Example for targeting policy based on guest name?

[inflatador]

MoM's policy DSL is extremely powerful, but I've been struggling with how to apply it as the documentation is pretty minimal.

I've been trying to write a policy that is selectively applied based on hostname. I've written a helper function (see below), but I can't figure out how to apply it.

# Kubernetes and nomad are orchestrators, so we don't want to apply the balloon policy to them.
# Set "1" (true) if the host is an orchestrator
(def is_orchestrator (guest)
{ (defvar guest_name (guest.Prop "name"))
    (defvar is_orchestrator 0)
    (if (or (== guest_name "kubernetes.example.com")
        (== guest_name "nomad.example.com"))
        (set is_orchestrator 1)
        is_orchestrator)
}
)

Debug logging shows the value is correctly set. The below result [1, 1, 0, 0] shows that the code finds the 4 guests on the host and correctly sets the is_orchestator value (1 for kubernetes/nomad, 0 for the other hosts):

2024-09-02 17:49:22,183 - mom.Policy - DEBUG - Results: [0.25, 0.1, 0.2, 0.75, 0.01,
'is_orchestrator', 'change_big_enough', 'shrink_guest', 'grow_guest', [1, 1, 0, 0], 0
.2393567666022347, [0, 0, 0, 0]]

I'm stuck at the next step; I can't seem to apply the policy conditionally. Various permutations of if statements/parenthesis end up with arity errors or empty results.

Any suggestions on how to write the policy would be appreciated. I'm happy to make a PR for updating the docs once I have a working example. Thanks for your time!