pulumi-cdk-to-pulumi — Claude Code skill: move AWS CDK to Pulumi

---
name: pulumi-cdk-to-pulumi
description: Load this skill when a user wants to migrate, convert, port, translate, or move an AWS CDK application (including CDK stacks, constructs, or CloudFormation-synthesized templates) to Pulumi. Phrases such as "convert CDK to Pulumi", "migrate CDK app", "port CDK stacks", "replace CDK with Pulumi", "stop using CDK". Do NOT load for general CDK questions, CDK-only help, or CDK vs Pulumi comparisons where no migration is requested.
---

# CRITICAL SUCCESS REQUIREMENTS

The migration output MUST meet all of the following:

1. **Complete Resource Coverage**
   - Every CloudFormation resource synthesized by CDK MUST:
     - Be represented in the Pulumi program **OR**
     - Be explicitly justified in the final report.

2. **Successful Deployment**
   - The produced Pulumi program must be structurally valid and capable of a successful `pulumi up` (assuming proper config).

3. **Final Migration Report**
   - Always output a formal migration report suitable for a Pull Request.
   - Include:
     - CDK → Pulumi resource mapping
     - Provider decisions (aws-native vs aws)
     - Behavioral differences
     - Missing or manually required steps
     - Validation instructions

## WHEN INFORMATION IS MISSING

If a user-provided CDK project is incomplete, ambiguous, or missing artifacts (such as `cdk.out`), ask **targeted questions** before generating Pulumi code.

## MIGRATION WORKFLOW

Follow this workflow **exactly** and in this order:

### 1. INFORMATION GATHERING

#### 1.1 Verify AWS Credentials (ESC)

Running AWS commands (e.g., `aws cloudformation list-stack-resources`) and CDK commands (e.g. `cdk synth`) requires credentials loaded via Pulumi ESC.

- If the user has already provided an ESC environment, use it.
- If no ESC environment is specified, **ask the user which ESC environment to use** before proceeding with AWS commands.

You MUST confirm the AWS region with the user. The `cdk synth` results may be incorrect if ran with the wrong AWS Region.

#### 1.2 Synthesize CDK

Run/inspect:

```bash
npx cdk synth --quiet
```

- ALWAYS run `synth` with `--quiet` to prevent the template from being output on stdout.

If failing, inspect `cdk.json` or `package.json` for custom synth behavior.

#### 1.3 Identify CDK Stacks & Environments

Read `cdk.out/manifest.json`:

```bash
jq '.artifacts | to_entries | map(select(.value.type == "aws:cloudformation:stack") | {displayName: .key, environment: .value.environment}) | .[]' cdk.out/manifest.json
```

Example output:

```json
{
  "displayName": "DataStack-dev",
  "environment": "aws://616138583583/us-east-2"
}
{
  "displayName": "AppStack-dev",
  "environment": "aws://616138583583/us-east-2"
}
```

In the Pulumi stack you create you MUST set both the `aws:region` and `aws-native:region` config variables. For example:

```bash
pulumi config set aws-native:region us-east-2 --stack dev
pulumi config set aws:region us-east-2 --stack dev
```

#### 1.4 Build Resource Inventory

For each stack:

```bash
aws cloudformation list-stack-resources \
  --region <region> \
  --stack-name <stack> \
  --output json
```

#### 1.5 Analyze CDK Structure

Extract:

- Environment-specific conditionals
- Stack dependencies & cross-stack references
- Runtime config (context/env vars)
- Construct types (L1, L2, L3)

### 2. CODE CONVERSION (CDK → PULUMI)

- Perform the initial conversion using the `cdk2pulumi` tool. Follow [cdk-convert.md](cdk-convert.md) to perform the conversion.
- Read the conversion report and fill in any gaps. For example, if the conversion fails to convert a resource you have to convert it manually yourself.

#### 2.1 Custom Resources Handling

CDK uses Lambda-backed Custom Resources for functionality not available in CloudFormation. In synthesized CloudFormation, these appear as:

- Resource type: `AWS::CloudFormation::CustomResource` or `Custom::<name>`
- Metadata contains `aws:cdk:path` with the handler name (e.g., `aws-s3/auto-delete-objects-handler`)

**Default behavior**: `cdk2pulumi` rewrites custom resources to `aws-native:cloudformation:CustomResourceEmulator`, which invokes the original Lambda. This works but has tradeoffs (Lambda dependency, cold starts, eventual consistency).

**Migration strategies by handler type:**

| Handler | Strategy |
|---------|----------|
| `aws-certificatemanager/dns-validated-certificate-handler` | Replace with `aws.acm.Certificate`, `aws.route53.Record`, and `aws.acm.CertificateValidation` |
| `aws-ec2/restrict-default-security-group-handler` | Replace with `aws.ec2.DefaultSecurityGroup` resource with empty ingress/egress rules |
| `aws-ecr/auto-delete-images-handler` | Replace `aws-native:ecr:Repository` with `aws.ecr.Repository` with `forceDelete: true` |
| `aws-s3/auto-delete-objects-handler` | Replace `aws-native:s3:Bucket` with `aws.s3.Bucket` with `forceDestroy: true` |
| `aws-s3/notifications-resource-handler` | Replace with `aws.s3.BucketNotification` |
| `aws-logs/log-retention-handler` | Replace with `aws.cloudwatch.LogGroup` with explicit `retentionInDays` |
| `aws-iam/oidc-handler` | Replace with `aws.iam.OpenIdConnectProvider` |
| `aws-route53/delete-existing-record-set-handler` | Replace with `aws.route53.Record` with `allowOverwrite: true` |
| `aws-dynamodb/replica-handler` | Replace with `aws.dynamodb.TableReplica` |

**Cross-account/region handlers:**

- `aws-cloudfront/edge-function` → Use `aws.lambda.Function` with `region: "us-east-1"`
- `aws-route53/cross-account-zone-delegation-handler` → Use separate aws provider with cross-account role assumption

**Graceful degradation for unknown handlers:**

1. Keep the `CustomResourceEmulator` (default behavior)
2. Document the custom resource in the migration report with:
   - Original handler name and purpose (if discernible from CDK path)
   - Note that it uses Lambda invocation at runtime
   - Recommend user review for potential native replacement

#### 2.2 Provider Strategy

- **Default**: Use `aws-native` whenever the resource type is available.
- **Fallback**: Use `aws` when aws-native does not support equivalent features.

#### 2.3 Assets & Bundling

CDK uses Assets and Bundling to handle deployment artifacts. These are processed by the CDK CLI before CloudFormation deployment and appear in the `cdk.out` directory alongside `*.assets.json` metadata files. CloudFormation templates contain hard-coded references to asset locations (S3 bucket/key or ECR repo/tag).

```bash
# Inspect asset definitions
jq '.files, .dockerImages' cdk.out/*.assets.json
```

**Migration strategies by asset type:**

| Asset Type | Detection | Pulumi Migration |
|------------|-----------|------------------|
| **Docker Image** | `dockerImages` in assets.json | Use `docker-build.Image` to build and push. Replace hard-coded ECR URI with image output. |
| **File with build command** | `files` with `executable` field | **Flag to user** - build command needs setup in Pulumi |
| **Static file** | `files` without `executable`, no bundling in CDK source | Use `pulumi.FileArchive` or `pulumi.FileAsset` |
| **Bundled file** | `files` without `executable`, but CDK source uses bundling | **Flag to user** - bundling needs setup in Pulumi |

**Detecting Bundling in CDK Source:**

Check the CDK source code for bundling constructs (`NodejsFunction`, `PythonFunction`, `GoFunction`, or resources using the `bundling` option). If bundling is used, the build step needs to be replicated in Pulumi for ongoing development - otherwise source changes would require manually re-running `cdk synth`.

**When bundling is detected, inform the user:**

> **Build Step Detected**: This CDK application uses <BUNDLING_TYPE> which builds deployable artifacts during synthesis. This build step needs to be replicated in Pulumi for ongoing development.
>
> **Options:**
>
> 1. **CI/CD Pipeline** (Recommended): Move the build step to your CI pipeline and reference the pre-built artifact in Pulumi
> 2. **Pulumi Command Provider**: Use `command.local.Command` to run the build command during `pulumi up`
> 3. **Pre-build Script**: Create a build script that runs before `pulumi up` and outputs to a known location
>
> Each option has tradeoffs around caching, reproducibility, and deployment speed. For production workloads, option 1 is typically preferred.

#### 2.4 TypeScript Handling for aws-native

aws-native outputs often include undefined. Avoid `!` non-null assertions. Always safely unwrap with `.apply()`:

```ts
// ❌ WRONG - Will cause TypeScript errors
functionName: lambdaFunction.functionName!,

// ✅ CORRECT - Handle undefined safely
functionName: lambdaFunction.functionName.apply(name => name || ""),
```

#### 2.5 Environment Logic Preservation

Carry forward all conditional behaviors:

```ts
if (currentEnv.createVpc) {
  // create resources
} else {
  const vpcId = pulumi.output(currentEnv.vpcId);
}
```

### 3. Resource Import (optional)

After conversion you can optionally import the existing resources to now be managed by Pulumi. If the user does not request this you should suggest this as a follow up step to conversion.

- Always start with automated import using the `cdk-importer` tool. Follow [cdk-importer.md](cdk-importer.md) to perform the automated import.
- For any resources that fail to import with the automated tool, import them manually.

If you need to manually import resources:

- Follow [cloudformation-id-lookup.md](cloudformation-id-lookup.md) to look up CloudFormation import identifiers.
- Use the web-fetch tool to get content from the official Pulumi documentation.

- **Finding AWS import IDs** -> <https://www.pulumi.com/docs/iac/guides/migration/aws-import-ids/>
- **Manual migration approaches** -> <https://www.pulumi.com/docs/iac/guides/migration/migrating-to-pulumi/migrating-from-cdk/migrating-existing-cdk-app/#approach-b-manual-migration>

#### 3.1 Running preview after import

After performing an import you need to run `pulumi preview` to ensure there are no changes. No changes means:

- NO updates
- NO replaces
- NO creates
- NO deletes

If there are changes you must investigate and update the program until there are no changes.

## Working with the User

If the user asks for help planning or performing a CDK to Pulumi migration use the information above to guide the user towards the automated migration approach.

## For Detailed Documentation

When the user wants to deviate from the recommended path detailed above, use the web-fetch tool to get content from the official Pulumi documentation -> <https://www.pulumi.com/docs/iac/guides/migration/migrating-to-pulumi/migrating-from-cdk/migrating-existing-cdk-app>

This documentation covers topics:

- Migration Strategy
  - Convert vs. Rewrite
  - Import vs. Rehydrate
  - Best Practices
- Handling Multiple CDK Stacks
- Handling CDK Stages
- Code organization
- Converting CDK Constructs
- Execution Strategies
  - Automated Migration (recommended)
  - Manual Migration

## OUTPUT FORMAT (REQUIRED)

When performing a migration, always produce:

1. **Overview** (high-level description)
2. **Migration Plan Summary**
3. **Pulumi Code Outputs** (TypeScript; structured by file)
4. **Resource Mapping Table** (CDK → Pulumi)
5. **Custom Resources Summary** (if any):
   - Handlers migrated to native Pulumi resources
   - Handlers kept as `CustomResourceEmulator` with rationale
   - Any handlers requiring user attention
6. **Assets & Bundling Summary** (if any):
   - **Migrated**: Assets successfully converted (e.g., Docker images → `docker-build.Image`, static files → `pulumi.FileArchive`)
   - **Requires attention**: Assets with bundling steps, options presented, and decision if made
7. **Final Migration Report** (PR-ready)
8. **Next Steps** (optional refactors)

Keep code syntactically valid and clearly separated by files.