Custom Constraint: Visit one of the two nodes only

[mertbakir]

I want to add a custom constraint to CVRPTW. Let's say I have 2 nodes and I want only one of them to be visited.
So, whichever of them is visited, other must be dropped without cost.

One step further, let's say we have n(5) nodes and I want at_least k (3) of them to be visited.
I couldn't figure out how to implement such constraints. Any help is appreciated.

[Mizux]

did you try to use routing.AddDisjunction([index_1, index_2,...], penalty, 3) ?