Mastering Network Policies in Kubernetes: Security Without Compromise

Network policies exist to control the flow of traffic to and from your Kubernetes pods, providing a vital layer of security in a microservices architecture. By defining rules at Layers 3 and 4, you can restrict access based on IP addresses and ports, ensuring that only authorized services can communicate with each other. This is especially important in multi-tenant environments where isolation is key to preventing data leaks and unauthorized access.

When you run Cilium on Kubernetes, you can leverage its ability to distribute policies across all nodes automatically. This means you can define a Kubernetes NetworkPolicy for basic L3 and L4 controls, or opt for the more advanced CiliumNetworkPolicy, which allows for Layer 3-7 specifications. To enable Kubernetes ClusterNetworkPolicy support, you must set the --enable-k8s-cluster-network-policy flag to true. Additionally, be cautious with ipBlock rules, as they do not match intra-cluster IPs by default, which could lead to unexpected behavior if not configured correctly.

In production, managing multiple policy types can become complex. You need to pay close attention to how these policies interact, as overlapping rules might create unintended traffic allowances. Starting with Cilium 1.20, you can use Kubernetes ClusterNetworkPolicy, but migrating from CiliumClusterwideNetworkPolicy requires careful planning. Always install the Custom Resource Definition (CRD) from sigs.k8s.io/network-policy-api to get started.