Microsoft is upgrading all virtual routers of the hubs of the Virtual WAN in Microsoft Azure from their current Cloud Services infrastructure to deployments based on Virtual Machine Scale Sets (VMSS). This upgrade will now enable the virtual hub router to automatically recognize availability zones. You will only be able to update your virtual hub router if all the resources (gateways/route tables/VNet connections) in your hub are in a succeeded state. Note that since this operation requires the deployment of new VMSS-based virtual hub routers, there will be an expected downtime of 30 minutes per hub. Within a single Virtual WAN resource, it is recommended to update hubs one at a time, instead of updating multiple hubs simultaneously. There will be no routing behavior changes after this update. If the update fails for any reason, your hub will be automatically reverted to the older version to ensure you still have a working setup. Automated migration will be done by Microsoft for all customers; however, customers can choose to update earlier. For more information, see https://docs.microsoft.com/en-us/azure/virtual-wan/virtual-wan-faq#why-am-i-seeing-a-message-and-button-called-update-router-to-latest-software-version-in-portal.
There are two solutions for upgrading the virtual router:
Preferred Solution - Hub Migration
Create a new hub in an existing Virtual WAN, then create a new Network Virtual Appliance (NVA) there and move all sites to the new hub. This is the preferred solution because it has limited downtime and provides rollback capabilities if problems occur. For more information, see How to Create a New Hub in an Existing Virtual WAN to Support the New Microsoft Virtual Router - Preferred Solution.
Alternate Solution - Replacement
Remove the existing Barracuda NVA, update the routing service of the existing hub, and recreate the gateway with a recovery token provided by Barracuda Networks Technical Support. This solution requires fewer configuration steps, but the downtime is longer, and you must contact Barracuda Networks Technical Support to retrieve the recovery token, whereas the preferred solution can be done completely alone. For more information, see How to Update an Existing Virtual WAN Hub to Support the New Microsoft Virtual Router - Alternate Solution.