Load balancer overview

azure-local/multi-rack/multi-rack-load-balancer-overview.md

@@ -0,0 +1,68 @@
+---
+title: About Load Balancers in Multi-Rack Deployments of Azure Local (Preview)
+description: Learn about the types of load balancers you can use in multi-rack deployments of Azure Local (Preview).
+ms.topic: conceptual
+ms.date: 11/20/2025
+author: alkohli
+ms.author: alkohli
+---
+
+# About load balancers in multi-rack deployments of Azure Local (Preview)
+
+[!INCLUDE [multi-rack-applies-to-preview](../includes/multi-rack-applies-to-preview.md)]
+
+This article describes the different types of load balancers you can use in multi-rack deployments of Azure Local.
+
+[!INCLUDE [hci-preview](../includes/hci-preview.md)]
+
+## About load balancers
+
+A load balancer is a fully managed service that distributes incoming traffic across backend virtual machines (VMs). It operates at Layer 4 of the OSI model and distributes inbound flows that arrive at the load balancer’s frontend to backend pool instances according to configured load-balancing rules and health probes.
+
+Multi-rack deployments of Azure Local supports three types of load balancers:
+
+- **Public load balancer on virtual networks.** Provides inbound connectivity from external networks (internet or enterprise WAN) to VMs (NICs). It distributes traffic flows directed to a public frontend IP across a backend pool of VMs in the virtual network.
+
+- **Internal load balancer on virtual networks.** Balances traffic within a virtual network. Use an internal load balancer to provide inbound connectivity to your VMs in private network connectivity scenarios. The internal load balancer uses a private frontend IP.
+
+- **Load balancer on logical networks.** Balances traffic across a backend pool of VMs on the logical network using a public frontend IP.
+
+> [!NOTE]
+> A public IP in multi-rack deployments of Azure Local refers to IP space routable within the customer’s network or, optionally, internet-facing. It differs from public IPs in Azure, which must always be internet routable.
+
+## Key characteristics of a load balancer
+
+- Available as a managed Software Defined Networking (SDN) service. You don't need to install or manage a separate load balancer appliance or design for its high availability.
+- Supports TCP and HTTP health monitoring to check backend availability and ensure traffic is sent only to healthy instances.
+- Supports only IPv4 traffic. IPv6 traffic isn't supported currently.
+- Doesn't support Network Address Translation (NAT), both inbound and outbound. For Source Network Address Translation (SNAT) functionality and outbound connectivity, always use a NAT Gateway.
+
+> [!NOTE]
+> You can use either a load balancer or configure inbound rules on a NAT Gateway to enable inbound connectivity on Azure Local virtual networks. However, we recommend using a load balancer for inbound connectivity.
+
+## Load balancer configurations
+
+Load balancers in Azure Local are available on both virtual networks and logical networks.
+
+### On virtual networks
+
+Azure Local supports both public and internal load balancers on virtual networks. Multiple load balancers can reside in the same virtual network, but all must be assigned to a single delegated subnet. When setting up the first load balancer, use an empty subnet with no other user resources such as NICs or VMs.
+
+- To create an internal load balancer, provide the delegated subnet information (an empty subnet if it's the first instance). A private IP address from this subnet is assigned to the load balancer.
+
+- To create a public load balancer, provide the Azure Resource Manager (ARM) ID of a public IP resource in addition to the delegated subnet. The instance is assigned both the public IP and a private IP from the subnet for internal communication.
+
+Backend pools must be in the same virtual network but can be across different subnets.
+
+### On logical networks
+
+On logical networks, only public load balancers are supported. To create a load balancer on a logical network, provide a public IP address resource from the same logical network. Backend pools must be in the same logical network.
+
+The following table show the configuration parameters for different types of load balancers:
+
+| Parameter | Public load balancer on virtual network | Internal load balancer on virtual network | Load balancers on logical network |
+|--|--|--|--|
+| Frontend-ip-subnet-ids | Required | Required | Omit |
+| Frontend-ip-public-ip-ids | Required<br><br>Must be from the same logical network as the NAT Gateway public IP. | Omit | Required<br><br>Must be from the same logical network. |
+| Backend-pool-virtual-network-ids | Required | Required | Omit |
+| Backend-pool-logical-network-ids | Omit | Omit | Required |