Mastering Kubernetes Network Policies

How to Use Network Policies in Kubernetes

Kubernetes is an essential tool for managing containerized applications across various cloud environments. Leveraging network policies is crucial for securing Kubernetes clusters, controlling traffic flow, and ensuring isolated environments for your applications. This tutorial will guide you through the steps of implementing network policies in Kubernetes, from setting up the necessary prerequisites to populating your policies and verifying their effectiveness.

Prerequisites

A Kubernetes cluster, version 1.9 or later
kubectl command-line tool configured to communicate with your cluster
Understanding of basic Kubernetes concepts

Setting Up a Basic Network Policy

Network policies are implemented to control access to pods in a cluster. By default, all pods are open to communicate. With network policies, you can restrict or allow specific traffic between pods and external clients.

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-same-namespace
  namespace: default
spec:
  podSelector:
    matchLabels: {}
  policyTypes:
  - Ingress
  ingress:
  - from:
    - podSelector:
        matchLabels: {}

This example policy allows ingress traffic within the same namespace.

Applying a Network Policy

After defining your policy, apply it using kubectl:

kubectl apply -f network-policy.yaml

This applies the policy, effectively managing the ingress traffic as defined.

Advanced Traffic Management

Beyond basic policies, Kubernetes supports more sophisticated traffic controls, such as egress rules and specific traffic port policies. Consider expanding your policies to cover these scenarios for tighter security.

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-egress-to-web
  namespace: default
spec:
  podSelector:
    matchLabels:
      role: frontend
  policyTypes:
  - Egress
  egress:
  - to:
    - ipBlock:
        cidr: 0.0.0.0/0
    ports:
    - protocol: TCP
      port: 80

This advanced policy allows egress only through TCP port 80.

Troubleshooting Common Issues

Policy Not Enforced: Ensure that your chosen Kubernetes network plugin supports network policies (e.g., Calico).
Unexpected Traffic Denial: Review your policy for incorrect selectors or unintended rules that might block traffic.

Summary Checklist

Set up and configure your Kubernetes cluster.
Define and apply basic network policies using YAML.
Expand your policies to include egress and port rules for more complex scenarios.
Troubleshoot and verify policy effectiveness regularly.

For further reading on configuring Kubernetes security features, visit our earlier post on How to Configure RBAC in Kubernetes.