Kubernetes namespaces with RBAC: sufficient for tenant isolation in a public environment?
There's an active SIG devoted to multitenancy so I have a hard time believing that nothing has been written about it in 4 years.
Namespaces are only part of the answer. That isolates kubernetes objects impacting other kubernetes objects, but you also need to worry about shared resources like the ingress namespace. If containers share worker nodes, then there are resource limits to enforce. And the default network model used by kubernetes is flat with DNS exposing services and containers in other namespaces and an open network policy allowing any container to talk to any other container. The kubernetes API is also shared in a multi-tenant environment, allowing a DoS to the kubernetes infrastructure itself. And if users are allowed to run containers with added capabilities, privileged access, host bind mounts, host namespaces, and probably many other features, they can escape the container isolation and get root access on the host running the containers. None of this is trivial to implement securely.