Configure Azure Load Balancer for an FCI VNN

APPLIES TO: SQL Server on Azure VM

On Azure Virtual Machines, clusters use a load balancer to hold an IP address that needs to be on one cluster node at a time. In this solution, the load balancer holds the IP address for the virtual network name (VNN) used by the clustered resource in Azure.

This article teaches you to configure a load balancer by using the Azure Load Balancer service. The load balancer will route traffic to your failover cluster instance (FCI) with SQL Server on Azure VMs for high availability and disaster recovery (HADR).

For an alternative connectivity option for SQL Server 2019 CU2 and later, consider a distributed network name instead for simplified configuration and improved failover.


Before you complete the steps in this article, you should already have:

Create load balancer

You can create either an internal load balancer or an external load balancer. An internal load balancer can only be from accessed private resources that are internal to the network. An external load balancer can route traffic from the public to internal resources. When you configure an internal load balancer, use the same IP address as the FCI resource for the frontend IP when configuring the load-balancing rules. When you configure an external load balancer, you cannot use the same IP address as the FCI IP address cannot be a public IP address. As such, to use an external load balancer, logically allocate an IP address in the same subnet as the FCI that does not conflict with any other IP address, and use this address as the frontend IP address for the load-balancing rules.

Use the Azure portal to create the load balancer:

  1. In the Azure portal, go to the resource group that contains the virtual machines.

  2. Select Add. Search Azure Marketplace for Load Balancer. Select Load Balancer.

  3. Select Create.

  4. Set up the load balancer by using the following values:

    • Subscription: Your Azure subscription.
    • Resource group: The resource group that contains your virtual machines.
    • Name: A name that identifies the load balancer.
    • Region: The Azure location that contains your virtual machines.
    • Type: Either public or private. A private load balancer can be accessed from within the virtual network. Most Azure applications can use a private load balancer. If your application needs access to SQL Server directly over the internet, use a public load balancer.
    • SKU: Standard.
    • Virtual network: The same network as the virtual machines.
    • IP address assignment: Static.
    • Private IP address: The IP address that you assigned to the clustered network resource.

    The following image shows the Create load balancer UI:

    Set up the load balancer

Configure backend pool

  1. Return to the Azure resource group that contains the virtual machines and locate the new load balancer. You might need to refresh the view on the resource group. Select the load balancer.

  2. Select Backend pools, and then select Add.

  3. Associate the backend pool with the availability set that contains the VMs.

  4. Under Target network IP configurations, select VIRTUAL MACHINE and choose the virtual machines that will participate as cluster nodes. Be sure to include all virtual machines that will host the FCI.

  5. Select OK to create the backend pool.

Configure health probe

  1. On the load balancer pane, select Health probes.

  2. Select Add.

  3. On the Add health probe pane, set the following health probe parameters:

    • Name: A name for the health probe.
    • Protocol: TCP.
    • Port: The port you created in the firewall for the health probe when preparing the VM. In this article, the example uses TCP port 59999.
    • Interval: 5 Seconds.
    • Unhealthy threshold: 2 consecutive failures.
  4. Select OK.

Set load-balancing rules

Set the load-balancing rules for the load balancer.

Set the load-balancing rules for the private load balancer by following these steps:

  1. On the load balancer pane, select Load-balancing rules.

  2. Select Add.

  3. Set the load-balancing rule parameters:

    • Name: A name for the load-balancing rules.
    • Frontend IP address: The IP address for the clustered network resource of the SQL Server FCI.
    • Port: The SQL Server TCP port. The default instance port is 1433.
    • Backend port: The same port as the Port value when you enable Floating IP (direct server return).
    • Backend pool: The backend pool name that you configured earlier.
    • Health probe: The health probe that you configured earlier.
    • Session persistence: None.
    • Idle timeout (minutes): 4.
    • Floating IP (direct server return): Enabled.
  4. Select OK.

Configure cluster probe

Set the cluster probe port parameter in PowerShell.

To set the cluster probe port parameter, update the variables in the following script with values from your environment. Remove the angle brackets (< and >) from the script.

$ClusterNetworkName = "<Cluster Network Name>"
$IPResourceName = "<SQL Server FCI IP Address Resource Name>" 
$ILBIP = "<n.n.n.n>" 
[int]$ProbePort = <nnnnn>

Import-Module FailoverClusters

Get-ClusterResource $IPResourceName | Set-ClusterParameter -Multiple @{"Address"="$ILBIP";"ProbePort"=$ProbePort;"SubnetMask"="";"Network"="$ClusterNetworkName";"EnableDhcp"=0}

The following table describes the values that you need to update:

Value Description
Cluster Network Name The Windows Server Failover Cluster name for the network. In Failover Cluster Manager > Networks, right-click the network and select Properties. The correct value is under Name on the General tab.
SQL Server FCI IP Address Resource Name The resource name for the SQL Server FCI IP address. In Failover Cluster Manager > Roles, under the SQL Server FCI role, under Server Name, right-click the IP address resource and select Properties. The correct value is under Name on the General tab.
ILBIP The IP address of the internal load balancer (ILB). This address is configured in the Azure portal as the ILB's frontend address. This is also the SQL Server FCI's IP address. You can find it in Failover Cluster Manager on the same properties page where you located the <SQL Server FCI/AG listener IP Address Resource Name>.
nnnnn The probe port that you configured in the load balancer's health probe. Any unused TCP port is valid.
"SubnetMask" The subnet mask for the cluster parameter. It must be the TCP IP broadcast address:

After you set the cluster probe, you can see all the cluster parameters in PowerShell. Run this script:

Get-ClusterResource $IPResourceName | Get-ClusterParameter

Modify connection string

For clients that support it, add the MultiSubnetFailover=True to the connection string. While the MultiSubnetFailover connection option is not required, it does provide the benefit of a faster subnet failover. This is because the client driver will attempt to open up a TCP socket for each IP address in parallel. The client driver will wait for the first IP to respond with success and once it does, will then use it for the connection.

If your client does not support the MultiSubnetFailover parameter, you can modify the RegisterAllProvidersIP and HostRecordTTL settings to prevent connectivity delays upon failover.

Use PowerShell to modify the RegisterAllProvidersIp and HostRecordTTL settings:

Get-ClusterResource yourFCIname | Set-ClusterParameter RegisterAllProvidersIP 0  
Get-ClusterResource yourFCIname | Set-ClusterParameter HostRecordTTL 300 

To learn more, see the SQL Server listener connection timeout documentation.


  • Set the MultiSubnetFailover parameter = true in the connection string even for HADR solutions that span a single subnet to support future spanning of subnets without the need to update connection strings.
  • By default, clients cache cluster DNS records for 20 minutes. By reducing HostRecordTTL you reduce the Time to Live (TTL) for the cached record, legacy clients may reconnect more quickly. As such, reducing the HostRecordTTL setting may result in increased traffic to the DNS servers.

Test failover

Test failover of the clustered resource to validate cluster functionality.

Take the following steps:

  1. Connect to one of the SQL Server cluster nodes by using RDP.
  2. Open Failover Cluster Manager. Select Roles. Notice which node owns the SQL Server FCI role.
  3. Right-click the SQL Server FCI role.
  4. Select Move, and then select Best Possible Node.

Failover Cluster Manager shows the role, and its resources go offline. The resources then move and come back online in the other node.

Test connectivity

To test connectivity, sign in to another virtual machine in the same virtual network. Open SQL Server Management Studio and connect to the SQL Server FCI name.


If you need to, you can download SQL Server Management Studio.

Next steps

To learn more, see: