Azure Service Operator

Overview

CAPZ interfaces with Azure to create and manage some types of resources using Azure Service Operator (ASO).

More context around the decision for CAPZ to pivot towards using ASO can be found in the proposal.

Primary changes

For most users, the introduction of ASO is expected to be fully transparent and backwards compatible. Changes that may affect specific use cases are described below.

Installation

Beginning with CAPZ v1.11.0, ASO’s control plane will be installed automatically by clusterctl in the capz-system namespace alongside CAPZ’s control plane components. When ASO is already installed on a cluster, installing ASO again with CAPZ is expected to fail and clusterctl cannot install CAPZ without ASO. The suggested workaround for users facing this issue is to uninstall the existing ASO control plane (but keep the ASO CRDs) and then to install CAPZ.

Bring-your-own (BYO) resource

CAPZ had already allowed users to pre-create some resources like resource groups and virtual networks and reference those resources in CAPZ resources. CAPZ will then use those existing resources without creating new ones and assume the user is responsible for managing them, so will not actively reconcile changes to or delete those resources.

This use case is still supported with ASO installed. The main difference is that an ASO resource will be created for CAPZ’s own bookkeeping, but configured not to be actively reconciled by ASO. When the Cluster API Cluster owning the resource is deleted, the ASO resource will also be deleted from the management cluster but the resource will not be deleted in Azure.

Additionally, BYO resources may include ASO resources managed by the user. CAPZ will not modify or delete such resources. Note that clusterctl move will not move user-managed ASO resources.

Configuration with Environment Variables

These environment variables are passed through to the aso-controller-settings Secret to configure ASO when CAPZ is installed and are consumed by clusterctl init. They may also be modified directly in the Secret after installing ASO with CAPZ:

  • AZURE_AUTHORITY_HOST
  • AZURE_RESOURCE_MANAGER_AUDIENCE
  • AZURE_RESOURCE_MANAGER_ENDPOINT
  • AZURE_SYNC_PERIOD

More details on each can be found in ASO’s documentation.

Using ASO for non-CAPZ resources

CAPZ’s installation of ASO can be used directly to manage Azure resources outside the domain of Cluster API.

Installing more CRDs

For a fresh installation

Before performing a clusterctl init, users can specify additional ASO CRDs to be installed in the management cluster by exporting ADDITIONAL_ASO_CRDS variable. For example, to install all the CRDs of cache.azure.com and MongodbDatabase.documentdb.azure.com:

  • export ADDITIONAL_ASO_CRDS="cache.azure.com/*;documentdb.azure.com/MongodbDatabase"
  • continue with the installation of CAPZ as specified here Cluster API Quick Start.

For an existing CAPZ installation being upgraded to v1.14.0(or beyond)

CAPZ’s installation of ASO configures only the ASO CRDs that are required by CAPZ. To make more resource types available, export ADDITIONAL_ASO_CRDS and then upgrade CAPZ. For example, to install the all CRDs of cache.azure.com and MongodbDatabase.documentdb.azure.com, follow these steps:

  • export ADDITIONAL_ASO_CRDS="cache.azure.com/*;documentdb.azure.com/MongodbDatabase"
  • continue with the upgrade of CAPZ as specified [here](https://cluster-api.sigs.k8s.io/tasks/upgrading-cluster-api-versions.html?highlight=upgrade#when-to-upgrade]

You will see that the --crd-pattern in Azure Service Operator’s Deployment (in the capz-system namespace) looks like below:

.
- --crd-names=cache.azure.com/*;documentdb.azure.com/MongodbDatabase
.

More details about how ASO manages CRDs can be found here.

Note: To install the resource for the newly installed CRDs, make sure that the ASO operator has the authentication to install the resources. Refer authentication in ASO for more details. An example configuration file and demo for Azure Cache for Redis can be found here.

Experimental ASO API

New in CAPZ v1.15.0 is a new flavor of APIs that addresses the following limitations of the existing CAPZ APIs for advanced use cases:

  • A limited set of Azure resource types can be represented.
  • A limited set of Azure resource topologies can be expressed. e.g. Only a single Virtual Network resource can be reconciled for each CAPZ-managed AKS cluster.
  • For each Azure resource type supported by CAPZ, CAPZ generally only uses a single Azure API version to define resources of that type.
  • For each Azure API version known by CAPZ, only a subset of fields defined in that version by the Azure API spec are exposed by the CAPZ API.

This new experimental API defines new AzureASOManagedCluster, AzureASOManagedControlPlane, and AzureASOManagedMachinePool resources. An AzureASOManagedCluster might look like this:

apiVersion: infrastructure.cluster.x-k8s.io/v1alpha1
kind: AzureASOManagedCluster
metadata:
  name: my-cluster
  namespace: default
spec:
  resources:
  - apiVersion: resources.azure.com/v1api20200601
    kind: ResourceGroup
    metadata:
      name: my-resource-group
    spec:
      location: eastus

See here for a full AKS example using all the new resources.

The main element of the new API is spec.resources in each new resource, which defines arbitrary, literal ASO resources inline to be managed by CAPZ. These inline ASO resource definitions take the place of almost all other configuration currently defined by CAPZ. e.g. Instead of a CAPZ-specific spec.location field on the existing AzureManagedControlPlane, the same value would be expected to be set on an ASO ManagedCluster resource defined in an AzureASOManagedControlPlane’s spec.resources. This pattern allows users to define, in full, any ASO-supported version of a resource type in any of these new CAPZ resources.

The obvious tradeoff with this new style of API is that CAPZ resource definitions can become more verbose for basic use cases. To address this, CAPZ still offers flavor templates that use this API with all of the boilerplate predefined to serve as a starting point for customization.

The overall theme of this API is to leverage ASO as much as possible for representing Azure resources in the Kubernetes API, thereby making CAPZ the thinnest possible translation layer between ASO and Cluster API.

This experiment will help inform CAPZ whether this pattern may be a candidate for a potential v2 API. This functionality is available behind the ASOAPI feature flag (set by the EXP_ASO_API environment variable). Please try it out and offer any feedback!