Multiple frontends for Azure Load Balancer

Azure Load Balancer allows you to load balance services on multiple frontend IPs. You can use a public or internal load balancer to load balance traffic across a set of services like virtual machine scale sets or virtual machines (VMs).

This article describes the fundamentals of load balancing across multiple frontend IP addresses. If you only intend to expose services on one IP address, you can find simplified instructions for public or internal load balancer configurations. Adding multiple frontends is incremental to a single frontend configuration. Using the concepts in this article, you can expand a simplified configuration at any time.

When you define an Azure Load Balancer, a frontend and a backend pool configuration are connected with a load balancing rule. The health probe referenced by the load balancing rule is used to determine the health of a VM on a certain port and protocol. Based on the health probe results, new flows are sent to VMs in the backend pool. The frontend is defined using a three-tuple comprised of a frontend IP address (public or internal), a protocol, and a port number from the load balancing rule. The backend pool is a collection of Virtual Machine IP configurations. Load balancing rules can deliver traffic to the same backend pool instance on different ports. This is done by varying the destination port on the load balancing rule.

You can use multiple frontends (and the associated load balancing rules) to load balance to the same backend port or a different backend port. If you want to load balance to the same backend port, you must enable Azure Load Balancer Floating IP configuration as part of the load balancing rules for each frontend.

Add Load Balancer frontend

In this example, add another frontend to your Load Balancer.

1. Sign in to the Azure portal.

2. In the search box at the top of the portal, enter Load balancer. Select Load balancers in the search results.

3. Select myLoadBalancer or your load balancer.

4. In the load balancer page, select Frontend IP configuration in Settings.

5. Select + Add in Frontend IP configuration to add a frontend.

6. Enter or select the following information in Add frontend IP configuration. If myLoadBalancer is a Public Load Balancer:

   Setting	Value
   Name	myFrontend2
   IP Version	Select IPv4 or IPv6.
   IP type	Select IP address or IP prefix.
   Public IP address	Select an existing Public IP address or create a new one.

   If myLoadBalancer is an Internal Load Balancer:

   Setting	Value
   Name	myFrontend2
   IP Version	Select IPv4 or IPv6.
   Subnet	Select an existing subnet.
   Availability zone	Select zone-redundant for resilient applications. You can also select a specific zone.

7. Select Save.

Next you must associate the frontend IP configuration you have created with an appropriate load balancing rule. Refer to Manage rules for Azure Load Balancer for more information on how to do this.

Remove a frontend

In this example, you remove a frontend from your Load Balancer.

1. Sign in to the Azure portal.

2. In the search box at the top of the portal, enter Load balancer. Select Load balancers in the search results.

3. Select myLoadBalancer or your load balancer.

4. In the load balancer page, select Frontend IP configuration in Settings.

5. Select the delete icon next to the frontend you would like to remove.

6. Note the associated resources that will also be deleted. Check the box that says 'I have read and understood that this frontend IP configuration as well as the associated resources listed above will be deleted'

7. Select Delete.

Limitations

• There is a limit on the number of frontends you can add to a Load Balancer. For more information, review the Load Balancer section of the Service limits document for details.
• Public IP addresses have a charge associated with them. For more information, see IP Address pricing

Next steps

• Review Outbound connections to understand the effect of multiple frontends on outbound connection behavior.