I am totally new to Pulumi but like the idea. I have used Ansible a lot on-prem. But I am not sure how Pulumi can be used in an air-gapped on-prem env. Maybe I am missing something obvious here. Are any docs on this?

You still need somewhere to store the state; it doesn’t have to be the online Pulumi SaaS however: https://www.pulumi.com/docs/intro/concepts/state/ I suspect (depending on just how air-gapped you are) that the local filesystem backend might be the move: https://www.pulumi.com/docs/intro/concepts/state/#logging-into-the-local-filesystem-backend

It's K8s on prem