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0012-clusterctl-provider.md

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12. Clusterctl Config resource

  • Status: proposed
  • Date: 2024-09-03
  • Authors: @Danil-Grigorev
  • Deciders: @alexander-demicev @furkatgofurov7 @salasberryfin @Danil-Grigorev @mjura @yiannistri

Context

The current implementation of clusterctl overrides is managed through ConfigMap deployed by turtles helm chart, which has limitations when it comes to custom providers introduction and maintenance, as it requires an update for the ConfigMap content, followed by rancher/turtles release.

The content of the ConfigMap is not easy to override without introducing issues, and it also makes the cluster configuration drift from the one installed with the turtles helm release.

Decision

The proposed solution involves introducing a new singleton namespaced CustomResource - ClusterctlConfig, which will manage clusterctl overrides in a more flexible and maintainable way. The ClusterctlConfig CRD will provide images override options for airGapped installations and enable users to override or extend the default configuration with new providers specific to their use-case.

This additional customization layer would allow to test new provider integrations early, and will not require immediate changes to turtles repository, which will align it with the current certification process.

apiVersion: turtles-capi.cattle.io/v1alpha1
kind: ClusterctlConfig
metadata:
  name: clusterctl-config # Constant name
  namespace: rancher-turtles-system # Release namaespace
spec:
  images: # https://cluster-api.sigs.k8s.io/clusterctl/configuration#image-overrides
  - name: all
    repository: myorg.io/local-repo
  providers: # https://cluster-api.sigs.k8s.io/clusterctl/configuration#provider-repositories
  - name: "my-infra-provider"
    url: "https://github.com/myorg/myrepo/releases/latest/infrastructure-components.yaml"
    type: "InfrastructureProvider"

The resource will manage the singleton ConfigMap mounted in the turtles Deployment, preserving existing functionality. The default ConfigMap for clusterctl.yaml overrides will be embedded into turtles release, and will serve as a default or a starting point for further modifications or customizations.

Mounted ConfigMap is updated automatically on a change, using kubelet automatic mount updates.

Turtles will not deploy initial configuration of the resource, it will be on third-party integrations or the end user to provide customizations and deploy the resource with overrides. Turtles will consistently maintain the combined state of embedded value and user-provided config with overrides, which will be synced into mounted ConfigMap.

Addition of a provider to the list also allows to pin the latest version for the CAPIProvider, which references this provider name, to a specific value. This action prevents unexpected upgrade beyond compatibility matrix with the current core provider version.

Consequences

  • Turtles clusterctl ConfigMap will be managed by the new custom resource.
  • Users will be allowed to override or extend the default configuration with values or providers specific to use-case, outside of turtles release cycle.