Implementing Zero-Trust Networking

Implementing Zero-Trust Networking

Zero-trust networking assumes no implicit trust between components, requiring explicit authorization for all communications. Network Policies enable zero-trust implementation by denying all traffic by default and explicitly allowing only necessary connections. This approach significantly reduces attack surface and limits lateral movement possibilities for attackers who compromise individual components.

Implementing zero-trust begins with creating default deny policies for all namespaces. These policies block all ingress and egress traffic unless explicitly allowed by additional policies. Starting with complete isolation forces teams to understand and document all necessary communications, revealing unexpected dependencies and potential security risks.

# Default deny all ingress traffic
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: default-deny-ingress
  namespace: production
spec:
  podSelector: {}  # Apply to all pods in namespace
  policyTypes:
  - Ingress

---
# Default deny all egress traffic
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: default-deny-egress
  namespace: production
spec:
  podSelector: {}  # Apply to all pods in namespace
  policyTypes:
  - Egress
  egress:
  # Allow DNS resolution (required for most apps)
  - to:
    - namespaceSelector:
        matchLabels:
          name: kube-system
    - podSelector:
        matchLabels:
          k8s-app: kube-dns
    ports:
    - protocol: UDP
      port: 53
    - protocol: TCP
      port: 53

Progressive policy development enables gradual zero-trust adoption without disrupting existing applications. Teams can implement policies in monitoring mode using CNI-specific features, observing traffic patterns before enforcement. This approach reveals actual communication patterns, which often differ from documented architectures. Tools like Hubble (Cilium) or Calico's flow logs provide visibility into network communications.