.web-service-construct", module: "myorg_web_service_construct" },
});

project.synth();

---

Related Skills

• terraform-patterns — Terraform HCL patterns with cross-reference to when to choose Pulumi/CDK
• kubernetes-patterns — deploying to Kubernetes with Pulumi/CDK generated manifests
• devsecops-patterns — OPA/Conftest integration into IaC CI pipeline
• ci-cd-patterns — GitHub Actions for IaC deployment pipelines