• 5 minutes

You can use Load balancing to evenly distribute inbound network traffic across a group of resources or servers. In this scenario, the load balancers are considered front end devices, while the Azure resources to which clients want to connect are the backend pool instances.

In Azure, you manage this inbound traffic with load balancing rules and health probes.

There are two types of load balancers that you can use in Azure, as described in the following table.

Load balancer type	Description
Public load balancer	You use a public load balancer to provide outbound connections for VMs inside your Azure virtual network (VNet). These connections are accomplished by translating their private IP addresses to public IP addresses. You use public load balancers to load balance internet traffic to your VMs.
Internal load balancer	You use an internal (or private) load balancer where private IPs are needed at the frontend only. You use internal load balancers to load balance traffic inside an Azure VNet.

Azure Load Balancer includes a few key components. You can configure these components in your subscription using:

• Azure portal
• Azure CLI
• Azure PowerShell
• Azure Resource Manager templates

Frontend IP configuration

The IP address of your Azure Load Balancer is the point of contact for clients. These IP addresses can be either:

• Public IP addresses
• Private IP addresses

The nature of the IP address determines the type of load balancer created, as described in the following table.

	Public Load Balancer	Internal Load Balancer
Frontend IP configuration	Public IP address	Private IP address
Description	A public load balancer maps the public IP and port of incoming traffic to the private IP and port of the VM. The load balancer then maps traffic the other way around for the response traffic from the VM. You can distribute specific types of traffic across multiple VMs or services by applying load-balancing rules. For example, you can spread the web request traffic across multiple web servers.	An internal load balancer distributes traffic originating on a private IP address to resources that are inside a VNet. Azure restricts access to the frontend IP addresses of a VNet that is load balanced. Front-end IP addresses and VNets are never directly exposed to an internet endpoint. Internal line-of-business (LOB) applications run in Azure, and are accessed either from within Azure or from on-premises resources.
SKUs supported	Basic, Standard	Basic, Standard

Backend pool

A backend pool can be associated to Azure VMs or virtual machine scale set. VMs in the backend pool serve the incoming requests.

When you scale instances up or down, the load balancer instantly reconfigures itself by using automatic reconfiguration. Adding or removing VMs from the backend pool reconfigures the load balancer without additional operations. The load balancer can balance requests to VMs and virtual machine scale set instances that are connected to the same VNet as the load balancer only.

When considering how to design your backend pool, design for the least number of individual backend pool resources to optimize the length of management operations. There's no difference in data plan performance or scale.

Additional reading

Learn more by reviewing the following documents:

• Tutorial: Load balance Windows virtual machines in Azure to create a highly available application with Azure PowerShell
• Multiple frontends for Azure Load Balancer