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Crossplane Function Template - TypeScript

This repository is a template for building Crossplane composition functions in TypeScript using the @crossplane-org/function-sdk-typescript.

Overview

This template provides a full Typescript project for developing Crossplane functions that can transform, validate, and generate Kubernetes resources within Crossplane compositions.

The initial src/function.ts creates sample Deployment, Ingress, Service, and ServiceAccount resources and can be customized to create any type of Kubernetes resource.

For an example of configuring cloud resources, refer to configuration-aws-network-ts.

Running the Example Package

The configuration and function are published to the Upbound Marketplace, and can be installed into a Crossplane environment.

Installing the Package

The Configuration package will install the function package, which contains a Node docker image and the source code as a dependency.

apiVersion: pkg.crossplane.io/v1
kind: Configuration
metadata:
  name: configuration-template-typescript
spec:
  package: xpkg.upbound.io/function-template-typescript:v0.1.0

Once installed, confirm that the package and dependencies are installed:

crossplane beta trace con
figuration.pkg configuration-template-typescript
NAME                                                                              VERSION          INSTALLED   HEALTHY   STATE    STATUS
Configuration/configuration-template-typescript                                   v0.1.0   True        True      -        HealthyPackageRevision
├─ ConfigurationRevision/configuration-template-typescript-93b73b00eb21           v0.1.0   -           -         Active
├─ Function/crossplane-contrib-function-auto-ready                                v0.6.0           True        True      -        HealthyPackageRevision
│  └─ FunctionRevision/crossplane-contrib-function-auto-ready-59868730b9a9        v0.6.0           -           -         Active
└─ Function/upbound-function-template-typescript-function                           v0.1.0   True        True      -        HealthyPackageRevision
   └─ FunctionRevision/upbound-function-template-typescript-function-cd83fe939bc7   v0.1.0   -

Deploy the Example Manifest

Once the package is installed and healthy, create the target namespace and install the example:

$ kubectl apply -f examples/app/ns.yaml
namespace/example created

$ kubectl apply -f examples/apps/example.yaml
app.platform.upbound.io/hello-app created

Validate the Example is running

Use crossplane beta trace to validate the Composition:

crossplane beta trace -n example app.platform.upbound.io/hello-app
NAME                                             SYNCED   READY   STATUS
App/hello-app (example)                          True     True    Available
├─ Deployment/hello-app-7ff730da5be9 (example)   -        -
├─ ServiceAccount/my-service-account (example)   -        -
└─ Service/hello-app-ab25df85445e (example)      -        -

Next, examine the resources in the namespace:

kubectl get all,sa -n example -l app.kubernetes.io/instance=hello-app
NAME                                          READY   STATUS    RESTARTS   AGE
pod/hello-app-7ff730da5be9-76975c8c4c-mth2n   1/1     Running   0          5m36s

NAME                             TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)    AGE
service/hello-app-ab25df85445e   ClusterIP   10.96.153.148   <none>        8080/TCP   5m36s

NAME                                     READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/hello-app-7ff730da5be9   1/1     1            1           5m36s

NAME                                                DESIRED   CURRENT   READY   AGE
replicaset.apps/hello-app-7ff730da5be9-76975c8c4c   1         1         1       5m36s

NAME                                SECRETS   AGE
serviceaccount/my-service-account   0         5m36s

Change the settings in examples/apps/example.yaml and observe the generated resources.

Development Prerequisites

To develop Compositions using Typescript, the following is recommended:

  • Node.js 24 or later recommended.
  • npm
  • Docker (for building the Node container image)
  • Both TypeScript 5+ and TypeScript 7 (tsgo) are supported.

Project Structure

.
├── src/                          # Source files
│   ├── function.ts               # Main function implementation
│   ├── function.test.ts          # Function tests
│   ├── test-helpers.ts           # Test utilities for loading YAML test cases
│   └── main.ts                   # Entry point and server setup
├── test-cases/                   # YAML-based test cases
│   ├── README.md                 # Test case documentation
│   └── example.yaml              # Example test case
├── examples/                     # Example Crossplane resources
│   ├── apps/                     # Example application resources
│   └── functions.yaml            # Function pipeline configuration
├── scripts/                      # Build and deployment scripts
│   ├── function-docker-build.sh
│   ├── function-xpkg-build.sh
│   ├── function-xpkg-push.sh
│   ├── configuration-xpkg-build.sh
│   └── configuration-xpkg-push.sh
├── package-configuration/        # Configuration package metadata
│   ├── apis                      # Crossplane Composition Files
│   │   └── apps                  # Directory for the Kubernetes App Kind
│   │       ├── composition.yaml  # Crossplane Composition Pipeline Definition
│   │       └── definition.yaml   # Crossplane CompositeResourceDefinition
│   └── crossplane.yaml           # Configuration package manifest
├── package-function/             # Function package metadata
│   └── crossplane.yaml           # Function package manifest
├── dist/                         # Compiled JavaScript output (generated)
├── _build/                       # Build artifacts (generated)
├── package.json                  # Dependencies and scripts
├── tsconfig.json                 # TypeScript configuration
├── tsconfig.eslint.json          # TypeScript ESLint configuration
├── jest.config.js                # Jest test configuration
├── eslint.config.js              # ESLint configuration
├── env                           # Environment variables for build scripts
└── Dockerfile                    # Container image definition

Installation

  1. Clone this repository
  2. Install dependencies:
npm install

Development

Build TypeScript

Compile TypeScript to JavaScript using TypeScript 5:

npm run tsc

TypeScript 7 (tsgo) is the default engine for the build:

npm run build
# or
npm run tsgo

Type Checking

Check types without emitting files:

npm run check-types

Testing

Run tests using Jest:

npm test

TypeScript tests are written in src/function.test.ts. YAML-based test cases can be created using the test-cases/ directory. See test-cases/README.md for more information on creating tests. Example Crossplane resources for testing are provided in the examples/ directory.

Linting and Formatting

The project includes ESLint and Prettier for code quality:

# Lint code
npm run lint

# Auto-fix linting issues
npm run lint:fix

# Format code with Prettier
npm run format

# Check formatting without changing files
npm run format:check

Running Locally

Run the function server in insecure mode for local testing:

npm run local
# or
node dist/main.js --insecure --debug

Once the function is running locally, crossplane render can be used to render examples:

crossplane render examples/app/example.yaml package-configuration/apis/apps/composition.yaml examples/functions.yaml

Available CLI Options

  • --address - Address to listen for gRPC connections (default: 0.0.0.0:9443)
  • -d, --debug - Enable debug logging
  • --insecure - Run without mTLS credentials (for local development)
  • --tls-server-certs-dir - Directory containing mTLS certificates (default: /tls/server)

Building and Packaging

Crossplane Packages are used to deploy the Function and and dependencies to a Crossplane environment. Each of the package types serves a distinct purpose:

  • Configuration Packages contain the API (Composite Resource Definition) and Composition (Pipeline Steps). Configuration packages can pull in other packages types as dependencies.
  • The Function Package contains the TypeScript files bundled in a runnable Node Docker container.
  • Optional Packages that contain support for managing external APIs like GCP, AWS, and Azure.
flowchart LR
    subgraph CP [Configuration Package]
    XRD(CompositeResourceDefinition XRD)
    C(Composition)
    end
    CP -->|dependsOn| FP
    subgraph FP [Function Package]
    ED[Embedded Docker image]
    end
    CP -->|dependsOn| Providers
    subgraph Providers [Optional Providers]
    AWS[provider-upjet-aws]
    SQL[provider-sql]
    end
Loading

Local Docker Build

This template repository includes Github Actions for building and pushing the images.

Scripts are provided that can also be run via npm to build and publish packages.

To build the docker image run:

npm run function-docker-build

The images will be saved as tar files that can be packed into a Function Package:

tree _build/docker_images
_build/docker_images
├── function-template-typescript-function-runtime-amd64-v0.1.0.tar
└── function-template-typescript-function-runtime-arm64-v0.1.0.tar

The Dockerfile uses a multi-stage build:

  1. Build stage: Uses node:24 (LTS) to install dependencies and compile TypeScript
  2. Runtime stage: Uses gcr.io/distroless/nodejs24-debian12 for a minimal, secure runtime that includes the compiled TypeScript source.

Refer to the scripts directory for examples of multi-platform builds.

Build the Crossplane Function Package

Now that runnable Docker images have been generated, they can be embedded into a Function package.

Update the Function Package Metadata

First Update the Function Package crossplane.yaml to the name of the Function.

Update the metadata.name and metadata.annotations in the crossplane.yaml file.

Building the Function Package

Build the function as a Crossplane package (xpkg):

# Build the function package
npm run function-xpkg-build

Function packages will be generated for arm64 and amd64 in the _build/xpkg directory:

$ tree _build/xpkg
_build/xpkg
├── function-template-typescript-function-amd64-v0.1.0.xpkg
└── function-template-typescript-function-arm64-v0.1.0.xpkg

These packages can be pushed to any Docker Registry using crossplane xpkg push. Update the XPKG_REPO in the env file to change the target repository.

# Push to a registry
npm run function-xpkg-push

# Build and push in one step
npm run function-build-all

Configuration Package

With the Function package created, the Configuration Package can be generated. This package will install the Function Package as a dependency.

Updating the crossplane.yaml File

First Update the Configuration Package crossplane.yaml to the name of the Configuration.

Update the metadata.name and metadata.annotations in the crossplane.yaml file.

Next update the spec.dependsOn field to include the function Docker image and any other dependencies, like function-auto-ready.

spec:
  dependsOn:
    - apiVersion: pkg.crossplane.io/v1
      kind: Function
      package: xpkg.upbound.io/crossplane-contrib/function-auto-ready
      version: '>=v0.6.0'
    # Make this match your function
    - apiVersion: pkg.crossplane.io/v1
      kind: Function
      package: xpkg.upbound.io/upbound/function-template-typescript-function
      version: '>=v0.1.0'

A Crossplane Composition requires a CompositeResourceDefinition (XRD) and Composite. These are located in the package-configuration/apis directory.

Since the Kind in the template function is an App, we create a subdirectory apps.

Update the composition.yaml file to have the functionRef of the first pipeline step to refer to the name of the function once it is installed. Crossplane creates a function name of <docker repository>-<function-name>, so xpkg.upbound.io/upbound/function-template-typescript-function would have a functionRef.name of upbound-function-template-typescript-function.

Update the value with the name that represents the Docker registry and image where the function was pushed.

- functionRef:
    name: upbound-function-template-typescript-function
  step: app

Build the Configuration Package

Build the Crossplane configuration package:

# Build configuration package
npm run configuration-xpkg-build

The _build/xpkg directory will contain the multi-platform function images and the Configuration package image:

tree _build/xpkg
_build/xpkg
├── function-template-typescript-function-amd64-v0.1.0.xpkg
├── function-template-typescript-function-arm64-v0.1.0.xpkg
└── function-template-typescript-v0.1.0.xpkg

Push this package to a Docker registry:

# Push configuration package
npm run configuration-xpkg-push

Local build scripts are located in the scripts/ directory and can be customized. Common settings are contained in the env file.

Implementation Guide

Creating Your Function

Edit src/function.ts to implement your function logic. The main interface is:

export class Function implements FunctionHandler {
  async RunFunction(req: RunFunctionRequest, logger?: Logger): Promise<RunFunctionResponse> {
    // Your function logic here
  }
}

Key SDK Functions

The SDK provides helper functions for working with Crossplane resources:

  • getObservedCompositeResource(req) - Get the observed composite resource (XR)
  • getDesiredCompositeResource(req) - Get the desired composite resource
  • getObservedComposedResources(req) - Get observed composed resources
  • getDesiredComposedResources(req) - Get desired composed resources
  • setDesiredComposedResources(rsp, resources) - Set desired composed resources
  • Resource.fromJSON() - Create resources from JSON
  • normal(rsp, message) - Add a normal condition to the response
  • fatal(rsp, message) - Add a fatal condition to the response
  • to(req) - Create a minimal response from a request

See src/function.ts for examples of using these SDK functions.

Example: Creating a Resource

import { Resource } from '@crossplane-org/function-sdk-typescript';

// Create from JSON
const resource = Resource.fromJSON({
  resource: {
    apiVersion: 'v1',
    kind: 'ConfigMap',
    metadata: {
      name: 'my-config',
      namespace: 'default',
    },
    data: {
      key: 'value',
    },
  },
});

// Add to desired composed resources
desiredComposed['my-config'] = resource;

Using Kubernetes Models

The template includes kubernetes-models for type-safe K8s resource creation:

import { Pod } from 'kubernetes-models/v1';

const pod = new Pod({
  metadata: {
    name: 'my-pod',
    namespace: 'default',
  },
  spec: {
    containers: [
      {
        name: 'app',
        image: 'nginx:latest',
      },
    ],
  },
});

pod.validate(); // Validate the resource

desiredComposed['my-pod'] = Resource.fromJSON({ resource: pod.toJSON() });

Testing Your Function

Create YAML test cases in the test-cases/ directory. Each test case defines:

  • Input: The observed composite resource and context
  • Expected: Resource counts, types, and validation rules

See test-cases/example.yaml for an example. Tests use src/test-helpers.ts to load and validate YAML test cases.

TypeScript Configuration

This template uses strict TypeScript settings:

  • strict: true - All strict type checking options
  • noUncheckedIndexedAccess: true - Safer array/object access
  • exactOptionalPropertyTypes: true - Stricter optional properties
  • verbatimModuleSyntax: true - Explicit import/export syntax

The SDK directory is excluded from compilation to avoid conflicts with different TypeScript settings.

GitHub Actions

This project includes automated CI/CD workflows in the .github/workflows/ directory:

CI Workflow (ci.yaml)

The main CI workflow runs automatically on:

  • Pushes to main or release-* branches
  • Pull requests
  • Manual dispatch with optional version override

Jobs:

  1. version - Computes the package version

    • Uses npm pkg get version from package.json
    • Generates pseudo-version: v{version}-{timestamp}-{git-sha} (e.g., v0.1.1-20231101115142-1091066df799)
    • Can be overridden with manual workflow dispatch input

  2. lint - Code quality checks

    • Runs npm run lint using ESLint
    • Validates code style and catches common errors

  3. test - Runs the test suite

    • Executes npm test with Jest
    • Validates function logic and YAML test cases

  4. check-types - TypeScript type checking

    • Runs npm run check-types
    • Ensures type safety without emitting files

  5. build-configuration-package - Builds the Crossplane configuration package

    • Uses Crossplane CLI to build the configuration from package-configuration/ directory
    • Uploads the configuration .xpkg as an artifact

  6. build-function-packages - Builds function packages for multiple architectures

    • Builds Docker images for both amd64 and arm64 architectures
    • Uses Docker Buildx with QEMU for cross-platform builds
    • Leverages GitHub Actions cache for faster builds
    • Embeds runtime images into Crossplane function packages (.xpkg)
    • Uploads architecture-specific packages as artifacts

  7. push - Publishes packages to registries

    • Downloads all built packages from previous jobs
    • Pushes multi-platform function package to the configured OCI registry
    • Pushes configuration package to the registry
    • Only runs if XPKG_ACCESS_ID and XPKG_TOKEN secrets are configured
    • Defaults to GitHub Container Registry (ghcr.io)

Configuration:

  • Node.js 24 (LTS)
  • Crossplane CLI (stable channel, current version)
  • Can push to Upbound registry or any OCI-compatible registry

Tag Workflow (tag.yml)

Manual workflow for creating Git tags:

  • Triggered via workflow dispatch only
  • Requires version (e.g., v0.1.0) and message inputs
  • Creates an annotated Git tag using the provided information
  • Useful for marking releases

Usage:

  1. Go to Actions tab in GitHub
  2. Select "Tag" workflow
  3. Click "Run workflow"
  4. Enter version and tag message
  5. Confirm to create the tag

Dependencies

Production Dependencies

  • @crossplane-org/function-sdk-typescript - Crossplane function SDK
  • commander - CLI argument parsing
  • pino - Structured logging
  • kubernetes-models - Type-safe Kubernetes resource models
  • typescript - TypeScript compiler
  • @types/node - Node.js type definitions
  • yaml - YAML parsing for test cases

Dev Dependencies

  • @typescript/native-preview - TypeScript 7 (tsgo) native preview tooling
  • jest - Testing framework
  • ts-jest - TypeScript support for Jest
  • @types/jest - Jest type definitions
  • eslint - Linting
  • typescript-eslint - TypeScript ESLint plugin
  • prettier - Code formatting
  • glob - File pattern matching for test discovery

Notes

  • The SDK is now available as @crossplane-org/function-sdk-typescript on npm
  • mTLS is enabled by default when running in production (disable with --insecure for local dev)
  • Tests are automatically discovered from YAML files in the test-cases/ directory
  • Build scripts in scripts/ handle Docker and xpkg packaging

Troubleshooting

TypeScript Compilation Errors

If you encounter TypeScript errors:

  1. Run npm install to ensure dependencies are properly installed
  2. Try clearing the build directory: npm run clean
  3. Check that TypeScript version is 5+ or use tsgo (TypeScript 7)

Test Failures

If tests fail:

  1. Verify test case YAML files are properly formatted in test-cases/
  2. Check that expected resources match what your function generates
  3. Run tests with verbose output: NODE_OPTIONS=--experimental-vm-modules jest --verbose

Docker Build Failures

If the Docker build fails:

  1. Ensure all dependencies in package.json are available
  2. Check that the build completes successfully locally first: npm run build
  3. Verify Docker has access to the project directory

License

Apache-2.0

Author

Steven Borrelli steve@borrelli.org

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Crossplane template function for Typescript

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Releases 1

v0.1.0 - Initial Release Latest
Feb 6, 2026

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