Use an internal load balancer with Azure Kubernetes Service (AKS)

You can create and use an internal load balancer to restrict access to your applications in Azure Kubernetes Service (AKS). An internal load balancer doesn't have a public IP and makes a Kubernetes service accessible only to applications that can reach the private IP. These applications can be within the same VNET or in another VNET through VNET peering. This article shows you how to create and use an internal load balancer with AKS.

Before you begin

• This article assumes that you have an existing AKS cluster. If you need an AKS cluster, you can create one using Azure CLI, Azure PowerShell, or the Azure portal.
• You need the Azure CLI version 2.0.59 or later. Run az --version to find the version. If you need to install or upgrade, see Install Azure CLI.
• If you want to use an existing subnet or resource group, the AKS cluster identity needs permission to manage network resources. For information, see Use kubenet networking with your own IP address ranges in AKS or Configure Azure CNI networking in AKS. If you're configuring your load balancer to use an IP address in a different subnet, ensure the AKS cluster identity also has read access to that subnet.
  • For more information on permissions, see Delegate AKS access to other Azure resources.

Create an internal load balancer

1. Create a service manifest named internal-lb.yaml with the service type LoadBalancer and the azure-load-balancer-internal annotation.

   apiVersion: v1
   kind: Service
   metadata:
     name: internal-app
     annotations:
       service.beta.kubernetes.io/azure-load-balancer-internal: "true"
   spec:
     type: LoadBalancer
     ports:
     - port: 80
     selector:
       app: internal-app
   

2. Deploy the internal load balancer using the kubectl apply command. This command creates an Azure load balancer in the node resource group connected to the same virtual network as your AKS cluster.

   kubectl apply -f internal-lb.yaml
   

3. View the service details using the kubectl get service command.

   kubectl get service internal-app
   

   The IP address of the internal load balancer is shown in the EXTERNAL-IP column, as shown in the following example output. In this context, External refers to the external interface of the load balancer. It doesn't mean that it receives a public, external IP address. This IP address is dynamically assigned from the same subnet as the AKS cluster.

   NAME           TYPE           CLUSTER-IP    EXTERNAL-IP   PORT(S)        AGE
   internal-app   LoadBalancer   10.0.248.59   10.240.0.7    80:30555/TCP   2m
   

Specify an IP address

When you specify an IP address for the load balancer, the specified IP address must reside in the same virtual network as the AKS cluster, but it can't already be assigned to another resource in the virtual network. For example, you shouldn't use an IP address in the range designated for the Kubernetes subnet within the AKS cluster. Using an IP address that's already assigned to another resource in the same virtual network can cause issues with the load balancer.

You can use the az network vnet subnet list Azure CLI command or the Get-AzVirtualNetworkSubnetConfig PowerShell cmdlet to get the subnets in your virtual network.

For more information on subnets, see Add a node pool with a unique subnet.

If you want to use a specific IP address with the load balancer, you have two options: set service annotations or add the LoadBalancerIP property to the load balancer YAML manifest.

2. View the service details using the kubectl get service command.

   kubectl get service internal-app
   

   The IP address in the EXTERNAL-IP column should reflect your specified IP address, as shown in the following example output:

   NAME           TYPE           CLUSTER-IP     EXTERNAL-IP   PORT(S)        AGE
   internal-app   LoadBalancer   10.0.184.168   10.240.0.25   80:30225/TCP   4m
   

For more information on configuring your load balancer in a different subnet, see Specify a different subnet

Connect Azure Private Link service to internal load balancer

Before you begin

• You need Kubernetes version 1.22.x or later.
• You need an existing resource group with a VNet and subnet. This resource group is where you create the private endpoint. If you don't have these resources, see Create a virtual network and subnet.

Create a Private Link service connection

1. Create a service manifest named internal-lb-pls.yaml with the service type LoadBalancer and the azure-load-balancer-internal and azure-pls-create annotations. For more options, refer to the Azure Private Link Service Integration design document.

   apiVersion: v1
   kind: Service
   metadata:
     name: internal-app
     annotations:
       service.beta.kubernetes.io/azure-load-balancer-internal: "true"
       service.beta.kubernetes.io/azure-pls-create: "true"
   spec:
     type: LoadBalancer
     ports:
     - port: 80
     selector:
       app: internal-app
   

2. Deploy the internal load balancer using the kubectl apply command. This command creates an Azure load balancer in the node resource group connected to the same virtual network as your AKS cluster. It also creates a Private Link Service object that connects to the frontend IP configuration of the load balancer associated with the Kubernetes service.

   kubectl apply -f internal-lb-pls.yaml
   

3. View the service details using the kubectl get service command.

   kubectl get service internal-app
   

   The IP address of the internal load balancer is shown in the EXTERNAL-IP column, as shown in the following example output. In this context, External refers to the external interface of the load balancer. It doesn't mean that it receives a public, external IP address.

   NAME           TYPE           CLUSTER-IP    EXTERNAL-IP   PORT(S)        AGE
   internal-app   LoadBalancer   10.125.17.53  10.125.0.66   80:30430/TCP   64m
   

4. View the details of the Private Link Service object using the az network private-link-service list command.

   # Create a variable for the node resource group
   
   AKS_MC_RG=$(az aks show -g myResourceGroup --name myAKSCluster --query nodeResourceGroup -o tsv)
   
   # View the details of the Private Link Service object
   
   az network private-link-service list -g $AKS_MC_RG --query "[].{Name:name,Alias:alias}" -o table
   

   Your output should look similar to the following example output:

   Name      Alias
   --------  -------------------------------------------------------------------------
   pls-xyz   pls-xyz.abc123-defg-4hij-56kl-789mnop.eastus2.azure.privatelinkservice
   

Create a Private Endpoint to the Private Link service

A Private Endpoint allows you to privately connect to your Kubernetes service object via the Private Link Service you created.

• Create the private endpoint using the az network private-endpoint create command.

  # Create a variable for the private link service
  
  AKS_PLS_ID=$(az network private-link-service list -g $AKS_MC_RG --query "[].id" -o tsv)
  
  # Create the private endpoint
  
  $ az network private-endpoint create \
      -g myOtherResourceGroup \
      --name myAKSServicePE \
      --vnet-name myOtherVNET \
      --subnet pe-subnet \
      --private-connection-resource-id $AKS_PLS_ID \
      --connection-name connectToMyK8sService
  

PLS Customizations via Annotations

The following are annotations that can be used to customize the PLS resource.

Annotation	Value	Description	Required	Default
service.beta.kubernetes.io/azure-pls-create	"true"	Boolean indicating whether a PLS needs to be created.	Required
service.beta.kubernetes.io/azure-pls-name	<PLS name>	String specifying the name of the PLS resource to be created.	Optional	"pls-<LB frontend config name>"
service.beta.kubernetes.io/azure-pls-resource-group	Resource Group name	String specifying the name of the Resource Group where the PLS resource will be created	Optional	MC_ resource
service.beta.kubernetes.io/azure-pls-ip-configuration-subnet	<Subnet name>	String indicating the subnet to which the PLS will be deployed. This subnet must exist in the same VNET as the backend pool. PLS NAT IPs are allocated within this subnet.	Optional	If service.beta.kubernetes.io/azure-load-balancer-internal-subnet, this ILB subnet is used. Otherwise, the default subnet from config file is used.
service.beta.kubernetes.io/azure-pls-ip-configuration-ip-address-count	[1-8]	Total number of private NAT IPs to allocate.	Optional	1
service.beta.kubernetes.io/azure-pls-ip-configuration-ip-address	"10.0.0.7 ... 10.0.0.10"	A space separated list of static IPv4 IPs to be allocated. (IPv6 is not supported right now.) Total number of IPs should not be greater than the ip count specified in service.beta.kubernetes.io/azure-pls-ip-configuration-ip-address-count. If there are fewer IPs specified, the rest are dynamically allocated. The first IP in the list is set as Primary.	Optional	All IPs are dynamically allocated.
service.beta.kubernetes.io/azure-pls-fqdns	"fqdn1 fqdn2"	A space separated list of fqdns associated with the PLS.	Optional	[]
service.beta.kubernetes.io/azure-pls-proxy-protocol	"true" or "false"	Boolean indicating whether the TCP PROXY protocol should be enabled on the PLS to pass through connection information, including the link ID and source IP address. Note that the backend service MUST support the PROXY protocol or the connections will fail.	Optional	false
service.beta.kubernetes.io/azure-pls-visibility	"sub1 sub2 sub3 … subN" or "*"	A space separated list of Azure subscription ids for which the private link service is visible. Use "*" to expose the PLS to all subs (Least restrictive).	Optional	Empty list [] indicating role-based access control only: This private link service will only be available to individuals with role-based access control permissions within your directory. (Most restrictive)
service.beta.kubernetes.io/azure-pls-auto-approval	"sub1 sub2 sub3 … subN"	A space separated list of Azure subscription ids. This allows PE connection requests from the subscriptions listed to the PLS to be automatically approved. This only works when visibility is set to "*".	Optional	[]

Use private networks

When you create your AKS cluster, you can specify advanced networking settings. These settings allow you to deploy the cluster into an existing Azure virtual network and subnets. For example, you can deploy your AKS cluster into a private network connected to your on-premises environment and run services that are only accessible internally.

For more information, see configure your own virtual network subnets with Kubenet or with Azure CNI.

You don't need to make any changes to the previous steps to deploy an internal load balancer that uses a private network in an AKS cluster. The load balancer is created in the same resource group as your AKS cluster, but it's instead connected to your private virtual network and subnet, as shown in the following example:

$ kubectl get service internal-app

NAME           TYPE           CLUSTER-IP    EXTERNAL-IP   PORT(S)        AGE
internal-app   LoadBalancer   10.1.15.188   10.0.0.35     80:31669/TCP   1m

Specify a different subnet

• Add the azure-load-balancer-internal-subnet annotation to your service to specify a subnet for your load balancer. The subnet specified must be in the same virtual network as your AKS cluster. When deployed, the load balancer EXTERNAL-IP address is part of the specified subnet.

  apiVersion: v1
  kind: Service
  metadata:
    name: internal-app
    annotations:
      service.beta.kubernetes.io/azure-load-balancer-internal: "true"
      service.beta.kubernetes.io/azure-load-balancer-internal-subnet: "apps-subnet"
  spec:
    type: LoadBalancer
    ports:
    - port: 80
    selector:
      app: internal-app
  

Delete the load balancer

The load balancer is deleted when all of its services are deleted.

As with any Kubernetes resource, you can directly delete a service, such as kubectl delete service internal-app, which also deletes the underlying Azure load balancer.

Next steps

To learn more about Kubernetes services, see the Kubernetes services documentation.