Kubernetes microsegmentation divides clusters into isolated segments to limit breach blast radius, using workload identity (labels/namespaces) rather than IP addresses. Traditional IP-based firewalls fail in cloud-native environments due to ephemeral pod IPs, lack of contextual identity, and iptables scalability issues. Cilium addresses this by assigning numeric Security Identities to label sets, enabling O(1) policy lookups via eBPF hash maps instead of sequential iptables chains. The guide covers Cilium's advantages over native Kubernetes NetworkPolicy — including Layer 7 API-aware enforcement (HTTP paths, gRPC methods), cluster-wide policies, egress gateways for legacy systems, and host-layer segmentation. A four-phase implementation strategy is outlined: observe traffic with Hubble, refine labels, test in audit mode, then enforce. Compliance benefits for PCI-DSS, SOC2, and GDPR are also discussed.
