I'm trying to configure rolling website updates to an IIS web farm to enable zero downtime deployments. I can't identify a reasonable way to stop traffic being routed from Application Gateway to a VMSS instance.
Any Application Gateway updates seem to take 45 minutes so that isn't really feasible.
If I set a short health probe poll and unhealthy threshold limit for the Application Gateway, and use an app_offline.htm file so IIS responds with an error, users may still receive the app_offline.htm page before the Application Gateway deems the instance unhealthy.
I'd really prefer to tell the Application Gateway to stop serving traffic to instance x, update the instance, then tell Application Gateway to resume routing traffic to the instance.
Am I missing something here? Is there a way to perform a rolling zero-downtime deployment with Application Gateways?