Deploying Kubernetes Network Policies in Self-Hosted Clusters

In a self-hosted Kubernetes cluster, this default state is dangerous. Without clear Kubernetes Network Policies, every pod can connect to every other pod, and to external services, with no restrictions. For security, stability, and compliance, you need hard boundaries for traffic inside your cluster.

What Kubernetes Network Policies Do
Kubernetes Network Policies define how pods communicate—both with other pods and with external endpoints. They are implemented at the network layer, enforced by the networking plugin (CNI). By default, if you create no policies, all traffic is allowed. Once a policy exists, only the allowed connections are possible.

In a self-hosted setup, you control the cluster, the CNI plugin, and the policy designs. This gives you flexibility, but also requires decisive planning. A managed cloud platform might have guardrails baked in; self-hosted Kubernetes leaves it to you.

Key Steps to Deploy Kubernetes Network Policies in Self-Hosted Clusters

1. Choose a CNI that Supports Network Policies
   Not all CNIs support them. Calico, Cilium, and Weave Net are popular for self-hosted environments. Without policy support, manifests will apply but do nothing.
2. Identify Traffic Flows
   Map out which pods need inbound and outbound connections. Consider namespaces, app tiers, and external service access.
3. Apply a Default Deny Policy
   In each namespace, create a policy that denies all ingress and/or egress by default. This flips the model from “allow all” to “allow only what you define.”
4. Create Allow Policies for Required Communications
   Write precise YAML manifests to allow what’s necessary. Use label selectors to match pods. Keep rules minimal to reduce the attack surface.
5. Test and Iterate
   Apply policies in staging first. Use tools like kubectl exec or netcat to verify allowed and blocked traffic. Adjust as needed.

Common Pitfalls in Self-Hosted Deployments

• Forgetting that Network Policies are namespace-scoped by default.
• Mixing matchLabels across deployments without consistent labeling.
• Not testing egress rules; DNS resolution can break if not explicitly allowed.
• Assuming policies apply cluster-wide without checking the namespace context.

Why This Matters
A compromised pod in a cluster without policies can scan and attack other workloads. Misconfigured policies can also cause outages by blocking required internal traffic. In a self-hosted Kubernetes environment, you are responsible for both ends of this spectrum.

Designing strict yet functional Kubernetes Network Policies in a self-hosted deployment is the difference between controlled, predictable network flows and an exposed, chaotic system. Run them from day one, and treat them as part of your application’s core code—not an afterthought.

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