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securitycritical PriorityID: cilium-ebpf-zero-trust-microsegmentation-standard

Deterministic eBPF Cilium Kernel-Level Zero-Trust Microsegmentation

Enforces deterministic, kernel-enforced Layer 3 to Layer 7 workload identity isolation and egress verification via Cilium eBPF without Envoy sidecar overhead. Mandates socket-level BPF program verification (sockops, tc) coupled with CiliumNetworkPolicy (CNP) and CiliumClusterwideNetworkPolicy (CCNP) to eliminate non-deterministic egress, DNS spoofing, and sidecar latency amplification.

Prohibited Anti-Pattern: Over-Permissive CIDR Whitelisting and Unverified DNS Egress in Pod Network Namespaces

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---
description: Deterministic eBPF Cilium Kernel-Level Zero-Trust Microsegmentation - Enforces deterministic, kernel-enforced Layer 3 to Layer 7 workload identity isolation and egress verification via Cilium eBPF without Envoy sidecar overhead. Mandates socket-level BPF program verification (sockops, tc) coupled with CiliumNetworkPolicy (CNP) and CiliumClusterwideNetworkPolicy (CCNP) to eliminate non-deterministic egress, DNS spoofing, and sidecar latency amplification.
globs: k8s/**/*.yaml, deploy/**/*.yaml, infra/**/*.tf, helm/**/*.yaml, src/network/**/*.go
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/cilium-ebpf-zero-trust-microsegmentation-standard"
---

# Deterministic eBPF Cilium Kernel-Level Zero-Trust Microsegmentation

> **Severity**: CRITICAL | **Category**: security
> **Anti-Pattern Warning**: Over-Permissive CIDR Whitelisting and Unverified DNS Egress in Pod Network Namespaces

## System Constraints
You are a Principal Security Architect and Systems Engineer specializing in eBPF and Cilium kernel-level networking. Enforce strict, verifiable zero-trust microsegmentation rules directly inside Linux kernel execution paths (TC and sockops). Reject any policy that relies on standard IP/CIDR blocks for internal cluster traffic, non-FQDN egress wildcards, or unvalidated Layer 7 protocols. Ensure all network egress is pinned to cryptographic identity primitives and deterministic FQDN proxies managed via Cilium eBPF maps.

## Strict Guidelines
- Engineers MUST ALWAYS declare default-deny ingress and egress rules using `CiliumNetworkPolicy` or `CiliumClusterwideNetworkPolicy` for every production workload.
- Engineers MUST NOT rely on raw IP CIDRs for internal Kubernetes pod-to-pod communication; identity MUST be derived deterministically from cryptographic pod labels (`k8s:io.kubernetes.pod.namespace`, `k8s:app.kubernetes.io/name`).
- Services MUST enforce L7 egress restrictions (HTTP/gRPC methods, paths, and headers) strictly using Cilium eBPF L7 rules with `toFQDNs` and `toEndpoints`, ensuring Envoy is invoked solely at node-level egress gateways when L7 inspection is required, avoiding sidecar-per-pod latency injection.
- Components NEVER permit raw DNS bypass; all outbound DNS queries MUST be intercepted by Cilium eBPF sockops programs targeting trusted in-cluster CoreDNS endpoints with explicit `toPorts.rules.dns` regex restrictions.
- Network policies MUST explicitly declare TLS SNI matches or mutual authentication (mTLS via Cilium SPIFFE/SPIRE integration) without deploying user-space proxy containers into application pods.

## Bad vs Good Implementations
### CiliumNetworkPolicy L3-L7 Egress Lockdown with FQDN and Path Verification

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Standard Kubernetes NetworkPolicy relies on crude L3/L4 IP CIDRs. Permitting 0.0.0.0/0 on port 443 allows compromised pods to exfiltrate data to arbitrary external hosts and does not inspect DNS requests or L7 application protocols at the kernel boundary.
```yaml
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: payment-service-egress
  namespace: payments
spec:
  podSelector:
    matchLabels:
      app: payment-service
  policyTypes:
  - Egress
  egress:
  # ANTI-PATTERN: Wide-open CIDR allowing data exfiltration;
  # no DNS-level pinning, no L7 method/path verification, bypassed kernel tracking
  - to:
    - ipBlock:
        cidr: 0.0.0.0/0
    ports:
    - protocol: TCP
      port: 443
```

#### Production Standard (Correct)
> **Standard**: Uses CiliumNetworkPolicy to intercept UDP 53 directly via eBPF, dynamically populating the kernel FQDN cache exclusively for api.stripe.com. Restricts port 443 egress to explicit HTTP POST transactions targeting /v1/charges without requiring a sidecar proxy inside the pod.
```yaml
apiVersion: cilium.io/v2
kind: CiliumNetworkPolicy
metadata:
  name: payment-service-egress
  namespace: payments
spec:
  endpointSelector:
    matchLabels:
      app.kubernetes.io/name: payment-service
  egress:
  # In-cluster CoreDNS resolution restricted via eBPF L7 parser
  - toEndpoints:
    - matchLabels:
        k8s:io.kubernetes.pod.namespace: kube-system
        k8s:k8s-app: kube-dns
    toPorts:
    - ports:
      - port: "53"
        protocol: UDP
      rules:
        dns:
        - matchPattern: "api.stripe.com"
  # L7 egress pinned directly via eBPF-managed FQDN cache and SNI/HTTP limits
  - toFQDNs:
    - matchName: "api.stripe.com"
    toPorts:
    - ports:
      - port: "443"
        protocol: TCP
      rules:
        http:
        - method: "POST"
          path: "^/v1/charges$"
```
Recommended MCP Servers (mcp-serverlist.com)

Equip agent with system tools to verify code for this stack.

Kubernetes Cilium MCP
Validates, queries, and verifies Cilium CRDs (CiliumNetworkPolicy, CiliumClusterwideNetworkPolicy) and inspects Cilium Endpoints in real-time.
Recommended Agent Skills (askills.dev)

Ready-to-use executable skill functions tailored to this stack.

Cilium CLI & Hubble Diagnostics
Inspects kernel BPF maps, validates policy conformance, and conducts zero-overhead packet observability using Hubble.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Deterministic eBPF Cilium Kernel-Level Zero-Trust Microsegmentation

Deterministic eBPF Cilium Kernel-Level Zero-Trust Microsegmentation defines an industrial-grade behavioral standard for security engineering. Enforces deterministic, kernel-enforced Layer 3 to Layer 7 workload identity isolation and egress verification via Cilium eBPF without Envoy sidecar overhead. Mandates socket-level BPF program verification (sockops, tc) coupled with CiliumNetworkPolicy (CNP) and CiliumClusterwideNetworkPolicy (CCNP) to eliminate non-deterministic egress, DNS spoofing, and sidecar latency amplification. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Over-Permissive CIDR Whitelisting and Unverified DNS Egress in Pod Network Namespaces Without an explicit system instruction file, developers spend hours debugging silent failures.
Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure ModeAI Symptom (The Anti-Pattern)SeverityProduction Impact & Remedy
AI Hallucination & Deprecation DriftOver-Permissive CIDR Whitelisting and Unverified DNS Egress in Pod Network NamespacesCritical
Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production.
Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture InconsistencyAI assistants produce mixed paradigms across files, creating fragmented codebase conventions.Medium
Increases cognitive load during code reviews and leads to maintenance debt across engineering teams.
Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.
Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

1

Engineers MUST ALWAYS declare default-deny ingress and egress rules using `CiliumNetworkPolicy` or `CiliumClusterwideNetworkPolicy` for every production workload.

Engineers MUST ALWAYS declare default-deny ingress and egress rules using `CiliumNetworkPolicy` or `CiliumClusterwideNetworkPolicy` for every production workload.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
2

Engineers MUST NOT rely on raw IP CIDRs for internal Kubernetes pod-to-pod communication

Engineers MUST NOT rely on raw IP CIDRs for internal Kubernetes pod-to-pod communication; identity MUST be derived deterministically from cryptographic pod labels (`k8s:io.kubernetes.pod.namespace`, `k8s:app.kubernetes.io/name`).

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
3

Services MUST enforce L7 egress restrictions (HTTP/gRPC methods, paths, and headers) strictly using Cilium eBPF L7 rules with `toFQDNs` and `toEndpoints`, ensuring Envoy is invoked solely at node-level egress gateways when L7 inspection is required, avoiding sidecar-per-pod latency injection.

Services MUST enforce L7 egress restrictions (HTTP/gRPC methods, paths, and headers) strictly using Cilium eBPF L7 rules with `toFQDNs` and `toEndpoints`, ensuring Envoy is invoked solely at node-level egress gateways when L7 inspection is required, avoiding sidecar-per-pod latency injection.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
4

Components NEVER permit raw DNS bypass

Components NEVER permit raw DNS bypass; all outbound DNS queries MUST be intercepted by Cilium eBPF sockops programs targeting trusted in-cluster CoreDNS endpoints with explicit `toPorts.rules.dns` regex restrictions.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
5

Network policies MUST explicitly declare TLS SNI matches or mutual authentication (mTLS via Cilium SPIFFE/SPIRE integration) without deploying user-space proxy containers into application pods.

Network policies MUST explicitly declare TLS SNI matches or mutual authentication (mTLS via Cilium SPIFFE/SPIRE integration) without deploying user-space proxy containers into application pods.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
Technical Questions & Answers

Frequently Asked Technical Questions

Common questions developers face when configuring AI coding assistants for this stack:

Q:Why is Deterministic eBPF Cilium Kernel-Level Zero-Trust Microsegmentation critical for AI coding assistants?

Enforces deterministic, kernel-enforced Layer 3 to Layer 7 workload identity isolation and egress verification via Cilium eBPF without Envoy sidecar overhead. Mandates socket-level BPF program verification (sockops, tc) coupled with CiliumNetworkPolicy (CNP) and CiliumClusterwideNetworkPolicy (CCNP) to eliminate non-deterministic egress, DNS spoofing, and sidecar latency amplification. Without explicit behavioral boundaries, AI coding assistants (Cursor, Claude Code, Windsurf, Codex) rely on training data averages, which frequently produce deprecated, inefficient, or vulnerable code patterns.

Q:How does adopting this rule prevent AI hallucinations?

This rule explicitly declares what the AI must avoid (Over-Permissive CIDR Whitelisting and Unverified DNS Egress in Pod Network Namespaces) and prescribes verified positive examples. Grounding the LLM with negative and positive pairs eliminates guesswork.

Q:Which AI coding environments are supported?

This specification is multi-platform compatible: Cursor (.cursor/rules/*.mdc & .cursorrules), Anthropic Claude Code (CLAUDE.md), Windsurf (.windsurfrules), Codex / Cline (AGENTS.md), and GitHub Copilot (.github/copilot-instructions.md).

Q:Can I combine this rule with other technology stacks?

Yes. Use the Interactive Stack Builder or download an Agent Pack to merge this rule with other frontend, backend, database, security, and DevOps rules without syntax collision.

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