The Consumption Plan for Azure Functions is quite ideal, with its pleasant pricing and automatic scaling. However, I haven't found much information about High Availability with such a plan.
Let's consider a scenario. Imagine that, based on the load, there is currently one instance of the function app running. Then there is a problem in that data center. The consumption plan only scales out based on load. I can find no guarantees that a new instance will be added in this scenario, let alone that downtime will be prevented.
I'm aware that we could use Azure Front Door, with two separate function apps behind it. However, it appears that we must manage those function apps separately. That is a hassle. Swapping slots twice, remembering to change app settings in two places... That's no good.
What I'd like to achieve is something like Azure SQL in its Premium or Business-Critical tier, preferably with zone-redundant configuration. The diagram here shows how that works: https://learn.microsoft.com/en-us/azure/sql-database/sql-database-high-availability#zone-redundant-configuration
In simple terms, there is a primary replica with automatic failover to a secondary replica in the same data center, and also automatic failover to secondary replicas in two different data centers within the availability zone.
Notice how there is no manual management of the secondary replicas, since they are simply replicated from the primary.
How much of this can we achieve with Azure Functions, and how?
