VM Identity

This document describes the available identities that be configured on the Azure host. For example, this is what grants permissions to the Azure Cloud Provider to provision LB services in Azure on the control plane nodes.

Flavors of Identities in Azure

All identities used in Azure are owned by Azure Active Directory (AAD). An identity, or principal, in AAD will provide the basis for each of the flavors of identities we will describe.

Managed Identities

Managed identity is a feature of Azure Active Directory (AAD) and Azure Resource Manager (ARM), which assigns ARM Role Base Access Control (RBAC) rights to AAD identities for use in Azure resources, like Virtual Machines. Each of the Azure services that support managed identities for Azure resources are subject to their own timeline. Make sure you review the availability status of managed identities for your resource and known issues before you begin.

Managed identity is used to create nodes which have an AAD identity provisioned onto the node by Azure Resource Manager (the Azure control plane) rather than providing credentials in the azure.json file. Managed identities are the preferred way to provide RBAC rights for a given resource in Azure as the lifespan of the identity is linked to the lifespan of the resource.

User-assigned managed identity (recommended)

A standalone Azure resource that is created by the user outside of the scope of this provider. The identity can be assigned to one or more Azure Machines. The lifecycle of a user-assigned identity is managed separately from the lifecycle of the Azure Machines to which it’s assigned.

This lifecycle allows you to separate your resource creation and identity administration responsibilities. User-assigned identities and their role assignments can be configured in advance of the resources that require them. Users who create the resources only require the access to assign a user-assigned identity, without the need to create new identities or role assignments.

Full details on how to create and manage user assigned identities using Azure CLI can be found in the Azure docs.

System-assigned managed identity

A system-assigned identity is a managed identity which is tied to the lifespan of a resource in Azure. The identity is created by Azure in AAD for the resource it is applied upon and reaped when the resource is deleted. Unlike a service principal, a system assigned identity is available on the local resource through a local port service via the instance metadata service.

⚠️ When a Node is created with a System Assigned Identity, A role of Subscription contributor is added to this generated Identity

How to use managed identity

User-assigned

  • In Machines
apiVersion: infrastructure.cluster.x-k8s.io/v1beta1
kind: AzureMachineTemplate
metadata:
  name: ${CLUSTER_NAME}-md-0
  namespace: default
spec:
  template:
    spec:
      identity: UserAssigned
      userAssignedIdentities:
      - providerID: ${USER_ASSIGNED_IDENTITY_PROVIDER_ID}
      ...

The CAPZ controller will look for UserAssigned value in identity field under AzureMachineTemplate, and assign the user identities listed in userAssignedIdentities to the virtual machine.

  • In Machine Pool
apiVersion: infrastructure.cluster.x-k8s.io/v1beta1
kind: AzureMachinePool
metadata:
  name: ${CLUSTER_NAME}-mp-0
  namespace: default
spec:
  identity: UserAssigned
  userAssignedIdentities:
  - providerID: ${USER_ASSIGNED_IDENTITY_PROVIDER_ID}
  ...

The CAPZ controller will look for UserAssigned value in identity field under AzureMachinePool, and assign the user identities listed in userAssignedIdentities to the virtual machine scale set.

Alternatively, you can use the user-assigned-identity, and machinepool-user-assigned-identity flavors by setting the {flavor} in clusterctl generate cluster --flavor {flavor} to use user-assigned managed identity in machine deployment, and machine pool respectively.

System-assigned

  • In Machines
apiVersion: infrastructure.cluster.x-k8s.io/v1beta1
kind: AzureMachineTemplate
metadata:
  name: ${CLUSTER_NAME}-md-0
  namespace: default
spec:
  template:
    spec:
      identity: SystemAssigned
      ...

The CAPZ controller will look for SystemAssigned value in identity field under AzureMachineTemplate, and enable system-assigned managed identity in the virtual machine.

  • In Machine Pool
apiVersion: infrastructure.cluster.x-k8s.io/v1beta1
kind: AzureMachinePool
metadata:
  name: ${CLUSTER_NAME}-mp-0
  namespace: default
spec:
  identity: SystemAssigned
  ...

The CAPZ controller will look for SystemAssigned value in identity field under AzureMachinePool, and enable system-assigned managed identity in the virtual machine scale set.

Alternatively, you can also use the system-assigned-identity, and machinepool-system-assigned-identity flavors by setting the {flavor} in clusterctl generate cluster --flavor {flavor} to use system-assigned managed identity in machine deployment, and machine pool respectively.

Service Principal (not recommended)

A service principal is an identity in AAD which is described by a tenant ID and client (or “app”) ID. It can have one or more associated secrets or certificates. The set of these values will enable the holder to exchange the values for a JWT token to communicate with Azure. The user generally creates a service principal, saves the credentials, and then uses the credentials in applications. To read more about Service Principals and AD Applications see “Application and service principal objects in Azure Active Directory”.

To use a client id/secret for authentication for Cloud Provider, simply leave the identity empty, or set it to None. The autogenerated cloud provider config secret will contain the client id and secret used in your AzureClusterIdentity for AzureCluster creation as aadClientID and aadClientSecret.

To use a certificate/password for authentication, you will need to write the certificate file on the VM (for example using the files option if using CABPK/cloud-init) and mount it to the cloud-controller-manager, then refer to it as aadClientCertPath, along with aadClientCertPassword, in your cloud provider config. Please consider using a user-assigned identity instead before going down that route as they are more secure and flexible, as described above.

Creating a Service Principal

  • With the Azure CLI

    • Subscription level Scope

      az login
      az account set --subscription="${AZURE_SUBSCRIPTION_ID}"
      az ad sp create-for-rbac --role="Contributor" --scopes="/subscriptions/${AZURE_SUBSCRIPTION_ID}"
      
    • Resource group level scope

      az login
      az account set --subscription="${AZURE_SUBSCRIPTION_ID}"
      az ad sp create-for-rbac --role="Contributor" --scopes="/subscriptions/${AZURE_SUBSCRIPTION_ID}/resourceGroups/${AZURE_RESOURCE_GROUP}"
      

    This will output your appId, password, name, and tenant. The name or appId is used for the AZURE_CLIENT_ID and the password is used for AZURE_CLIENT_SECRET.

    Confirm your service principal by opening a new shell and run the following commands substituting in name, password, and tenant:

    az login --service-principal -u NAME -p PASSWORD --tenant TENANT
    az vm list-sizes --location eastus