Network Policies

Network policies are designed by Kubernetes to restrict pod access. It is equivalent to a firewall at the application layer to enhance network security. The capabilities of network policies are determined by the network add-ons available in the cluster.

By default, if a namespace does not have any policy, pods in the namespace accept traffic from any source and send traffic to any destination.

NetworkPolicy rules are classified into the following types:

namespaceSelector: This selects particular namespaces for which all pods should be allowed as ingress sources or egress destinations.
podSelector: This selects particular pods in the same namespace as the NetworkPolicy which should be allowed as ingress sources or egress destinations.
ipBlock: This selects particular IP CIDR ranges to allow as ingress sources or egress destinations. (Only egress support IP address blocks.)

Using Ingress Rules

Using podSelector to specify the access scope

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: test-network-policy
  namespace: default
spec:
  podSelector:                  # The rule takes effect for pods with the role=db label.
    matchLabels:
      role: db
  ingress:                      # This is an ingress rule.
  - from:
    - podSelector:              # Only traffic from the pods with the "role=frontend" label is allowed.
        matchLabels:
          role: frontend
    ports:                      # Only TCP can be used to access port 6379.
    - protocol: TCP
      port: 6379

The following figure shows how podSelector works.

Figure 1 podSelector

Using namespaceSelector to specify the access scope

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: test-network-policy
spec:
  podSelector:                  # The rule takes effect for pods with the role=db label.
    matchLabels:
      role: db
  ingress:                      # This is an ingress rule.
  - from:
    - namespaceSelector:        # Only traffic from the pods in the namespace with the "project=myproject" label is allowed.
        matchLabels:
          project: myproject
    ports:                      # Only TCP can be used to access port 6379.
    - protocol: TCP
      port: 6379

The following figure shows how namespaceSelector works.

Figure 2 namespaceSelector