Merge pull request #246871 from dlepow/stv2

[APIM] stv2 migration back to original subnet

Author: prmerger-automator[bot]

articles/api-management/migrate-stv1-to-stv2.md

@@ -1,12 +1,12 @@
 ---
 title: Migrate Azure API Management instance to stv2 platform  | Microsoft Docs
-description: Follow the steps in this article to migrate your Azure API Management instance from the stv1 compute platform to the stv2 compute platform. Migration steps depend on whether the instance is deployed (injected) in a VNet.
+description: Follow these steps to migrate your Azure API Management instance from the stv1 compute platform to the stv2 compute platform. Migration steps depend on whether the instance is deployed (injected) in a VNet.
 
 author: dlepow
 ms.service: api-management
 ms.custom: devx-track-azurecli
 ms.topic: how-to
-ms.date: 04/17/2023
+ms.date: 07/31/2023
 ms.author: danlep
 ---
 
@@ -22,7 +22,7 @@ For more information about the `stv1` and `stv2` platforms and the benefits of u
 
 > [!IMPORTANT]
 > * Migration is a long-running operation. Your instance will experience downtime during the last 10-15 minutes of migration. Plan your migration accordingly.
-> * The VIP address(es) of your API Management will change if you're using scenario 2 mentioned below (service injected in a VNET). For scenario 1 (not injected in a VNET), the VIP will temporarily change during migration for up to 15 minutes, but the original VIP of the service will be restored at the end of the migration operation. 
+> * The VIP address(es) of your API Management will change if you're using scenario 2 mentioned below (service injected in a VNet). For scenario 1 (not injected in a VNet), the VIP will temporarily change during migration for up to 15 minutes, but the original VIP of the service will be restored at the end of the migration operation. 
 > * Migration to `stv2` is not reversible.
 
 > [!IMPORTANT]
@@ -67,20 +67,22 @@ az rest --method post --uri "$APIM_RESOURCE_ID/migrateToStv2?api-version=2022-08
 
 ## Scenario 2: Migrate a network-injected API Management instance
 
-Trigger migration of a network-injected API Management instance to the `stv2` platform by updating the existing network configuration (see the following section). You can also migrate to the `stv2` platform by enabling [zone redundancy](../reliability/migrate-api-mgt.md).
+Trigger migration of a network-injected API Management instance to the `stv2` platform by updating the existing network configuration to use new network settings (see the following section). After that update completes, as an optional step, you may migrate back to the original VNet and subnet you used.
+
+You can also migrate to the `stv2` platform by enabling [zone redundancy](../reliability/migrate-api-mgt.md).
 
 ### Update VNet configuration
 
 Update the configuration of the VNet in each location (region) where the API Management instance is deployed.
 
 #### Prerequisites
 
-* A new subnet in the current virtual network. (Alternatively, set up a subnet in a different virtual network in the same region and subscription as your API Management instance). A network security group must be attached to the subnet.
+* A new subnet in the current virtual network. (Alternatively, set up a subnet in a different virtual network in the same region and subscription as your API Management instance). A network security group must be attached to the subnet, and [NSG rules](api-management-using-with-vnet.md#configure-nsg-rules) for API Management must be configured.
 
 * A Standard SKU [public IPv4 address](../virtual-network/ip-services/public-ip-addresses.md#sku) resource in the same region and subscription as your API Management instance.
 
 > [!IMPORTANT]
-> When you update the VNet configuration for migration to the `stv2` platform, you must provide a public IP address address resource, or migration won't succeed. In an internal VNet, this public IP address is used only for management operations.
+> When you update the VNet configuration for migration to the `stv2` platform, you must provide a public IP address address resource, or migration won't succeed. In internal VNet mode, this public IP address is used only for management operations.
 
 For details, see [Prerequisites for network connections](api-management-using-with-vnet.md#prerequisites).
 
@@ -97,6 +99,24 @@ To update the existing external or internal VNet configuration:
 
 The virtual network configuration is updated, and the instance is migrated to the `stv2` platform.
 
+### (Optional) Migrate back to original VNet and subnet
+
+You may optionally migrate back to the original VNet and subnet you used in each region before migration to the `stv2` platform. To do so, update the VNet configuration again, this time specifying the original VNet and subnet. As in the preceding migration, expect a long-running operation, and expect the VIP address to change.
+
+#### Prerequisites
+
+* The original subnet and VNet. A network security group must be attached to the subnet, and [NSG rules](api-management-using-with-vnet.md#configure-nsg-rules) for API Management must be configured.
+
+* A new Standard SKU [public IPv4 address](../virtual-network/ip-services/public-ip-addresses.md#sku) resource in the same region and subscription as your API Management instance.
+
+
+#### Update VNet configuration
+
+1. In the [portal](https://portal.azure.com), navigate to your original VNet.
+1. In the left menu, select **Subnets**, and then the original subnet. 
+1. Verify that the original IP addresses were released by API Management. Under **Available IPs**, note the number of IP addresses available in the subnet. All addresses (except for Azure reserved addresses) should be available. If necessary, wait for IP addresses to be released. 
+1. Repeat the migration steps in the preceding section. In each region, specify the original VNet and subnet, and a new IP address resource.
+
 ## Verify migration
 
 To verify that the migration was successful, check the [platform version](compute-infrastructure.md#how-do-i-know-which-platform-hosts-my-api-management-instance) of your API Management instance. After successful migration, the value is `stv2`.