Azure SQL Managed Instance connection types
Applies to: 
Azure SQL Managed Instance
This article explains how clients connect to Azure SQL Managed Instance depending on the connection type. Script samples to change connection types are provided below, along with considerations related to changing the default connectivity settings.
Connection types
Azure SQL Managed Instance's VNet-local endpoint supports the following two connection types:
- Redirect (recommended): This is the preferred way for SQL clients to connect to managed instances. With redirect, clients establish connections directly to the node hosting the database. To enable redirect, you need to configure firewalls and Network Security Group (NSG) rules to allow inbound access on ports 1433 and port range 11000-11999. Redirect exhibits superior latency and throughput performance compared to proxy. Redirect also minimizes the impact of planned maintenance events of the gateway component, since redirect connections, once established, have no dependency on the gateway. Redirection capability depends on SQL drivers to understand TDS (Tabular Data Stream) 7.4 or newer. TDS 7.4 was first published with Microsoft SQL Server 2012, so any client newer than that will work.
- Proxy (default): This is the legacy connectivity mechanism meant to support SQL drivers that implement TDS versions older than 7.4. In this mode, all connections are proxied through the internal gateway and only the port 1433 is required to be open. In proxy method, the gateways process the instruction to locate the primary SQL replica node to forward the connection. Depending on the nature of this workload, gateways can bottleneck connectivity. Proxy mode can severely degrade the latency and lower the throughput compared to redirect as it is more susceptible to the loss of live connections due to planned maintenance events of the gateway component. For this reason, we highly recommend you configure all your managed instances to use the redirect connection policy unless your SQL clients do not support TDS redirects.
Note that redirect option only has effect on the VNet-local endpoint. Public endpoints and private endpoints to Azure SQL Managed Instance always operate in proxy mode.
Important
It is highly recommended to configure all managed instances to use the redirect connection policy, except when SQL clients do not support TDS redirects.
Redirect connection type
In the redirect connection type, after the TCP session is established to the SQL engine, the client session obtains the destination virtual IP of the virtual cluster node from the load balancer. Subsequent packets flow directly to the virtual cluster node, bypassing the gateway. The following diagram illustrates this traffic flow.
Important
The redirect connection type only afects the VNet-local endpoint. Connections coming through public and private endpoints are always handled using the proxy connection type regardless of the connection type setting.
Proxy connection type
Warning
Proxy connection type is only recommended for old clients and applications that do not support Tabular Data Stream (TDS) standard 7.4 newer (available since SQL Server 2012). Managed instances should be configured to use the redirect connection type whenever possible.
In the proxy connection type, the TCP session is established using the gateway and all subsequent packets flow through it. The following diagram illustrates this traffic flow.
Changing Connection Type
Using the Portal: To change the Connection Type using the Azure portal, open the Virtual Network page and use the Connection type setting to change the connection type and save the changes.
Script to change connection type settings using PowerShell:
Note
This article uses the Azure Az PowerShell module, which is the recommended PowerShell module for interacting with Azure. To get started with the Az PowerShell module, see Install Azure PowerShell. To learn how to migrate to the Az PowerShell module, see Migrate Azure PowerShell from AzureRM to Az.
The following PowerShell script shows how to change the connection type for a managed instance to Redirect.
Install-Module -Name Az
Import-Module Az.Accounts
Import-Module Az.Sql
Connect-AzAccount
# Get your SubscriptionId from the Get-AzSubscription command
Get-AzSubscription
# Use your SubscriptionId in place of {subscription-id} below
Select-AzSubscription -SubscriptionId {subscription-id}
# Replace {rg-name} with the resource group for your managed instance, and replace {mi-name} with the name of your managed instance
$mi = Get-AzSqlInstance -ResourceGroupName {rg-name} -Name {mi-name}
$mi = $mi | Set-AzSqlInstance -ProxyOverride "Redirect" -force