Testing Kubernetes Network Policies with Socat

Kubernetes Network Policies define which pods can talk to each other and to the outside world. They let you lock down services, block lateral movement, and enforce zero trust inside your cluster. Without them, any pod can connect anywhere. With them, you control namespace boundaries at the network layer.

A network policy in Kubernetes works by matching pods with labels, then applying ingress and egress rules. These rules describe allowed traffic by protocol, port, and peer. You can block all by default, then allow only specific flows. This is enforced by the underlying CNI plugin, so behavior depends on your network provider.

Socat is a multipurpose relay tool. In the context of Kubernetes, it’s often used for testing and troubleshooting network connectivity between pods or services. Run Socat inside a pod to proxy traffic, listen on a port, or forward data to another address. This is especially useful for verifying that a Network Policy is behaving as expected.

For example, you might deploy two pods in separate namespaces. Apply a Kubernetes Network Policy to block TCP traffic between them. Then start Socat in one pod to listen on a specified port. In the other pod, try to connect. If the connection times out, the policy works. If it succeeds, you need to adjust the specification.

Common mistakes include forgetting to create a default deny policy, not matching pod labels correctly, or neglecting egress restrictions. Another frequent issue is testing in a cluster where the network plugin does not implement Network Policies. Always confirm that your CNI supports the features you need.

To integrate secure testing into CI/CD, you can write automated checks that spin up pods, apply policies, run Socat probes, and assert expected results. This reduces drift between intended and actual network rules, making it harder for misconfigurations to slip into production.

Strong network segmentation in Kubernetes isn’t optional. Network Policies with verified behavior keep services contained, data safe, and attackers stalled. Socat makes validation fast and concrete.

Want to see this in action and test policies in minutes? Try it now at hoop.dev and watch your Kubernetes Network Policies with Socat come alive.