Composition on Crossplane

Composite Resources

A composite resource, or XR, represents a set of Kubernetes resources as a single Kubernetes object. Crossplane creates composite resources when users access a custom API, defined in the CompositeResourceDefinition.

Tip

Composite resources are a composite of Kubernetes resources.
A Composition defines how to compose the resources together.

A composite resource or XR (this page) is a custom API.

Composite Resource Definitions

Composite resource definitions (XRDs) define the schema for a custom API. Users create composite resources (XRs) using the API schema defined by an XRD.

Note

Read the composite resources page for more information about composite resources.

A composite resource or XR is a custom API.

You use two Crossplane types to create a new custom API:

Compositions

Compositions are a template for creating multiple Kubernetes resources as a single composite resource.

A Composition composes individual resources together into a larger, reusable, solution.

An example Composition may combine a virtual machine, storage resources and networking policies. A Composition template links all these individual resources together.

Here’s an example Composition. When you create an AcmeBucket composite resource (XR) that uses this Composition, Crossplane uses the template to create the Amazon S3 Bucket managed resource.

Composition Revisions

This guide discusses the use of “Composition Revisions” to make and roll back changes to a Crossplane Composition. It assumes familiarity with Crossplane and Compositions.

A Composition configures how Crossplane should reconcile a Composite Resource (XR). Put otherwise, when you create an XR the selected Composition determines what resources Crossplane creates in response. For example, you define a PlatformDB XR, which represents your organisation’s common database configuration of an Azure MySQL Server and some firewall rules. The Composition contains the ‘base’ configuration for the MySQL server and the firewall rules that the PlatformDB configuration extends.

Environment Configs

A Crossplane EnvironmentConfig is a cluster-scoped, strongly typed, ConfigMap-like resource used by Compositions. Compositions can use the environment to store information from individual resources or to apply patches.

Crossplane supports multiple EnvironmentConfigs, each acting as a unique data store.

When Crossplane creates a composite resource, Crossplane merges all the EnvironmentConfigs referenced in the associated Composition and creates a unique in-memory environment for that composite resource.

The composite resource can read and write data to their unique in-memory environment.

Composition on Crossplane

Composite Resources

What are XRs, XRDs and Compositions?

Composite Resource Definitions

What are XRs, XRDs and Compositions?

Compositions

Composition Revisions

Environment Configs