openova/platform/cilium

Cilium

Unified CNI + Service Mesh for Kubernetes with eBPF.

Status: Accepted | Updated: 2026-02-07

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Overview

Cilium provides both Container Network Interface (CNI) and Service Mesh capabilities in a single, unified solution. It replaces Flannel, kube-proxy, and eliminates the need for a separate service mesh like Istio.

flowchart TB
    subgraph Node["Kubernetes Node"]
        subgraph Cilium["Cilium"]
            Agent[Cilium Agent]
            eBPF[eBPF Programs]
            Hubble[Hubble]
            Envoy[Envoy Proxy<br/>L7 only]
        end

        subgraph Pods["Application Pods"]
            subgraph Pod1["Pod A"]
                App1[Application]
                OTel1[OTel Agent]
            end
            subgraph Pod2["Pod B"]
                App2[Application]
                OTel2[OTel Agent]
            end
        end
    end

    subgraph Observability["Observability"]
        Collector[OTel Collector]
        Grafana[Grafana Stack]
    end

    Agent --> eBPF
    eBPF -->|"L3/L4"| Pod1
    eBPF -->|"L3/L4"| Pod2
    Envoy -->|"L7 when needed"| Pod1
    Envoy -->|"L7 when needed"| Pod2

    OTel1 --> Collector
    OTel2 --> Collector
    Hubble --> Grafana
    Collector --> Grafana

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Why Cilium?

CNI Comparison

Feature	Flannel	Cilium
Basic networking	Yes	Yes
Network policies	No	Yes (L3-L7)
Observability	No	Yes (Hubble)
kube-proxy replacement	No	Yes
eBPF performance	No	Yes
Service mesh	No	Yes (built-in)
L2 LoadBalancer	No	Yes
Gateway API	No	Yes

Service Mesh Comparison

Feature	Istio	Cilium Service Mesh
mTLS	Envoy/ztunnel	eBPF + WireGuard
L7 Policies	Envoy	CiliumEnvoyConfig
Network Policies	Via CNI	Native (eBPF)
Resource Overhead	Medium-High	Low
Observability	Envoy metrics	Hubble + OTel
CNI Integration	Separate	Unified
Complexity	High	Medium

Key Finding: OTel Independence

OpenTelemetry auto-instrumentation is independent of the service mesh:

Component	Provides
OpenTelemetry	SQL queries, HTTP calls, application traces
Service Mesh	mTLS encryption, L7 routing, network policies

Cilium provides mesh features without sacrificing observability - OTel handles application tracing regardless of mesh choice.

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Features

CNI Features

Feature	Purpose
kubeProxyReplacement	Replace kube-proxy with eBPF
hubble	Network observability
hubble.relay	Metrics export to Grafana
gatewayAPI	Gateway API for ingress
encryption	WireGuard-based mTLS
envoy	L7 traffic management
l2announcements	L2 LoadBalancer for bare-metal

Service Mesh Capabilities

Capability	How Cilium Provides It
mTLS	WireGuard encryption (transparent)
L7 Policies	CiliumEnvoyConfig + Network Policies
Traffic Management	Gateway API (HTTPRoute, GRPCRoute)
Observability	Hubble metrics, flows, traces
Circuit Breaker	CiliumEnvoyConfig outlier detection
Retries	HTTPRoute retry policies

---

Configuration

Helm Values

# values.yaml
kubeProxyReplacement: true
k8sServiceHost: ${API_SERVER_IP}
k8sServicePort: 6443

# Service Mesh features
authentication:
  mutual:
    spire:
      enabled: false  # Using Cilium native

encryption:
  enabled: true
  type: wireguard

# L7 proxy
envoy:
  enabled: true

# Hubble observability
hubble:
  enabled: true
  relay:
    enabled: true
  ui:
    enabled: true
  metrics:
    enabled:
      - dns
      - drop
      - tcp
      - flow
      - icmp
      - http

# Gateway API
gatewayAPI:
  enabled: true

# L2 LoadBalancer (optional)
l2announcements:
  enabled: true

---

Network Policies

mTLS (Mutual TLS)

apiVersion: cilium.io/v2
kind: CiliumNetworkPolicy
metadata:
  name: require-mtls
spec:
  endpointSelector:
    matchLabels:
      app: my-service
  ingress:
    - fromEndpoints:
        - matchLabels:
            app: allowed-client
      authentication:
        mode: required

L7 HTTP Policies

apiVersion: cilium.io/v2
kind: CiliumNetworkPolicy
metadata:
  name: http-policy
spec:
  endpointSelector:
    matchLabels:
      app: api-service
  ingress:
    - fromEndpoints:
        - matchLabels:
            app: frontend
      toPorts:
        - ports:
            - port: "8080"
              protocol: TCP
          rules:
            http:
              - method: GET
                path: "/api/v1/.*"
              - method: POST
                path: "/api/v1/users"

---

Gateway API

Cilium replaces traditional ingress controllers with Gateway API:

apiVersion: gateway.networking.k8s.io/v1
kind: Gateway
metadata:
  name: cilium-gateway
spec:
  gatewayClassName: cilium
  listeners:
    - name: https
      port: 443
      protocol: HTTPS
      tls:
        mode: Terminate
        certificateRefs:
          - name: tls-secret
---
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: app-route
spec:
  parentRefs:
    - name: cilium-gateway
  hostnames:
    - "app.example.com"
  rules:
    - matches:
        - path:
            type: PathPrefix
            value: /api
      backendRefs:
        - name: api-service
          port: 8080
      timeouts:
        request: 30s
      retry:
        attempts: 3
        backoff: 100ms

---

Resilience Patterns

Circuit Breaker Tiers

Service Tier	consecutiveErrors	baseEjectionTime	maxEjectionPercent
Critical	3	30s	50%
Standard	5	30s	50%
Background	10	60s	75%

Standard Service Circuit Breaker

apiVersion: cilium.io/v2
kind: CiliumEnvoyConfig
metadata:
  name: service-circuit-breaker
spec:
  services:
    - name: my-service
      namespace: default
  resources:
    - "@type": type.googleapis.com/envoy.config.cluster.v3.Cluster
      name: my-service
      connect_timeout: 5s
      circuit_breakers:
        thresholds:
          - priority: DEFAULT
            max_connections: 100
            max_pending_requests: 100
            max_requests: 1000
            max_retries: 3
      outlier_detection:
        consecutive_5xx: 5
        interval: 10s
        base_ejection_time: 30s
        max_ejection_percent: 50

Critical Service (Database Proxy)

apiVersion: cilium.io/v2
kind: CiliumEnvoyConfig
metadata:
  name: db-proxy-circuit-breaker
spec:
  services:
    - name: db-proxy
      namespace: default
  resources:
    - "@type": type.googleapis.com/envoy.config.cluster.v3.Cluster
      name: db-proxy
      connect_timeout: 3s
      circuit_breakers:
        thresholds:
          - priority: DEFAULT
            max_connections: 50
            max_pending_requests: 50
            max_retries: 2
      outlier_detection:
        consecutive_5xx: 3
        interval: 5s
        base_ejection_time: 30s
        max_ejection_percent: 50

Timeout Configuration

apiVersion: cilium.io/v2
kind: CiliumEnvoyConfig
metadata:
  name: service-timeouts
spec:
  services:
    - name: my-service
      namespace: default
  resources:
    - "@type": type.googleapis.com/envoy.config.route.v3.RouteConfiguration
      name: my-service-routes
      virtual_hosts:
        - name: my-service
          domains: ["*"]
          routes:
            - match:
                prefix: "/"
              route:
                cluster: my-service
                timeout: 30s

---

Health Probes

Probe Type	Purpose	Failure Action
Startup	Wait for initialization	Block traffic
Readiness	Can accept traffic	Remove from LB
Liveness	Process healthy	Restart pod

Standard Configuration

startupProbe:
  httpGet:
    path: /health
    port: 8080
  initialDelaySeconds: 10
  periodSeconds: 5
  failureThreshold: 30

readinessProbe:
  httpGet:
    path: /health/ready
    port: 8080
  periodSeconds: 10
  failureThreshold: 3

livenessProbe:
  httpGet:
    path: /health/live
    port: 8080
  periodSeconds: 20
  failureThreshold: 3

---

SLO-Based Alerting

SLI	Target	Alert Threshold
Availability	99.9%	<99.5% for 5m
Latency (p95)	<500ms	>1s for 5m
Error Rate	<0.1%	>1% for 5m

---

LoadBalancer Options

flowchart TB
    subgraph Options["LoadBalancer Options"]
        subgraph CloudLB["Cloud LB (Recommended)"]
            HetznerLB[Hetzner LB]
            OCILB[OCI LB]
        end

        subgraph K8gbLB["k8gb DNS-based (Free)"]
            K8gb[k8gb GSLB]
            ExternalDNS[ExternalDNS]
        end

        subgraph CiliumLB["Cilium L2 (Single Subnet)"]
            L2[L2 Announcements]
        end
    end

    CloudLB -->|"Best for cloud"| Service[K8s Service]
    K8gbLB -->|"Best for multi-region"| Service
    CiliumLB -->|"Best for single node"| Service

Option	Cost	Multi-Region	Use Case
Cloud LB	Paid	Via k8gb	Production
k8gb DNS-based	Free	Native	Cost-sensitive
Cilium L2	Free	No	Single subnet/dev

---

OpenTelemetry Integration

OTel is configured independently of Cilium:

apiVersion: opentelemetry.io/v1alpha1
kind: Instrumentation
metadata:
  name: auto-instrumentation
  namespace: opentelemetry
spec:
  exporter:
    endpoint: http://collector.opentelemetry.svc:4317
  propagators:
    - tracecontext
    - baggage
  sampler:
    type: parentbased_traceidratio
    argument: "1.0"
  java:
    image: ghcr.io/open-telemetry/opentelemetry-operator/autoinstrumentation-java:latest
  python:
    image: ghcr.io/open-telemetry/opentelemetry-operator/autoinstrumentation-python:latest
  nodejs:
    image: ghcr.io/open-telemetry/opentelemetry-operator/autoinstrumentation-nodejs:latest

Pods opt-in via annotation:

metadata:
  annotations:
    instrumentation.opentelemetry.io/inject-java: "true"

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Observability Stack

Source	Provides
Hubble (Cilium)	Network flows, DNS queries, HTTP metrics (L7), dropped packets
OpenTelemetry	Application traces, SQL queries, HTTP client calls, custom spans
Grafana Stack	Loki (logs), Mimir (metrics), Tempo (traces), dashboards

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Migration from Istio

If migrating from Istio:

1. Install Cilium with service mesh features
2. Remove Istio sidecars (if using sidecar mode)
3. Convert VirtualService → HTTPRoute
4. Convert DestinationRule → CiliumNetworkPolicy + CiliumEnvoyConfig
5. Verify OTel continues working (it's independent)

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Consequences

Positive:

• Unified CNI + service mesh (single component)
• Advanced network policies (L3-L7)
• Network observability via Hubble
• eBPF performance
• kube-proxy replacement
• L2 LoadBalancer option
• Native Kubernetes Gateway API support
• Lower resource overhead than Istio

Negative:

• More complex than Flannel
• eBPF kernel requirements (5.10+)
• Less mature than Istio for some features
• CiliumEnvoyConfig less intuitive than VirtualService

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Part of OpenOva