Safely managing Cilium network policies in Kubernetes: Testing and simulation techniques

How do Cilium network policy operations and enforcement modes work? Test environment setup Scenario 1: Applying the first default-deny policy Solution 1. a: Endpoint audit mode Solution 1. b: Policy default-deny mode Scenario 2: Making changes to the existing policies Solution 2. a: L7 allow-all Summary & next steps Posted on November 6, 2025 by Dean Lewis, Isovalent CNCF projects highlighted in this post Network policy changes are among the most frequent operations in a Kubernetes cluster. They are also among the most delicate, as even a small mistake can lead to widespread traffic disruption. This tutorial walks through several methods to make policy management safer, especially in day-2 operations or brownfield deployments where clusters already run critical workloads. It shows how to test and validate changes before enforcing them, helping teams adopt a more reliable approach to policy rollout. By following these steps, you can build confidence in your network policy lifecycle and reduce the likelihood of accidental outages. Cilium network policies build upon Kubernetes NetworkPolicy, extending it with deeper visibility and more flexible rule types. Policies are used to allow or deny traffic based on defined rules, which can apply to ingress, egress, or both. These rules are evaluated at the datapath level, meaning enforcement can take place directly in the kernel through eBPF. Every Cilium-managed endpoint operates under a policy enforcement mode, which defines the default network behavior before and after a policy is applied: Default: All traffic is allowed until an endpoint is selected by a policy.