Azure Load Balancer delivers high availability and network performance to your applications. It is a Layer 4 (TCP, UDP) load balancer that distributes incoming traffic among healthy service instances in Cloud Services or VMs defined in a Load-Balanced Set.

It can be configured to:

  • load balance Incoming Internet Traffic to Virtual Machines (VMs). This is known as Internet-Facing Load Balancing.
  • load balance traffic
    • between VMs in a Virtual Network
    • between VMs in Cloud Services
    • between VMs and On-Premises Computers in a Cross-Premises Virtual Network.  This is known as Internal Load Balancing.
  • forward External Traffic to a specific VM.

All resources in the cloud need a Public IP address to be reachable from the Internet.

The cloud infrastructure in Azure uses non-routable IP addresses for its resources. It uses Network Address Translation (NAT) with Public IP addresses to communicate to the Internet.

Automatic Reconfiguration

The Load Balancer automatically reconfigures itself when you scale instances in or out. For example, this reconfiguration can happen when you increase the instance count for Web/Worker Roles in a Cloud Service or when you add additional VMs into the same Load-Balanced Set.

Support for Multiple Load-Balanced IP Addresses for VMs

You can get more than one load-balanced Public IP address assigned to a set of VMs. With this ability, you can host multiple SSL websites and/or multiple SQL Server AlwaysOn Availability Group listeners on the same set of VMs.

Template-Based Deployments through Azure Resource Manager

The Load Balancer can be managed through Azure Resource Manager-based APIs and tools.

For more information: