Machine Infrastructure Provider Specification

Overview

A machine infrastructure provider is responsible for managing the lifecycle of provider-specific machine instances. These may be physical or virtual instances, and they represent the infrastructure for Kubernetes nodes.

Data Types

A machine infrastructure provider must define an API type for “infrastructure machine” resources. The type:

  1. Must belong to an API group served by the Kubernetes apiserver
  2. May be implemented as a CustomResourceDefinition, or as part of an aggregated apiserver
  3. Must be namespace-scoped
  4. Must have the standard Kubernetes “type metadata” and “object metadata”
  5. Must have a spec field with the following:
    1. Required fields:
      1. providerID (string): the identifier for the provider’s machine instance
    2. Optional fields:
      1. failureDomain (string): the string identifier of the failure domain the instance is running in for the purposes of backwards compatibility and migrating to the v1alpha3 FailureDomain support (where FailureDomain is specified in Machine.Spec.FailureDomain). This field is meant to be temporary to aid in migration of data that was previously defined on the provider type and providers will be expected to remove the field in the next version that provides breaking API changes, favoring the value defined on Machine.Spec.FailureDomain instead. If supporting conversions from previous types, the provider will need to support a conversion from the provider-specific field that was previously used to the failureDomain field to support the automated migration path.
  6. Must have a status field with the following:
    1. Required fields:
      1. ready (boolean): indicates the provider-specific infrastructure has been provisioned and is ready
    2. Optional fields:
      1. failureReason (string): indicates there is a fatal problem reconciling the provider’s infrastructure; meant to be suitable for programmatic interpretation
      2. failureMessage (string): indicates there is a fatal problem reconciling the provider’s infrastructure; meant to be a more descriptive value than failureReason
      3. addresses (MachineAddress): a list of the host names, external IP addresses, internal IP addresses, external DNS names, and/or internal DNS names for the provider’s machine instance. MachineAddress is defined as: - type (string): one of Hostname, ExternalIP, InternalIP, ExternalDNS, InternalDNS - address (string)

Behavior

A machine infrastructure provider must respond to changes to its “infrastructure machine” resources. This process is typically called reconciliation. The provider must watch for new, updated, and deleted resources and respond accordingly.

The following diagram shows the typical logic for a machine infrastructure provider:

Machine infrastructure provider activity diagram

Normal resource

  1. If the resource does not have a Machine owner, exit the reconciliation
    1. The Cluster API Machine reconciler populates this based on the value in the Machines‘s spec.infrastructureRef field
  2. If the resource has status.failureReason or status.failureMessage set, exit the reconciliation
  3. If the Cluster to which this resource belongs cannot be found, exit the reconciliation
  4. Add the provider-specific finalizer, if needed
  5. If the associated Cluster‘s status.infrastructureReady is false, exit the reconciliation
  6. If the associated Machine‘s spec.bootstrap.dataSecretName is nil, exit the reconciliation
  7. Reconcile provider-specific machine infrastructure
    1. If any errors are encountered:
      1. If they are terminal failures, set status.failureReason and status.failureMessage
      2. Exit the reconciliation
    2. If this is a control plane machine, register the instance with the provider’s control plane load balancer (optional)
  8. Set spec.providerID to the provider-specific identifier for the provider’s machine instance
  9. Set status.ready to true
  10. Set status.addresses to the provider-specific set of instance addresses (optional)
  11. Set spec.failureDomain to the provider-specific failure domain the instance is running in (optional)
  12. Patch the resource to persist changes

Deleted resource

  1. If the resource has a Machine owner
    1. Perform deletion of provider-specific machine infrastructure
    2. If this is a control plane machine, deregister the instance from the provider’s control plane load balancer (optional)
    3. If any errors are encountered, exit the reconciliation
  2. Remove the provider-specific finalizer from the resource
  3. Patch the resource to persist changes

RBAC

Provider controller

A machine infrastructure provider must have RBAC permissions for the types it defines. If you are using kubebuilder to generate new API types, these permissions should be configured for you automatically. For example, the AWS provider has the following configuration for its AWSMachine type:

// +kubebuilder:rbac:groups=infrastructure.cluster.x-k8s.io,resources=awsmachines,verbs=get;list;watch;create;update;patch;delete
// +kubebuilder:rbac:groups=infrastructure.cluster.x-k8s.io,resources=awsmachines/status,verbs=get;update;patch

A machine infrastructure provider may also need RBAC permissions for other types, such as Cluster and Machine. If you need read-only access, you can limit the permissions to get, list, and watch. You can use the following configuration for retrieving Cluster and Machine resources:

// +kubebuilder:rbac:groups=cluster.x-k8s.io,resources=clusters;clusters/status,verbs=get;list;watch
// +kubebuilder:rbac:groups=cluster.x-k8s.io,resources=machines;machines/status,verbs=get;list;watch

Cluster API controllers

The Cluster API controller for Machine resources is configured with full read/write RBAC permissions for all resources in the infrastructure.cluster.x-k8s.io API group. This group represents all machine infrastructure providers for SIG Cluster Lifecycle-sponsored provider subprojects. If you are writing a provider not sponsored by the SIG, you must grant full read/write RBAC permissions for the “infrastructure machine” resource in your API group to the Cluster API manager’s ServiceAccount. ClusterRoles can be granted using the aggregation label cluster.x-k8s.io/aggregate-to-manager: "true". The following is an example ClusterRole for a FooMachine resource:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: capi-foo-machines
  labels:
    cluster.x-k8s.io/aggregate-to-manager: "true"
rules:
- apiGroups:
  - infrastructure.foo.com
  resources:
  - foomachines
  verbs:
  - create
  - delete
  - get
  - list
  - patch
  - update
  - watch

Note, the write permissions allow the Machine controller to set owner references and labels on the “infrastructure machine” resources; they are not used for general mutations of these resources.