In a dynamic cloud-based environgment, the number of deploy targets for a certain application can vary by a high degree.
For example we have a web application on AWS that uses Autoscaling group to scale from 4 to 20 servers.
Currently I have window size set to 2 but in reality I’d like to be able to deploy on roughly 25% of the nodes at any given time.
I suspect it can be achieved through the use of variables and script but I think this could be a basic functionality that many could take advantage of.
I can see how this feature could be useful in cases such as your however at the moment as you have discovered there is no built-in mechanism to support this.
I’d advise that you add this suggestion to the uservoice area so that we can keep track of it and gauge how many other users would be helped by such a feature.
In the meantime, you can create a preceding script step that calculates the window size and sets it to an output variable that can ten be bound to the window size of the rolling step.
Let me know if you have any questions regarding this approach.