Whitelist "kube-system" namespace using NetworkPolicy

Question

I have a multi-tenant cluster, where multi-tenancy is achieved via namespaces. Every tenant has their own namespace. Pods from a tenant cannot talk to pods of other tenants. However, some pods in every tenant have to expose a service to the internet, using an Ingress.

This I how far I got (I am using Calico):

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: tenant1-isolate-namespace
  namespace: tenant1
spec:
  policyTypes:
  - Ingress
  podSelector: {} # Select all pods in this namespace
  ingress:
  - from:
    - namespaceSelector:
        matchLabels:
          name: tenant1 # white list current namespace

Deployed for each namespace (tenant1, tenant2, ... ), this limits communication between pods within their namespace. However, this prevents pods from the kube-system namespace to talk to pods in this namespace.

However, the kube-system namespace does not have any labels by default so I can not specifically white list this namespace.

I found a (dirty) workaround for this issue by manually giving it a label:

kubectl label namespace/kube-system permission=talk-to-all

And adding the whitelist rule to the networkpolicy:

...
  - from:
    - namespaceSelector:
        matchLabels:
          permission: talk-to-all # allow namespaces that have the "talk-to-all privilege"

Is there a better solution, without manually giving kube-system a label?

Edit: I tried to additionally add an "OR" rule to specifically allow communication from pods that have the label "app=nginx-ingress", but without luck:

  - from
    ...
    - podSelector:
        matchLabels:
          app: nginx-ingress # Allow pods that have the app=nginx-ingress label

Answer 1

apiVersion: networking.k8s.io/v1

The namespaceSelector is designed to match namespaces by labels only. There is no way to select namespace by name.

The podSelector can only select pods in the same namespace with NetworkPolicy object. For objects located in different namespaces, only selection of the whole namespace is possible.

Here is an example of Kubernetes Network Policy implementation:

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: test-network-policy
  namespace: default
spec:
  podSelector:
    matchLabels:
      role: db
  policyTypes:
  - Ingress
  - Egress
  ingress:
  - from:
    - ipBlock:
        cidr: 172.17.0.0/16
        except:
        - 172.17.1.0/24
    - namespaceSelector:
        matchLabels:
          project: myproject
    - podSelector:
        matchLabels:
          role: frontend
    ports:
    - protocol: TCP
      port: 6379
  egress:
  - to:
    - ipBlock:
        cidr: 10.0.0.0/24
    ports:
    - protocol: TCP
      port: 5978

Follow this link to read a good explanation of the whole concept of Network policy, or this link to watch the lecture.

apiVersion: projectcalico.org/v3

Calico API gives you more options for writing NetworkPolicy rules, so, at some point, you can achieve your goal with less efforts and mind-breaking.

For example, using Calico implementation of Network Policy you can:

• set action for the rule (Allow, Deny, Log, Pass),
• use negative matching (protocol, notProtocol, selector, notSelector),
• apply more complex label selectors(has(k), k not in { ‘v1’, ‘v2’ }),
• combine selectors with operator &&,
• use port range (ports: [8080, "1234:5678", "named-port"]),
• match pods in other namespaces.

But still, you can match namespaces only by labels.

Consider reading Calico documentation for the details.

Here is an example of Calico Network Policy implementation:

apiVersion: projectcalico.org/v3
kind: NetworkPolicy
metadata:
  name: allow-tcp-6379
  namespace: production
spec:
  selector: role == 'database'
  types:
  - Ingress
  - Egress
  ingress:
  - action: Allow
    protocol: TCP
    source:
      selector: role == 'frontend'
    destination:
      ports:
      - 6379
  egress:
  - action: Allow