Create a managed or user-assigned NAT gateway for your Azure Kubernetes Service (AKS) cluster

Article
05/31/2023

While you can route egress traffic through an Azure Load Balancer, there are limitations on the number of outbound flows of traffic you can have. Azure NAT Gateway allows up to 64,512 outbound UDP and TCP traffic flows per IP address with a maximum of 16 IP addresses.

This article shows you how to create an Azure Kubernetes Service (AKS) cluster with a managed NAT gateway and a user-assigned NAT gateway for egress traffic. It also shows you how to disable OutboundNAT on Windows.

Before you begin

Make sure you're using the latest version of Azure CLI.
Make sure you're using Kubernetes version 1.20.x or above.
Managed NAT gateway is incompatible with custom virtual networks.

Create an AKS cluster with a managed NAT gateway

Create an AKS cluster with a new managed NAT gateway using the az aks create command with the --outbound-type managedNATGateway, --nat-gateway-managed-outbound-ip-count, and --nat-gateway-idle-timeout parameters. If you want the NAT gateway to operate out of availability zones, specify the zones using --zones.
```
az aks create \
    --resource-group myResourceGroup \
    --name myNatCluster \
    --node-count 3 \
    --outbound-type managedNATGateway \
    --nat-gateway-managed-outbound-ip-count 2 \
    --nat-gateway-idle-timeout 4
```
Important

If no value for the outbound IP address is specified, the default value is one.

Update the number of outbound IP addresses

Update the outbound IP address or idle timeout using the az aks update command with the --nat-gateway-managed-outbound-ip-count or --nat-gateway-idle-timeout parameter.
```
az aks update \ 
    --resource-group myResourceGroup \
    --name myNatCluster\
    --nat-gateway-managed-outbound-ip-count 5
```

Create an AKS cluster with a user-assigned NAT gateway

This configuration requires bring-your-own networking (via Kubenet or Azure CNI) and that the NAT gateway is preconfigured on the subnet. The following commands create the required resources for this scenario.

Create a resource group using the az group create command.

az group create --name myResourceGroup \
    --location southcentralus

Create a managed identity for network permissions and store the ID to $IDENTITY_ID for later use.

IDENTITY_ID=$(az identity create \
    --resource-group myResourceGroup \
    --name myNatClusterId \
    --location southcentralus \
    --query id \
    --output tsv)

Create a public IP for the NAT gateway using the az network public-ip create command.

az network public-ip create \
    --resource-group myResourceGroup \
    --name myNatGatewayPip \
    --location southcentralus \
    --sku standard

Create the NAT gateway using the az network nat gateway create command.

az network nat gateway create \
    --resource-group myResourceGroup \
    --name myNatGateway \
    --location southcentralus \
    --public-ip-addresses myNatGatewayPip

Create a virtual network using the az network vnet create command.

az network vnet create \
    --resource-group myResourceGroup \
    --name myVnet \
    --location southcentralus \
    --address-prefixes 172.16.0.0/20

Create a subnet in the virtual network using the NAT gateway and store the ID to $SUBNET_ID for later use.

SUBNET_ID=$(az network vnet subnet create \
    --resource-group myResourceGroup \
    --vnet-name myVnet \
    --name myNatCluster \
    --address-prefixes 172.16.0.0/22 \
    --nat-gateway myNatGateway \
    --query id \
    --output tsv)

Create an AKS cluster using the subnet with the NAT gateway and the managed identity using the az aks create command.

az aks create \
    --resource-group myResourceGroup \
    --name myNatCluster \
    --location southcentralus \
    --network-plugin azure \
    --vnet-subnet-id $SUBNET_ID \
    --outbound-type userAssignedNATGateway \
    --enable-managed-identity \
    --assign-identity $IDENTITY_ID

Disable OutboundNAT for Windows (preview)

Windows OutboundNAT can cause certain connection and communication issues with your AKS pods. Some of these issues include:

Unhealthy backend status: When you deploy an AKS cluster with Application Gateway Ingress Control (AGIC) and Application Gateway in different VNets, the backend health status becomes "Unhealthy." The outbound connectivity fails because the peered networked IP isn't present in the CNI config of the Windows nodes.
Node port reuse: Windows OutboundNAT uses port to translate your pod IP to your Windows node host IP, which can cause an unstable connection to the external service due to a port exhaustion issue.
Invalid traffic routing to internal service endpoints: When you create a load balancer service with externalTrafficPolicy set to Local, kube-proxy on Windows doesn't create the proper rules in the IPTables to route traffic to the internal service endpoints.

Windows enables OutboundNAT by default. You can now manually disable OutboundNAT when creating new Windows agent pools.

Note

OutboundNAT can only be disabled on Windows Server 2019 node pools.

Prerequisites

You need to use aks-preview and register the feature flag.

Install or update aks-preview using the az extension add or az extension update command.

# Install aks-preview

az extension add --name aks-preview

# Update aks-preview

az extension update --name aks-preview

az feature register --namespace Microsoft.ContainerService --name DisableWindowsOutboundNATPreview

Check the registration status using the az feature list command.

az feature list -o table --query "[?contains(name, 'Microsoft.ContainerService/DisableWindowsOutboundNATPreview')].{Name:name,State:properties.state}"

Refresh the registration of the Microsoft.ContainerService resource provider us
```
az provider register --namespace Microsoft.ContainerService
```

Your clusters must have a managed NAT gateway (which may increase the overall cost).
If you're using Kubernetes version 1.25 or older, you need to update your deployment configuration.
If you need to switch from a load balancer to NAT gateway, you can either add a NAT gateway into the VNet or run az aks upgrade to update the outbound type.

Manually disable OutboundNAT for Windows

Manually disable OutboundNAT for Windows when creating new Windows agent pools using the az aks nodepool add command with the --disable-windows-outbound-nat flag.

Note

You can use an existing AKS cluster, but you may need to update the outbound type and add a node pool to enable --disable-windows-outbound-nat.
```
az aks nodepool add \
    --resource-group myResourceGroup
    --cluster-name myNatCluster
    --name mynodepool
    --node-count 3
    --os-type Windows
    --disable-windows-outbound-nat
```

Next steps

For more information on Azure NAT Gateway, see Azure NAT Gateway.