When updating an Azure Function your service become unavailable. During a recent deployment we saw a series of error code such as 503, 404, 502, and 401 (in that order). This is unnecessary and violates the widely recognized high availability attribute of serverless services. I recognize that one is able to use a slot and then swap it into the target slot but this should be the default behavior of every slot, including (or especially) the default slot.

Not providing a high availability guarantee by default causes faults unnecessarily and requires every one of your customers to solve/mitigate the circumstance when you could easily, simply, and efficiently solve the problem for every one of your customers in one action.