Setting up network policies in Kubernetes involves creating YAML configuration files that define traffic rules between pods and external resources. You'll need a compatible network plugin like Calico or Cilium, then apply policies using kubectl commands to control ingress and egress traffic flows within your cluster.
Understanding Network Policies in Kubernetes Clusters
Network policies in Kubernetes function as firewall rules that control traffic flow between pods, namespaces, and external endpoints. These policies operate at the application layer, allowing you to implement microsegmentation within your cluster architecture.
By default, Kubernetes clusters allow all pod-to-pod communication. Network policies change this behaviour by creating explicit allow or deny rules. They work by selecting pods using labels and defining which traffic sources and destinations are permitted.
Network policies require a compatible Container Network Interface (CNI) plugin to function properly. Popular options include Calico, Cilium, and Weave Net. Without these plugins, network policies remain inactive even when applied to your cluster.
What Are Network Policies and Why Do You Need Them?
Network policies are Kubernetes resources that specify how groups of pods communicate with each other and other network endpoints. They provide microsegmentation capabilities that isolate workloads and reduce attack surfaces within your cluster.
Without network policies, any pod can communicate with any other pod in your cluster. This default "allow-all" behaviour creates security risks, especially in multi-tenant environments or when running untrusted workloads.
Key benefits include:
- Preventing lateral movement during security breaches
- Isolating sensitive applications from general workloads
- Implementing compliance requirements for data protection
- Reducing blast radius of compromised containers
How Do You Create Your First Network Policy?
Creating a network policy starts with defining a YAML manifest that specifies pod selectors and traffic rules. The policy applies to pods matching the specified labels within a particular namespace.
Here's the basic structure:
| Component | Purpose | Required |
|---|---|---|
| metadata | Policy name and namespace | Yes |
| spec.podSelector | Target pods using labels | Yes |
| spec.policyTypes | Ingress, Egress, or both | Yes |
| spec.ingress | Inbound traffic rules | Optional |
| spec.egress | Outbound traffic rules | Optional |
Apply your policy using kubectl apply -f policy.yaml. The policy takes effect immediately for matching pods, blocking traffic that doesn't meet the specified criteria.
What's the Difference Between Ingress and Egress Rules?
Ingress rules control inbound traffic to selected pods, whilst egress rules manage outbound traffic from those pods. Understanding this distinction helps you create comprehensive security policies for your applications.
Ingress rules specify which sources can send traffic to your pods. Sources include other pods (selected by labels), namespaces, or IP address blocks. You can also specify allowed ports and protocols.
Egress rules define where your pods can send traffic. This includes destination pods, namespaces, external IP ranges, and specific ports. Egress policies help prevent data exfiltration and limit external dependencies.
Common patterns include:
- Allow ingress from specific namespaces only
- Permit egress to databases on particular ports
- Block all external egress except DNS queries
- Allow ingress from load balancer IP ranges
How Do You Troubleshoot Network Policy Issues?
Network policy troubleshooting involves systematic testing of connectivity between pods and validating policy configurations. Start by checking if your CNI plugin supports network policies and whether policies are correctly applied.
Common issues include:
- Missing or incorrect pod labels that don't match selectors
- Overly restrictive policies blocking legitimate traffic
- CNI plugin not supporting network policies
- Namespace isolation preventing cross-namespace communication
Debugging techniques involve using kubectl exec to test connectivity between pods, checking pod labels with kubectl get pods --show-labels, and reviewing policy specifications for syntax errors.
Tools like kubectl describe networkpolicy help identify configuration issues, whilst network debugging pods can test specific connectivity scenarios within your cluster.
Network Policy Best Practices for Production Environments
Production network policies require careful planning to balance security requirements with operational needs. Start with a default-deny policy, then gradually add specific allow rules for required communication paths.
Important considerations include:
- Testing policies in staging environments before production deployment
- Implementing monitoring to detect blocked legitimate traffic
- Using meaningful labels and annotations for policy management
- Regular policy reviews to remove obsolete rules
Performance implications are generally minimal, but complex policies with many rules can impact network throughput. Monitor cluster performance after implementing comprehensive network policies.
Cloud providers offering managed Kubernetes services often provide enhanced networking features and support for network policy implementation. These services can simplify policy management whilst ensuring compatibility with your infrastructure requirements.
Network policies form a critical component of Kubernetes security architecture. When implemented thoughtfully with proper testing and monitoring, they significantly improve your cluster's security posture. At Falconcloud, we support comprehensive Kubernetes deployments with robust networking capabilities to help you implement effective security policies across your containerised applications.