Crossplane

Contents

https://www.crossplane.io

Features

provider feature: what everyone talks about
compositions: an extra feature

Provider feature

The objective : define the instance of a CRD inside your custer, and crossplane will take care to create the infrastructure ! For instance, define an s3 bucket, crossplane will create it for you, and recreate it if it gets deleted !

apiVersion: s3.aws.upbound.io/v1beta1
kind: Bucket
metadata:
  generateName: crossplane-bucket-
  labels:
    docs.crossplane.io/example: provider-aws
spec:
  forProvider:
    region: us-east-2
  providerConfigRef:
    name: default

With AWS provider, 900 CRD are defined !
Providers are avilable for AWS, Azure, GCP... and many more

→ In some way, comparable to terraform, with control loops (continuous monitoring).

Compositions

A way to create new CRD, that are going to create several resources when instanciated.
→ In some way, comparable to Helm.

Build Abstractions on APIs
Crossplane Composition maps "higher level" APIs to one or more implementations.
Example: Database API that is implemented by

PostgreSQL Helm Chart
GCP CloudSQL
AWS RDS

Configurations: package and Distribute APIs

Crossplane Configuration packages bundle "higher level" APIs and declare their dependencies.
Crossplane automatically resolves dependencies when a package is installed.
Use Configuration packages as the foundation for future APIs.

Common pattern

ArgoCD or Flux + Crossplane

ArgoCD or Flux create ressources inside the cluster (both workload and CRD)
Crossplane creates the infrastructure based on the CRD

In that situation

For ArgoCD or Flux
- the desired state is GIT
- the actual state is the cluster
For Crossplane
- the desired state is the cluster (CRD)
- the actual state is AWS (for instance)