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Using the Azure provider extension with Gardener as end-user

The core.gardener.cloud/v1beta1.Shoot resource declares a few fields that are meant to contain provider-specific configuration.

This document describes the configurable options for Azure and provides an example Shoot manifest with minimal configuration that can be used to create an Azure cluster (modulo the landscape-specific information like cloud profile names, secret binding names, etc.).

Azure Provider Credentials

In order for Gardener to create a Kubernetes cluster using Azure infrastructure components, a Shoot has to provide credentials with sufficient permissions to the desired Azure subscription. Every shoot cluster references a SecretBinding or a CredentialsBinding which itself references a Secret, and this Secret contains the provider credentials of the Azure subscription. The SecretBinding/CredentialsBinding is configurable in the Shoot cluster with the field secretBindingName/credentialsBindingName.

Create an Azure Application and Service Principle and obtain its credentials.

Please ensure that the Azure application (spn) has the IAM actions defined here assigned. If no fine-grained permissions/actions required then simply assign the Contributor role.

The example below demonstrates how the secret containing the client credentials of the Azure Application has to look like:

apiVersion: v1
kind: Secret
metadata:
  name: core-azure
  namespace: garden-dev
type: Opaque
data:
  clientID: base64(client-id)
  clientSecret: base64(client-secret)
  subscriptionID: base64(subscription-id)
  tenantID: base64(tenant-id)

⚠️ Depending on your API usage it can be problematic to reuse the same Service Principal for different Shoot clusters due to rate limits. Please consider spreading your Shoots over Service Principals from different Azure subscriptions if you are hitting those limits.

Managed Service Principals

The operators of the Gardener Azure extension can provide managed service principals. This eliminates the need for users to provide an own service principal for a Shoot.

To make use of a managed service principal, the Azure secret of a Shoot cluster must contain only a subscriptionID and a tenantID field, but no clientID and clientSecret. Removing those fields from the secret of an existing Shoot will also let it adopt the managed service principal.

Based on the tenantID field, the Gardener extension will try to assign the managed service principal to the Shoot. If no managed service principal can be assigned then the next operation on the Shoot will fail.

⚠️ The managed service principal need to be assigned to the users Azure subscription with proper permissions before using it.

InfrastructureConfig

The infrastructure configuration mainly describes how the network layout looks like in order to create the shoot worker nodes in a later step, thus, prepares everything relevant to create VMs, load balancers, volumes, etc.

An example InfrastructureConfig for the Azure extension looks as follows:

apiVersion: azure.provider.extensions.gardener.cloud/v1alpha1
kind: InfrastructureConfig
networks:
  vnet: # specify either 'name' and 'resourceGroup' or 'cidr'
    # name: my-vnet
    # resourceGroup: my-vnet-resource-group
    cidr: 10.250.0.0/16
    # ddosProtectionPlanID: /subscriptions/test/resourceGroups/test/providers/Microsoft.Network/ddosProtectionPlans/test-ddos-protection-plan
  workers: 10.250.0.0/19
  # natGateway:
  #   enabled: false
  #   idleConnectionTimeoutMinutes: 4
  #   zone: 1
  #   ipAddresses:
  #   - name: my-public-ip-name
  #     resourceGroup: my-public-ip-resource-group
  #     zone: 1
  # serviceEndpoints:
  # - Microsoft.Test
  # zones:
  # - name: 1
  #   cidr: "10.250.0.0/24
  # - name: 2
  #   cidr: "10.250.0.0/24"
  #   natGateway:
  #     enabled: false
zoned: false
# resourceGroup:
#   name: mygroup
#identity:
#  name: my-identity-name
#  resourceGroup: my-identity-resource-group
#  acrAccess: true

Currently, it’s not yet possible to deploy into existing resource groups. The .resourceGroup.name field will allow specifying the name of an already existing resource group that the shoot cluster and all infrastructure resources will be deployed to.

Via the .zoned boolean you can tell whether you want to use Azure availability zones or not. If you didn’t use zones in the past then an availability set was created and only basic load balancers were used. Now VMSS-FLex (VMO) has become the default also for non-zonal clusters and only standard load balancers are used.

The networks.vnet section describes whether you want to create the shoot cluster in an already existing VNet or whether to create a new one:

• If networks.vnet.name and networks.vnet.resourceGroup are given then you have to specify the VNet name and VNet resource group name of the existing VNet that was created by other means (manually, other tooling, …).
• If networks.vnet.cidr is given then you have to specify the VNet CIDR of a new VNet that will be created during shoot creation. You can freely choose a private CIDR range.
• Either networks.vnet.name and neworks.vnet.resourceGroup or networks.vnet.cidr must be present, but not both at the same time.
• The networks.vnet.ddosProtectionPlanID field can be used to specify the id of a ddos protection plan which should be assigned to the VNet. This will only work for a VNet managed by Gardener. For externally managed VNets the ddos protection plan must be assigned by other means.
• If a vnet name is given and cilium shoot clusters are created without a network overlay within one vnet make sure that the pod CIDR specified in shoot.spec.networking.pods is not overlapping with any other pod CIDR used in that vnet. Overlapping pod CIDRs will lead to disfunctional shoot clusters.
• It’s possible to place multiple shoot cluster into the same vnet

The networks.workers section describes the CIDR for a subnet that is used for all shoot worker nodes, i.e., VMs which later run your applications. The specified CIDR range must be contained in the VNet CIDR specified above, or the VNet CIDR of your already existing VNet. You can freely choose this CIDR and it is your responsibility to properly design the network layout to suit your needs.

In the networks.serviceEndpoints[] list you can specify the list of Azure service endpoints which shall be associated with the worker subnet. All available service endpoints and their technical names can be found in the (Azure Service Endpoint documentation](https://docs.microsoft.com/en-us/azure/virtual-network/virtual-network-service-endpoints-overview).

The networks.natGateway section contains configuration for the Azure NatGateway which can be attached to the worker subnet of a Shoot cluster. Here are some key information about the usage of the NatGateway for a Shoot cluster:

• NatGateway usage is optional and can be enabled or disabled via .networks.natGateway.enabled.
• If the NatGateway is not used then the egress connections initiated within the Shoot cluster will be nated via the LoadBalancer of the clusters (default Azure behaviour, see here).
• NatGateway is only available for zonal clusters .zoned=true.
• The NatGateway is currently not zone redundantly deployed. That mean the NatGateway of a Shoot cluster will always be in just one zone. This zone can be optionally selected via .networks.natGateway.zone.
• Caution: Modifying the .networks.natGateway.zone setting requires a recreation of the NatGateway and the managed public ip (automatically used if no own public ip is specified, see below). That mean you will most likely get a different public ip for egress connections.
• It is possible to bring own zonal public ip(s) via networks.natGateway.ipAddresses. Those public ip(s) need to be in the same zone as the NatGateway (see networks.natGateway.zone) and be of SKU standard. For each public ip the name, the resourceGroup and the zone need to be specified.
• The field networks.natGateway.idleConnectionTimeoutMinutes allows the configuration of NAT Gateway’s idle connection timeout property. The idle timeout value can be adjusted from 4 minutes, up to 120 minutes. Omitting this property will set the idle timeout to its default value according to NAT Gateway’s documentation.

In the identity section you can specify an Azure user-assigned managed identity which should be attached to all cluster worker machines. With identity.name you can specify the name of the identity and with identity.resourceGroup you can specify the resource group which contains the identity resource on Azure. The identity need to be created by the user upfront (manually, other tooling, …). Gardener/Azure Extension will only use the referenced one and won’t create an identity. Furthermore the identity have to be in the same subscription as the Shoot cluster. Via the identity.acrAccess you can configure the worker machines to use the passed identity for pulling from an Azure Container Registry (ACR). Caution: Adding, exchanging or removing the identity will require a rolling update of all worker machines in the Shoot cluster.

Apart from the VNet and the worker subnet the Azure extension will also create a dedicated resource group, route tables, security groups, and an availability set (if not using zoned clusters).

InfrastructureConfig with dedicated subnets per zone

Another deployment option for zonal clusters only, is to create and configure a separate subnet per availability zone. This network layout is recommended to users that require fine-grained control over their network setup. One prevalent usecase is to create a zone-redundant NAT Gateway deployment by taking advantage of the ability to deploy separate NAT Gateways for each subnet.

To use this configuration the following requirements must be met:

• the zoned field must be set to true.
• the networks.vnet section must not be empty and must contain a valid configuration. For existing clusters that were not using the networks.vnet section, it is enough if networks.vnet.cidr field is set to the current networks.worker value.

For each of the target zones a subnet CIDR range must be specified. The specified CIDR range must be contained in the VNet CIDR specified above, or the VNet CIDR of your already existing VNet. In addition, the CIDR ranges must not overlap with the ranges of the other subnets.

ServiceEndpoints and NatGateways can be configured per subnet. Respectively, when networks.zones is specified, the fields networks.workers, networks.serviceEndpoints and networks.natGateway cannot be set. All the configuration for the subnets must be done inside the respective zone’s configuration.

Example:

apiVersion: azure.provider.extensions.gardener.cloud/v1alpha1
kind: InfrastructureConfig
networks:
  zoned: true
  vnet: # specify either 'name' and 'resourceGroup' or 'cidr'
    cidr: 10.250.0.0/16
  zones:
  - name: 1
    cidr: "10.250.0.0/24"
  - name: 2
    cidr: "10.250.0.0/24"
    natGateway:
      enabled: false

Migrating to zonal shoots with dedicated subnets per zone

For existing zonal clusters it is possible to migrate to a network layout with dedicated subnets per zone. The migration works by creating additional network resources as specified in the configuration and progressively roll part of your existing nodes to use the new resources. To achieve the controlled rollout of your nodes, parts of the existing infrastructure must be preserved which is why the following constraint is imposed:

One of your specified zones must have the exact same CIDR range as the current network.workers field. Here is an example of such migration:

infrastructureConfig:
  apiVersion: azure.provider.extensions.gardener.cloud/v1alpha1
  kind: InfrastructureConfig
  networks:
    vnet:
      cidr: 10.250.0.0/16
    workers: 10.250.0.0/19
  zoned: true

to

infrastructureConfig:
  apiVersion: azure.provider.extensions.gardener.cloud/v1alpha1
  kind: InfrastructureConfig
  networks:
    vnet:
      cidr: 10.250.0.0/16
    zones:
      - name: 3
        cidr: 10.250.0.0/19 # note the preservation of the 'workers' CIDR
# optionally add other zones
    # - name: 2
    #   cidr: 10.250.32.0/19
    #   natGateway:
    #     enabled: true
  zoned: true

Another more advanced example with user-provided public IP addresses for the NAT Gateway and how it can be migrated:

infrastructureConfig:
  apiVersion: azure.provider.extensions.gardener.cloud/v1alpha1
  kind: InfrastructureConfig
  networks:
    vnet:
      cidr: 10.250.0.0/16
    workers: 10.250.0.0/19
    natGateway:
      enabled: true
      zone: 1
      ipAddresses:
        - name: pip1
          resourceGroup: group
          zone: 1
        - name: pip2
          resourceGroup: group
          zone: 1
  zoned: true

to

infrastructureConfig:
  apiVersion: azure.provider.extensions.gardener.cloud/v1alpha1
  kind: InfrastructureConfig
  zoned: true
  networks:
    vnet:
      cidr: 10.250.0.0/16
    zones:
      - name: 1
        cidr: 10.250.0.0/19 # note the preservation of the 'workers' CIDR
        natGateway:
          enabled: true
          ipAddresses:
            - name: pip1
              resourceGroup: group
              zone: 1
            - name: pip2
              resourceGroup: group
              zone: 1
# optionally add other zones
#     - name: 2
#       cidr: 10.250.32.0/19
#       natGateway:
#         enabled: true
#         ipAddresses:
#           - name: pip3
#             resourceGroup: group

You can apply such change to your shoot by issuing a kubectl patch command to replace your current .spec.provider.infrastructureConfig section:

$ cat new-infra.json

[
  {
    "op": "replace",
    "path": "/spec/provider/infrastructureConfig",
    "value": {
      "apiVersion": "azure.provider.extensions.gardener.cloud/v1alpha1",
      "kind": "InfrastructureConfig",
      "networks": {
        "vnet": {
          "cidr": "<your-vnet-cidr>"
        },
        "zones": [
          {
            "name": 1,
            "cidr": "10.250.0.0/24",
            "natGateway": {
              "enabled": true
            }
          },
          {
            "name": 1,
            "cidr": "10.250.1.0/24",
            "natGateway": {
              "enabled": true
            }
          },
        ]
      },
      "zoned": true
    }
  }
]

kubectl patch --type="json" --patch-file new-infra.json shoot <my-shoot>

⚠️ The migration to shoots with dedicated subnets per zone is a one-way process. Reverting the shoot to the previous configuration is not supported.

⚠️ During the migration a subset of the nodes will be rolled to the new subnets.

ControlPlaneConfig

The control plane configuration mainly contains values for the Azure-specific control plane components. Today, the only component deployed by the Azure extension is the cloud-controller-manager.

An example ControlPlaneConfig for the Azure extension looks as follows:

apiVersion: azure.provider.extensions.gardener.cloud/v1alpha1
kind: ControlPlaneConfig
cloudControllerManager:
# featureGates:
#   SomeKubernetesFeature: true

The cloudControllerManager.featureGates contains a map of explicitly enabled or disabled feature gates. For production usage it’s not recommend to use this field at all as you can enable alpha features or disable beta/stable features, potentially impacting the cluster stability. If you don’t want to configure anything for the cloudControllerManager simply omit the key in the YAML specification.

storage contains options for storage-related control plane component. storage.managedDefaultStorageClass is enabled by default and will deploy a storageClass and mark it as a default (via the storageclass.kubernetes.io/is-default-class annotation) storage.managedDefaultVolumeSnapshotClass is enabled by default and will deploy a volumeSnapshotClass and mark it as a default (via the snapshot.storage.kubernetes.io/is-default-classs annotation) In case you want to manage your own default storageClass or volumeSnapshotClass you need to disable the respective options above, otherwise reconciliation of the controlplane may fail.

WorkerConfig

The Azure extension supports encryption for volumes plus support for additional data volumes per machine. Please note that you cannot specify the encrypted flag for Azure disks as they are encrypted by default/out-of-the-box. For each data volume, you have to specify a name. The following YAML is a snippet of a Shoot resource:

spec:
  provider:
    workers:
    - name: cpu-worker
      ...
      volume:
        type: Standard_LRS
        size: 20Gi
      dataVolumes:
      - name: kubelet-dir
        type: Standard_LRS
        size: 25Gi

Additionally, it supports for other Azure-specific values and could be configured under .spec.provider.workers[].providerConfig

An example WorkerConfig for the Azure extension looks like:

apiVersion: azure.provider.extensions.gardener.cloud/v1alpha1
kind: WorkerConfig
nodeTemplate: # (to be specified only if the node capacity would be different from cloudprofile info during runtime)
  capacity:
    cpu: 2
    gpu: 1
    memory: 50Gi
diagnosticsProfile:
  enabled: true
  # storageURI: https://<storage-account-name>.blob.core.windows.net/
dataVolumes:
  - name: test-image
    imageRef:
      communityGalleryImageID: /CommunityGalleries/gardenlinux-13e998fe-534d-4b0a-8a27-f16a73aef620/Images/gardenlinux/Versions/1443.10.0
      # sharedGalleryImageID: /SharedGalleries/82fc46df-cc38-4306-9880-504e872cee18-VSMP_MEMORYONE_GALLERY/Images/vSMP_MemoryONE/Versions/1062800168.0.0
      # id: /Subscriptions/2ebd38b6-270b-48a2-8e0b-2077106dc615/Providers/Microsoft.Compute/Locations/westeurope/Publishers/sap/ArtifactTypes/VMImage/Offers/gardenlinux/Skus/greatest/Versions/1443.10.0
      # urn: sap:gardenlinux:greatest:1443.10.0

The .nodeTemplate is used to specify resource information of the machine during runtime. This then helps in Scale-from-Zero. Some points to note for this field:

• Currently only cpu, gpu and memory are configurable.
• a change in the value lead to a rolling update of the machine in the worker pool
• all the resources needs to be specified

The .diagnosticsProfile is used to enable machine boot diagnostics (disabled per default). A storage account is used for storing vm’s boot console output and screenshots. If .diagnosticsProfile.StorageURI is not specified azure managed storage will be used (recommended way).

The .dataVolumes field is used to add provider specific configurations for dataVolumes. .dataVolumes[].name must match with one of the names in workers.dataVolumes[].name. To specify an image source for the dataVolume either use communityGalleryImageID, sharedGalleryImageID, id or urn as imageRef. However, users have to make sure that the image really exists, there’s yet no check in place. If the image does not exist the machine will get stuck in creation.

Example Shoot manifest (non-zoned)

Please find below an example Shoot manifest for a non-zoned cluster:

apiVersion: core.gardener.cloud/v1beta1
kind: Shoot
metadata:
  name: johndoe-azure
  namespace: garden-dev
spec:
  cloudProfile:
    name: azure
  region: westeurope
  secretBindingName: core-azure
  provider:
    type: azure
    infrastructureConfig:
      apiVersion: azure.provider.extensions.gardener.cloud/v1alpha1
      kind: InfrastructureConfig
      networks:
        vnet:
          cidr: 10.250.0.0/16
        workers: 10.250.0.0/19
      zoned: false
    controlPlaneConfig:
      apiVersion: azure.provider.extensions.gardener.cloud/v1alpha1
      kind: ControlPlaneConfig
    workers:
    - name: worker-xoluy
      machine:
        type: Standard_D4_v3
      minimum: 2
      maximum: 2
      volume:
        size: 50Gi
        type: Standard_LRS
#      providerConfig:
#        apiVersion: azure.provider.extensions.gardener.cloud/v1alpha1
#        kind: WorkerConfig
#        nodeTemplate: # (to be specified only if the node capacity would be different from cloudprofile info during runtime)
#          capacity:
#            cpu: 2
#            gpu: 1
#            memory: 50Gi
  networking:
    type: calico
    pods: 100.96.0.0/11
    nodes: 10.250.0.0/16
    services: 100.64.0.0/13
  kubernetes:
    version: 1.28.2
  maintenance:
    autoUpdate:
      kubernetesVersion: true
      machineImageVersion: true
  addons:
    kubernetesDashboard:
      enabled: true
    nginxIngress:
      enabled: true

Example Shoot manifest (zoned)

Please find below an example Shoot manifest for a zoned cluster:

apiVersion: core.gardener.cloud/v1beta1
kind: Shoot
metadata:
  name: johndoe-azure
  namespace: garden-dev
spec:
  cloudProfile:
    name: azure
  region: westeurope
  secretBindingName: core-azure
  provider:
    type: azure
    infrastructureConfig:
      apiVersion: azure.provider.extensions.gardener.cloud/v1alpha1
      kind: InfrastructureConfig
      networks:
        vnet:
          cidr: 10.250.0.0/16
        workers: 10.250.0.0/19
      zoned: true
    controlPlaneConfig:
      apiVersion: azure.provider.extensions.gardener.cloud/v1alpha1
      kind: ControlPlaneConfig
    workers:
    - name: worker-xoluy
      machine:
        type: Standard_D4_v3
      minimum: 2
      maximum: 2
      volume:
        size: 50Gi
        type: Standard_LRS
      zones:
      - "1"
      - "2"
  networking:
    type: calico
    pods: 100.96.0.0/11
    nodes: 10.250.0.0/16
    services: 100.64.0.0/13
  kubernetes:
    version: 1.28.2
  maintenance:
    autoUpdate:
      kubernetesVersion: true
      machineImageVersion: true
  addons:
    kubernetesDashboard:
      enabled: true
    nginxIngress:
      enabled: true

Example Shoot manifest (zoned with NAT Gateways per zone)

Please find below an example Shoot manifest for a zoned cluster using NAT Gateways per zone:

apiVersion: core.gardener.cloud/v1beta1
kind: Shoot
metadata:
  name: johndoe-azure
  namespace: garden-dev
spec:
  cloudProfile:
    name: azure
  region: westeurope
  secretBindingName: core-azure
  provider:
    type: azure
    infrastructureConfig:
      apiVersion: azure.provider.extensions.gardener.cloud/v1alpha1
      kind: InfrastructureConfig
      networks:
        vnet:
          cidr: 10.250.0.0/16
        zones:
        - name: 1
          cidr: 10.250.0.0/24
          serviceEndpoints:
          - Microsoft.Storage
          - Microsoft.Sql
          natGateway:
            enabled: true
            idleConnectionTimeoutMinutes: 4
        - name: 2
          cidr: 10.250.1.0/24
          serviceEndpoints:
          - Microsoft.Storage
          - Microsoft.Sql
          natGateway:
            enabled: true
      zoned: true
    controlPlaneConfig:
      apiVersion: azure.provider.extensions.gardener.cloud/v1alpha1
      kind: ControlPlaneConfig
    workers:
    - name: worker-xoluy
      machine:
        type: Standard_D4_v3
      minimum: 2
      maximum: 2
      volume:
        size: 50Gi
        type: Standard_LRS
      zones:
      - "1"
      - "2"
  networking:
    type: calico
    pods: 100.96.0.0/11
    nodes: 10.250.0.0/16
    services: 100.64.0.0/13
  kubernetes:
    version: 1.28.2
  maintenance:
    autoUpdate:
      kubernetesVersion: true
      machineImageVersion: true
  addons:
    kubernetesDashboard:
      enabled: true
    nginxIngress:
      enabled: true

CSI volume provisioners

Every Azure shoot cluster will be deployed with the Azure Disk CSI driver and the Azure File CSI driver.

Kubernetes Versions per Worker Pool

This extension supports gardener/gardener’s WorkerPoolKubernetesVersion feature gate, i.e., having worker pools with overridden Kubernetes versions since gardener-extension-provider-azure@v1.25.

Shoot CA Certificate and ServiceAccount Signing Key Rotation

This extension supports gardener/gardener’s ShootCARotation and ShootSARotation feature gates since gardener-extension-provider-azure@v1.28.

Miscellaneous

Azure Accelerated Networking

All worker machines of the cluster will be automatically configured to use Azure Accelerated Networking if the prerequisites are fulfilled. The prerequisites are that the cluster must be zoned, and the used machine type and operating system image version are compatible for Accelerated Networking. Availability Set based shoot clusters will not be enabled for accelerated networking even if the machine type and operating system support it, this is necessary because all machines from the availability set must be scheduled on special hardware, more details can be found here. Supported machine types are listed in the CloudProfile in .spec.providerConfig.machineTypes[].acceleratedNetworking and the supported operating system image versions are defined in .spec.providerConfig.machineImages[].versions[].acceleratedNetworking.

Support for other Azure instances

The provider extension can be configured to connect to Azure instances other than the public one by providing additional configuration in the CloudProfile:

spec:
  …
  providerConfig:
    apiVersion: azure.provider.extensions.gardener.cloud/v1alpha1
    kind: CloudProfileConfig
    cloudConfiguration:
      name: AzurePublic # AzurePublic | AzureGovernment | AzureChina
    machineTypes:
      …
    …
  …

If no configuration is specified the extension will default to the public instance. Azure instances other than AzurePublic, AzureGovernment, or AzureChina are not supported at this time.

Support for VolumeAttributesClasses (Beta in k8s 1.31)

To have the CSI-driver configured to support the necessary features for VolumeAttributesClasses on Azure for shoots with a k8s-version greater than 1.31, use the azure.provider.extensions.gardener.cloud/enable-volume-attributes-class annotation on the shoot. Keep in mind to also enable the required feature flags and runtime-config on the common kubernetes controllers (as outlined in the link above) in the shoot-spec.

For more information and examples on how to configure the volume attributes class, see example provided in the the azuredisk-csi-driver repository.

Preview: Shoot clusters with VMSS Flexible Orchestration (VMSS Flex/VMO)

The machines of an Azure cluster can be created while being attached to an Azure Virtual Machine ScaleSet with flexible orchestraion. The Virtual Machine ScaleSet with flexible orchestration feature is currently in preview and not yet general available on Azure. Subscriptions need to join the preview to make use of the feature.

Azure VMSS Flex is the replacement of Azure AvailabilitySet for non-zoned Azure Shoot clusters as VMSS Flex come with less disadvantages like no blocking machine operations or compatibility with Standard SKU loadbalancer etc.

Now, Azure Shoot clusters are using VMSS Flex by default for non-zoned clusters. In the past you used to need to do the following:

• The InfrastructureConfig of the Shoot configuration need to contain .zoned=false
• Shoot resource need to have the following annotation assigned: alpha.azure.provider.extensions.gardener.cloud/vmo=true

Some key facts about VMSS Flex based clusters:

• Unlike regular non-zonal Azure Shoot clusters, which have a primary AvailabilitySet which is shared between all machines in all worker pools of a Shoot cluster, a VMSS Flex based cluster has an own VMSS for each workerpool
• In case the configuration of the VMSS will change (e.g. amount of fault domains in a region change; configured in the CloudProfile) all machines of the worker pool need to be rolled
• It is not possible to migrate an existing primary AvailabilitySet based Shoot cluster to VMSS Flex based Shoot cluster and vice versa
• VMSS Flex based clusters are using Standard SKU LoadBalancers instead of Basic SKU LoadBalancers for AvailabilitySet based Shoot clusters