Rudder

Yes, that seems to be an overlooked. It could be done in the same way as ${rudder.node.hostname/etc} works.
But then, I don't know how to use them within ncf-builder.

So, do we want to add a ${rudder.node.prop.FOO} (that will be changed to "bar" if such FOO property is defined on node) ?

See #5225 that expose the problems, the solution used for environment variable in #5449, and the general user story in #3112.

Note that the situation is a little better than environment variable because at least, our properties are clearly defined on the node on Rudder side, and so we don't have to wonder what value we want to use at run time - it's the value that was available when the promise was generated.

+1