Minor note: you can have multiple ingress resources for the same hostname. This way you can route some paths to some services in a namespace and other paths to other namespaces.
(Yes, it's confusing. Yes, it can be dangerous)
(Yes, it's confusing. Yes, it can be dangerous)
After reading this gigantic issue (https://github.com/kubernetes/kubernetes/issues/17088), we gave up and just created another GCP project.