How can I allow port-forwarding for a specific deployment in Kubernetes? - kubernetes

Question

I am trying to allow some users in my org to forward ports to our production namespace in Kubernetes. However, I don't want them to be able to forward ports to all services. I want to restrict access to only certain services. Is this possible?
kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
metadata:
name: allow-port-forward-for-deployment-a
rules:
- apiGroups: [""]
resources: ["pods/portforward"]
verbs: ["get", "list", "create"]
---
kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
name: allow-port-forward-for-deployment-a
namespace: production
subjects:
- kind: User
name: "xyz#org.com"
apiGroup: rbac.authorization.k8s.io
roleRef:
kind: ClusterRole
name: allow-port-forward-for-deployment-a
apiGroup: rbac.authorization.k8s.io
The above set up allows all services, but I don't want that.

Answer 1

I believe you can't. According to the docs
Resources can also be referred to by name for certain requests through
the resourceNames list. When specified, requests can be restricted to
individual instances of a resource. To restrict a subject to only
“get” and “update” a single configmap, you would write:
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
namespace: default
name: configmap-updater
rules:
- apiGroups: [""]
resources: ["configmaps"]
resourceNames: ["my-configmap"]
verbs: ["update", "get"]
Note that create requests
cannot be restricted by resourceName, as the object name is not known
at authorization time. The other exception is deletecollection.
Since you want to give the user permissions to create the forward ports, I don't think you can.

Answer 2

These rules worked for me
kind: Role
apiVersion: rbac.authorization.k8s.io/v1
metadata:
namespace: default
name: port-forward
rules:
- apiGroups: [""]
resources: ["pods/portforward"]
verbs: ["get", "create"]
- apiGroups: [""]
resources: ["pods", "services"]
verbs: ["get", "list"]

Answer 3

Assuming users already have access to your kubernetes cluster and relevant namespace. They can simply port-forward local port to a pod (resource) port.
How can you do this?
kubectl port-forward <POD_NAME> <LOCAL_PORT>:<POD_PORT>
See Documentation
Quoting from the document - kubectl port-forward allows using resource name, such as a pod name, to select a matching pod to port forward to since Kubernetes v1.10.
Refer this article if you wish, this nicely explains when you would need RBAC vs kubectl port-forward
RBAC could have been useful only when, you wanted person or a group of people only to port-forward for any services in a relevant namespace in your kubernetes cluster.

Answer 4

Workaround A: StatefulSets and resourceNames
It is possible to restrict port forwarding to a pod with a specific name. resourceNames refer to resources, not subresources:
kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
metadata:
name: allow-port-forward-for-deployment-a
rules:
- apiGroups: [""]
resources: ["pods/portforward"]
resourceNames: ["my-app"]
verbs: ["create"]
A StatefulSet generates predictable pod names, but is different from a ReplicaSet and might not fit your use case.
Workaround B: Jump pod and NetworkPolicy
Sketch:
A StatefulSet that runs kubectl port-forward services/my-service inside the cluster (JUMP).
A NetworkPolicy which restricts traffic from pods belonging to JUMP to the target service
RBAC which restricts creation of subresource portforward to the pods of JUMP up to a predefined maximum number of replicas resourceNames: ["jump-0", "jump-1", ..., "jump-N"].