pulumi-cdk-to-pulumi

SKILL.md

CRITICAL SUCCESS REQUIREMENTS

The migration output MUST meet all of the following:

Complete Resource Coverage

Every CloudFormation resource synthesized by CDK MUST:

Be represented in the Pulumi program OR

Be explicitly justified in the final report.

Successful Deployment

The produced Pulumi program must be structurally valid and capable of a successful pulumi up (assuming proper config).

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:

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:

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

Example output:

{
  "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:

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:

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 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:

Keep the CustomResourceEmulator (default behavior)

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).

# 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:

CI/CD Pipeline (Recommended): Move the build step to your CI pipeline and reference the pre-built artifact in Pulumi

Pulumi Command Provider: Use command.local.Command to run the build command during pulumi up

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():

// ❌ 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:

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 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 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:

Overview (high-level description)

Migration Plan Summary

Pulumi Code Outputs (TypeScript; structured by file)

Resource Mapping Table (CDK → Pulumi)

Custom Resources Summary (if any):

Handlers migrated to native Pulumi resources

Handlers kept as CustomResourceEmulator with rationale

Any handlers requiring user attention

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

Final Migration Report (PR-ready)

Next Steps (optional refactors)

Keep code syntactically valid and clearly separated by files.