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Embedded Functions

This document explains the basics of embedded functions and how they work in control plane projects. Embedded functions provide a lightweight way to customize composition behavior without the complexity of managing separate containerized functions.

An embedded function is a lightweight, self-contained unit of logic that runs inside your control plane as part of a function pipeline. Embedded functions allow you to customize how your compositions behave by injecting defaults, transforming data, validating inputs, generating outputs, or reacting to external signals.

Embedded functions vs traditional Crossplane functions​

While both embedded functions and upstream Crossplane functions serve the same purpose of extending your control plane with custom logic, they differ significantly in how you author, deploy, and manage them.

You design embedded functions to be lightweight and tightly integrated into your control plane project. In contrast, upstream Crossplane functions follow a more traditional Kubernetes model, requiring containerized deployments and additional Kubernetes resources.

Key differences​

Deployment and Management: You bundle embedded functions directly into your control plane project. You don't need to deploy additional Function custom resources or manage sidecar containers. You typically containerize upstream functions as workloads that you must deploy into the cluster and manage separately.

Performance and Overhead: Embedded functions run in-memory as part of the control plane's reconciliation loop. This makes them faster and more efficient, with less runtime overhead compared to containerized upstream functions that operate as external processes.

Portability and Versioning: Because embedded functions live inside your control plane project package, you version them alongside your infrastructure definitions. This ensures that your logic and configuration evolve together, making control planes fully portable across environments. You version upstream functions independently and require separate coordination to ensure compatibility.

Developer Experience: Embedded functions support multiple languages including Go, KCL, Python, and Go-templating, offering greater flexibility for teams with diverse skill sets. You typically author upstream functions in Go and require container build and deployment pipelines, which can be a heavier lift for platform teams.

Use cases​

Use embedded functions when you want:

  • Fast, low-overhead customization for compositions
  • A fully declarative control plane project with all logic embedded and versioned
  • Simpler developer workflows without managing containers
  • Reusable, language-flexible logic that travels with your platform configuration