[UI] Number of nodes not balanced across region if number of nodes are reduced while creating platform (2.8.6.0-b12)

[gautamsomani]

Description

While creating a Universe, after a Provider and Region has been selected, there is an option to increase the number of nodes, just below the Regions text box, as seen in screenshot-1 attached.

By default the number is 3, and if the number is increased, the number of nodes in the "Availability Zone" which is on the right side, also increases, and it increases in a way that number of nodes is almost/exactly distributed among the number of available zones (as seen in screenshot-2. Here the number of node is increased to 6, and each zone gets 2 nodes each. This is balanced, in the context of this ticket).

But after increasing the number if we reduce the number of nodes from the "Nodes" list on the left side, below the "Regions" text box, the number of nodes in the "Availability Zone" does not decrease proportionately or in an overall balanced way. Meaning, it may happen that if there are 3 Zones, one region will have just 1 node while the other 2 zones may have 2 and 3 nodes respectively, as seen in screenshot-3.

In such a case if the Zone with 1 node goes down, then we loose an entire replica, since we do replication at Zone level (Correct me if I am wrong here.)

For example, by default the number of nodes is 3. So each zone gets one 1 node each. Suppose we increase this number to 12, then each zone will get 4 nodes. Now, if we reduce this number to 6, again from Nodes drop down list under "Regions" text box, then Zone 1 may get 2 node, Zone 2 may get 1 node and Zone 3 may get 3 node. This is not balanced. Each zone should get equal or nearly equal number of nodes.

Also, if we further reduce the number of nodes to 3, then a Zone may disappear completely, and the remaining 2 Zones will get 1 and 2 nodes respectively. See screenshot-4.

I know the customer has the option to manually change the numbers from the UI, but if we can reduce the number more intelligently and in a way to maintain balance, it would be nice.