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Star Wars Demo와 함께 Cilium Network Policy 알아보기 [Cilium Study 2주차]

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Star Wars Demo와 함께 Cilium Network Policy 알아보기 [Cilium Study 2주차]

이번에는 Cilium 공식문서에서 제공하는 Star Wars Demo를 진행하며 Cilium이 어떻게 동작하는지 알아보도록 하겠습니다.

1. Application Topology 개요

Star Wars Application Topology

Cilium Docs - Getting Started with the Star Wars Demo

  • deathstar, tiefighter, xwing 세 가지 마이크로서비스로 구성됩니다.
  • Cilium과 kube-dns가 정상 동작하면 Star Wars Demo 애플리케이션을 배포할 수 있습니다.
  • deathstar는 80번 포트에서 HTTP 웹서버를 제공하며, Kubernetes Service를 통해 두 개의 pod replica로 트래픽이 로드밸런싱됩니다.
  • tiefighter와 xwing은 각각 제국(Empire)과 동맹(Alliance) 우주선이 착륙 요청을 보내는 클라이언트 역할을 합니다.
  • tiefighter와 xwing에 대해 서로 다른 보안 정책을 적용하고, deathstar 착륙 서비스에 대한 접근 제어를 실습할 수 있게 됩니다.

1.1. Demo를 통해 확인할 수 있는 내용

  1. 서비스 디스커버리와 라벨 셀렉터 이해
    • Service가 Selector로 특정 라벨을 가진 pod만 선택해 트래픽을 전달하는 방식 이해
  2. Cilium 네트워크 정책 실습
    • tiefigher는 허용되고 xwing은 차단되는 예시를 기반으로, CiliumNetworkPolicy를 사용한 L3/L4/L7 Layer 수준의 접근 제어 확인
  3. Observability 확인
    • Hubble을 사용해 요청 흐름을 추적, 어떤 정책에 의해 허용 또는 거부되는지 시각화

2. 편의성 설정

실습의 편의를 위해 아래와 같이 Alias를 생성한 뒤, 진행하도록 하겠습니다.

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# cilium 파드 이름
export CILIUMPOD0=$(kubectl get -l k8s-app=cilium pods -n kube-system --field-selector spec.nodeName=k8s-m1 -o jsonpath='{.items[0].metadata.name}')
export CILIUMPOD1=$(kubectl get -l k8s-app=cilium pods -n kube-system --field-selector spec.nodeName=k8s-w1  -o jsonpath='{.items[0].metadata.name}')
export CILIUMPOD2=$(kubectl get -l k8s-app=cilium pods -n kube-system --field-selector spec.nodeName=k8s-w2  -o jsonpath='{.items[0].metadata.name}')
echo $CILIUMPOD0 $CILIUMPOD1 $CILIUMPOD2

# 단축키(alias) 지정
alias c0="kubectl exec -it $CILIUMPOD0 -n kube-system -c cilium-agent -- cilium"
alias c1="kubectl exec -it $CILIUMPOD1 -n kube-system -c cilium-agent -- cilium"
alias c2="kubectl exec -it $CILIUMPOD2 -n kube-system -c cilium-agent -- cilium"

alias c0bpf="kubectl exec -it $CILIUMPOD0 -n kube-system -c cilium-agent -- bpftool"
alias c1bpf="kubectl exec -it $CILIUMPOD1 -n kube-system -c cilium-agent -- bpftool"
alias c2bpf="kubectl exec -it $CILIUMPOD2 -n kube-system -c cilium-agent -- bpftool"

3. Star Wars Demo 배포

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# 배포
❯ kubectl apply -f https://raw.githubusercontent.com/cilium/cilium/1.17.6/examples/minikube/http-sw-app.yaml
service/deathstar created
deployment.apps/deathstar created
pod/tiefighter created
pod/xwing created

# pod status & labels 확인
❯ kubectl get pod --show-labels
NAME                        READY   STATUS    RESTARTS   AGE   LABELS
deathstar-8c4c77fb7-b9qmw   1/1     Running   0          16s   app.kubernetes.io/name=deathstar,class=deathstar,org=empire,pod-template-hash=8c4c77fb7
deathstar-8c4c77fb7-vhj8x   1/1     Running   0          16s   app.kubernetes.io/name=deathstar,class=deathstar,org=empire,pod-template-hash=8c4c77fb7
tiefighter                  1/1     Running   0          16s   app.kubernetes.io/name=tiefighter,class=tiefighter,org=empire
xwing                       1/1     Running   0          16s   app.kubernetes.io/name=xwing,class=xwing,org=alliance

# deathstar deployment, service, endpoints 확인
❯ kubectl get deploy,svc,ep deathstar
NAME                        READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/deathstar   2/2     2            2           55s

NAME                TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)   AGE
service/deathstar   ClusterIP   10.233.25.94   <none>        80/TCP    55s

NAME                  ENDPOINTS                          AGE
endpoints/deathstar   10.233.64.96:80,10.233.65.155:80   55s

# ciliumendpoints 확인 (IPV4 -> Pod IP)
❯ kubectl get ciliumendpoints.cilium.io   
NAME                        SECURITY IDENTITY   ENDPOINT STATE   IPV4            IPV6
deathstar-8c4c77fb7-b9qmw   27476               ready            10.233.64.96    
deathstar-8c4c77fb7-vhj8x   27476               ready            10.233.65.155   
tiefighter                  22234               ready            10.233.65.163   
xwing                       42250               ready            10.233.65.156   

## cilium endpoint list 확인  * 현재 ingress/egress에 Policy가 존재 하지 않음
❯ kubectl exec -it -n kube-system ds/cilium -c cilium-agent -- cilium endpoint list
ENDPOINT   POLICY (ingress)   POLICY (egress)   IDENTITY   LABELS (source:key[=value])                                                       IPv6   IPv4            STATUS
           ENFORCEMENT        ENFORCEMENT
88         Disabled           Disabled          12050      k8s:app.kubernetes.io/component=core                                                     10.233.65.8     ready
                                                           k8s:app.kubernetes.io/instance=harbor
                                                           k8s:app.kubernetes.io/managed-by=Helm
                                                           k8s:app.kubernetes.io/name=harbor
                                                           k8s:app.kubernetes.io/part-of=harbor
                                                           k8s:app.kubernetes.io/version=2.12.2
                                                           k8s:app=harbor
                                                           k8s:chart=harbor
                                                           k8s:component=core
                                                           k8s:heritage=Helm
                                                           k8s:io.cilium.k8s.namespace.labels.kubernetes.io/metadata.name=harbor
                                                           k8s:io.cilium.k8s.policy.cluster=default
                                                           k8s:io.cilium.k8s.policy.serviceaccount=default
                                                           k8s:io.kubernetes.pod.namespace=harbor
                                                           k8s:release=harbor
268        Disabled           Disabled          2793       k8s:io.cilium.k8s.namespace.labels.kubernetes.io/metadata.name=kube-system               10.233.65.168   ready
                                                           k8s:io.cilium.k8s.policy.cluster=default
                                                           k8s:io.cilium.k8s.policy.serviceaccount=coredns
                                                           k8s:io.kubernetes.pod.namespace=kube-system
                                                           k8s:k8s-app=kube-dns
441        Disabled           Disabled          1          reserved:host                                                                                            ready
456        Disabled           Disabled          12733      k8s:app.kubernetes.io/instance=external-secrets                                          10.233.65.108   ready
                                                           k8s:app.kubernetes.io/managed-by=Helm
                                                           k8s:app.kubernetes.io/name=external-secrets-cert-controller
                                                           k8s:app.kubernetes.io/version=v0.14.3
                                                           k8s:helm.sh/chart=external-secrets-0.14.3
                                                           k8s:io.cilium.k8s.namespace.labels.kubernetes.io/metadata.name=external-secrets
                                                           k8s:io.cilium.k8s.namespace.labels.name=external-secrets
                                                           k8s:io.cilium.k8s.policy.cluster=default
                                                           k8s:io.cilium.k8s.policy.serviceaccount=external-secrets-cert-controller
                                                           k8s:io.kubernetes.pod.namespace=external-secrets
...
...


## 각 pod가 존재하는 Node의 endpoint list 확인
c0 endpoint list
c1 endpoint list
c2 endpoint list

4. Check Current Access

deathstar 서비스는 org=empire 라벨이 붙은 함선만 착륙 요청을 허용해야 합니다.

하지만 아직 CiliumNetworkPolicy 같은 정책을 적용하지 않았기 때문에, org=alliance(xwing)나 org=empire(tiefighter) 여부와 관계없이 모든 함선이 착륙을 요청할 수 있습니다.

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## 아래 출력에서 xwing 와 tiefighter 의 IDENTITY 메모
❯ c1 endpoint list | grep -iE 'xwing|tiefighter|deathstar'
786        Disabled           Disabled          27476      k8s:app.kubernetes.io/name=deathstar                                                     10.233.65.155   ready
                                                           k8s:class=deathstar                                                            
1585       Disabled           Disabled          42250      k8s:app.kubernetes.io/name=xwing                                                         10.233.65.156   ready
                                                           k8s:class=xwing                                                                
2501       Disabled           Disabled          22234      k8s:app.kubernetes.io/name=tiefighter                                                    10.233.65.163   ready
                                                           k8s:class=tiefighter                                                           

❯ c2 endpoint list | grep -iE 'xwing|tiefighter|deathstar'
169        Disabled           Disabled          27476      k8s:app.kubernetes.io/name=deathstar                                                       10.233.64.96    ready
                                                           k8s:class=deathstar    

XWING_ID=42250
TIEFIGHTER_ID=22234
DEATHSTAR_ID=27476

# 모니터링 준비 : 터미널 1개
❯ hubble observe -f --identity 42250 --identity 22234 --identity 27476

## xwing -> deathstar
❯ kubectl exec xwing -- curl -s -XPOST deathstar.default.svc.cluster.local/v1/request-landing
Ship landed

## tiefighter -> deathstar
❯ kubectl exec tiefighter -- curl -s -XPOST deathstar.default.svc.cluster.local/v1/request-landing
Ship landed

## 확인 xwing(42250) -> deathstar(27476)
Jul 25 13:21:11.765: default/xwing:59516 (ID:42250) -> 169.254.25.10:53 (host) to-stack FORWARDED (UDP)
Jul 25 13:21:11.765: default/xwing:59516 (ID:42250) <- 169.254.25.10:53 (host) to-endpoint FORWARDED (UDP)
Jul 25 13:21:11.765: 169.254.25.10:53 (host) <> default/xwing (ID:42250) pre-xlate-rev TRACED (UDP)
Jul 25 13:21:11.766: 169.254.25.10:53 (host) <> default/xwing (ID:42250) pre-xlate-rev TRACED (UDP)
Jul 25 13:21:11.766: default/xwing:56675 (ID:42250) -> 169.254.25.10:53 (host) to-stack FORWARDED (UDP)
Jul 25 13:21:11.767: 169.254.25.10:53 (host) <> default/xwing (ID:42250) pre-xlate-rev TRACED (UDP)
Jul 25 13:21:11.767: default/xwing:56675 (ID:42250) <- 169.254.25.10:53 (host) to-endpoint FORWARDED (UDP)
Jul 25 13:21:11.767: 169.254.25.10:53 (host) <> default/xwing (ID:42250) pre-xlate-rev TRACED (UDP)
Jul 25 13:21:11.767: default/xwing:46192 (ID:42250) -> 169.254.25.10:53 (host) to-stack FORWARDED (UDP)
Jul 25 13:21:11.768: default/xwing:46192 (ID:42250) <- 169.254.25.10:53 (host) to-endpoint FORWARDED (UDP)
Jul 25 13:21:11.768: 169.254.25.10:53 (host) <> default/xwing (ID:42250) pre-xlate-rev TRACED (UDP)
Jul 25 13:21:11.769: 169.254.25.10:53 (host) <> default/xwing (ID:42250) pre-xlate-rev TRACED (UDP)
Jul 25 13:21:11.769: default/xwing:38587 (ID:42250) -> 169.254.25.10:53 (host) to-stack FORWARDED (UDP)
Jul 25 13:21:11.769: default/xwing:38587 (ID:42250) <- 169.254.25.10:53 (host) to-endpoint FORWARDED (UDP)
Jul 25 13:21:11.769: 169.254.25.10:53 (host) <> default/xwing (ID:42250) pre-xlate-rev TRACED (UDP)
Jul 25 13:21:11.770: 169.254.25.10:53 (host) <> default/xwing (ID:42250) pre-xlate-rev TRACED (UDP)
Jul 25 13:21:11.771: default/xwing (ID:42250) <> 10.233.25.94:80 (world) pre-xlate-fwd TRACED (TCP)
Jul 25 13:21:11.771: default/xwing (ID:42250) <> default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) post-xlate-fwd TRANSLATED (TCP)
Jul 25 13:21:11.771: default/xwing:55456 (ID:42250) -> default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) to-endpoint FORWARDED (TCP Flags: SYN)
Jul 25 13:21:11.771: default/xwing:55456 (ID:42250) <- default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) to-endpoint FORWARDED (TCP Flags: SYN, ACK)
Jul 25 13:21:11.771: default/xwing:55456 (ID:42250) -> default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) to-endpoint FORWARDED (TCP Flags: ACK)
Jul 25 13:21:11.771: default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) <> default/xwing (ID:42250) pre-xlate-rev TRACED (TCP)
Jul 25 13:21:11.771: 10.233.25.94:80 (world) <> default/xwing (ID:42250) post-xlate-rev TRANSLATED (TCP)
Jul 25 13:21:11.771: default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) <> default/xwing (ID:42250) pre-xlate-rev TRACED (TCP)
Jul 25 13:21:11.771: 10.233.25.94:80 (world) <> default/xwing (ID:42250) post-xlate-rev TRANSLATED (TCP)
Jul 25 13:21:11.771: default/xwing:55456 (ID:42250) -> default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) to-endpoint FORWARDED (TCP Flags: ACK, PSH)
Jul 25 13:21:11.771: default/xwing:55456 (ID:42250) <> default/deathstar-8c4c77fb7-vhj8x (ID:27476) pre-xlate-rev TRACED (TCP)
Jul 25 13:21:11.774: default/xwing:55456 (ID:42250) <> default/deathstar-8c4c77fb7-vhj8x (ID:27476) pre-xlate-rev TRACED (TCP)
Jul 25 13:21:11.774: default/xwing:55456 (ID:42250) <> default/deathstar-8c4c77fb7-vhj8x (ID:27476) pre-xlate-rev TRACED (TCP)
Jul 25 13:21:11.775: default/xwing:55456 (ID:42250) <> default/deathstar-8c4c77fb7-vhj8x (ID:27476) pre-xlate-rev TRACED (TCP)
Jul 25 13:21:11.775: default/xwing:55456 (ID:42250) <> default/deathstar-8c4c77fb7-vhj8x (ID:27476) pre-xlate-rev TRACED (TCP)
Jul 25 13:21:11.775: default/xwing:55456 (ID:42250) <- default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) to-endpoint FORWARDED (TCP Flags: ACK, PSH)
Jul 25 13:21:11.775: default/xwing:55456 (ID:42250) -> default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) to-endpoint FORWARDED (TCP Flags: ACK, FIN)
Jul 25 13:21:11.775: default/xwing:55456 (ID:42250) <- default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) to-endpoint FORWARDED (TCP Flags: ACK, FIN)
Jul 25 13:21:11.775: default/xwing:55456 (ID:42250) -> default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) to-endpoint FORWARDED (TCP Flags: ACK)

## 확인 tiefighter(ID:22234) -> deathstar(27476)
Jul 25 13:21:15.569: default/tiefighter:34076 (ID:22234) -> 169.254.25.10:53 (host) to-stack FORWARDED (UDP)
Jul 25 13:21:15.569: 169.254.25.10:53 (host) <> default/tiefighter (ID:22234) pre-xlate-rev TRACED (UDP)
Jul 25 13:21:15.569: 169.254.25.10:53 (host) <> default/tiefighter (ID:22234) pre-xlate-rev TRACED (UDP)
Jul 25 13:21:15.569: default/tiefighter:54684 (ID:22234) -> 169.254.25.10:53 (host) to-stack FORWARDED (UDP)
Jul 25 13:21:15.569: default/tiefighter:34076 (ID:22234) <- 169.254.25.10:53 (host) to-endpoint FORWARDED (UDP)
Jul 25 13:21:15.569: default/tiefighter:54684 (ID:22234) <- 169.254.25.10:53 (host) to-endpoint FORWARDED (UDP)
Jul 25 13:21:15.569: 169.254.25.10:53 (host) <> default/tiefighter (ID:22234) pre-xlate-rev TRACED (UDP)
Jul 25 13:21:15.569: 169.254.25.10:53 (host) <> default/tiefighter (ID:22234) pre-xlate-rev TRACED (UDP)
Jul 25 13:21:15.569: default/tiefighter:54126 (ID:22234) -> 169.254.25.10:53 (host) to-stack FORWARDED (UDP)
Jul 25 13:21:15.570: default/tiefighter:54126 (ID:22234) <- 169.254.25.10:53 (host) to-endpoint FORWARDED (UDP)
Jul 25 13:21:15.570: 169.254.25.10:53 (host) <> default/tiefighter (ID:22234) pre-xlate-rev TRACED (UDP)
Jul 25 13:21:15.570: 169.254.25.10:53 (host) <> default/tiefighter (ID:22234) pre-xlate-rev TRACED (UDP)
Jul 25 13:21:15.570: default/tiefighter:60542 (ID:22234) -> 169.254.25.10:53 (host) to-stack FORWARDED (UDP)
Jul 25 13:21:15.570: default/tiefighter:60542 (ID:22234) <- 169.254.25.10:53 (host) to-endpoint FORWARDED (UDP)
Jul 25 13:21:15.570: 169.254.25.10:53 (host) <> default/tiefighter (ID:22234) pre-xlate-rev TRACED (UDP)
Jul 25 13:21:15.570: 169.254.25.10:53 (host) <> default/tiefighter (ID:22234) pre-xlate-rev TRACED (UDP)
Jul 25 13:21:15.571: default/tiefighter (ID:22234) <> 10.233.25.94:80 (world) pre-xlate-fwd TRACED (TCP)
Jul 25 13:21:15.571: default/tiefighter (ID:22234) <> default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) post-xlate-fwd TRANSLATED (TCP)
Jul 25 13:21:15.571: default/tiefighter:53314 (ID:22234) -> default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) to-network FORWARDED (TCP Flags: SYN)
Jul 25 13:21:15.571: 10.0.0.201:53314 (remote-node) -> default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) to-endpoint FORWARDED (TCP Flags: SYN)
Jul 25 13:21:15.571: 10.0.0.201:53314 (remote-node) <- default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) to-network FORWARDED (TCP Flags: SYN, ACK)
Jul 25 13:21:15.571: default/tiefighter:53314 (ID:22234) <- default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) to-endpoint FORWARDED (TCP Flags: SYN, ACK)
Jul 25 13:21:15.571: default/tiefighter:53314 (ID:22234) -> default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) to-network FORWARDED (TCP Flags: ACK)
Jul 25 13:21:15.571: 10.0.0.201:53314 (remote-node) -> default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) to-endpoint FORWARDED (TCP Flags: ACK)
Jul 25 13:21:15.571: 10.0.0.201:53314 (remote-node) <> default/deathstar-8c4c77fb7-b9qmw (ID:27476) pre-xlate-rev TRACED (TCP)
Jul 25 13:21:15.571: default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) <> default/tiefighter (ID:22234) pre-xlate-rev TRACED (TCP)
Jul 25 13:21:15.571: 10.233.25.94:80 (world) <> default/tiefighter (ID:22234) post-xlate-rev TRANSLATED (TCP)
Jul 25 13:21:15.571: default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) <> default/tiefighter (ID:22234) pre-xlate-rev TRACED (TCP)
Jul 25 13:21:15.571: 10.233.25.94:80 (world) <> default/tiefighter (ID:22234) post-xlate-rev TRANSLATED (TCP)
Jul 25 13:21:15.571: default/tiefighter:53314 (ID:22234) -> default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) to-network FORWARDED (TCP Flags: ACK, PSH)
Jul 25 13:21:15.572: default/tiefighter:53314 (ID:22234) <- default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) to-endpoint FORWARDED (TCP Flags: ACK, PSH)
Jul 25 13:21:15.572: 10.0.0.201:53314 (remote-node) -> default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) to-endpoint FORWARDED (TCP Flags: ACK, PSH)
Jul 25 13:21:15.572: 10.0.0.201:53314 (remote-node) <> default/deathstar-8c4c77fb7-b9qmw (ID:27476) pre-xlate-rev TRACED (TCP)
Jul 25 13:21:15.572: 10.0.0.201:53314 (remote-node) <> default/deathstar-8c4c77fb7-b9qmw (ID:27476) pre-xlate-rev TRACED (TCP)
Jul 25 13:21:15.572: 10.0.0.201:53314 (remote-node) <> default/deathstar-8c4c77fb7-b9qmw (ID:27476) pre-xlate-rev TRACED (TCP)
Jul 25 13:21:15.572: 10.0.0.201:53314 (remote-node) <> default/deathstar-8c4c77fb7-b9qmw (ID:27476) pre-xlate-rev TRACED (TCP)
Jul 25 13:21:15.572: 10.0.0.201:53314 (remote-node) <- default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) to-network FORWARDED (TCP Flags: ACK, PSH)
Jul 25 13:21:15.573: default/tiefighter:53314 (ID:22234) -> default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) to-network FORWARDED (TCP Flags: ACK, FIN)
Jul 25 13:21:15.573: 10.0.0.201:53314 (remote-node) -> default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) to-endpoint FORWARDED (TCP Flags: ACK, FIN)
Jul 25 13:21:15.573: 10.0.0.201:53314 (remote-node) <- default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) to-network FORWARDED (TCP Flags: ACK, FIN)
Jul 25 13:21:15.573: default/tiefighter:53314 (ID:22234) <- default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) to-endpoint FORWARDED (TCP Flags: ACK, FIN)
Jul 25 13:21:15.573: default/tiefighter:53314 (ID:22234) -> default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) to-network FORWARDED (TCP Flags: ACK)
Jul 25 13:21:15.573: 10.0.0.201:53314 (remote-node) -> default/deathstar-8c4c77fb7-b9qmw:80 (ID:27476) to-endpoint FORWARDED (TCP Flags: ACK)

4.1. Traffic Flow 해석

시각주체(엔드포인트 ID)행위의미
13:21:11xwing (42250) -> 169.254.25.10:53to-stack / to‑endpoint UDPxwing Pod가 NodeLocal DNS(169.254.25.10)로 A/AAAA 쿼리 전송, 응답 수신
13:21:11xwing (42250) -> 10.233.25.94:80pre‑xlate‑fwd TRACEDService IP(deathstar)로 나가는 패킷을 캡처 (NAT 전)
13:21:11xwing (42250) -> deathstar‑vhj8x (27476)post‑xlate‑fwd TRANSLATED서비스 IP -> Pod IP로 NAT 완료
13:21:11xwing <-> deathstarFORWARDED TCP(SYN,ACK,PSH,FIN)3‑way handshake, 데이터 전송, 종료까지 정상 연결
13:21:15tiefighter (22234) -> 169.254.25.10:53DNS 쿼리/응답tiefighter도 동일
13:21:15tiefighter (22234) -> deathstar‑b9qmw (27476)to-network / to-endpoint TCPWorker Node1 (10.0.0.201) 경유 후 deathstar Pod까지 정상 통신

5. L3/L4 Network Policy 적용 및 테스트

Cilium을 사용하고 Network Policy를 정의할 때, Endpoint IP는 중요하지 않습니다. Cilium에서는 Endpoint IP가 아닌 Pod 레이블을 기준으로 트래픽을 식별합니다. EndpointSelector로 대상 Pod를 지정하고, fromEndpoints로 허용할 소스 Pod를 지정합니다.

이번에는 org=empire 레이블이 있는 tiefighter만 deathstar의 80/TCP 포트에 접근하도록 허용해보겠습니다. 해당 경우 org=alliance 레이블의 xwing은 차단됩니다.

Cilium은 stateful connection tracking을 수행합니다. Frontend -> Backend 방향이 허용되면, 같은 TCP/UDP 세션의 응답 패킷도 자동으로 허용됩니다. -> 리턴 패킷 자동 허용

5.1. Cilium 및 Kubernetes를 사용한 L4 Network Policy 생성

L4 Layer Policy

L4 Layer Policy

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## Network Policy 생성
apiVersion: "cilium.io/v2"
kind: CiliumNetworkPolicy
metadata:
  name: "rule1"
spec:
  description: "L3-L4 policy to restrict deathstar access to empire ships only"
  endpointSelector:
    matchLabels:
      org: empire
      class: deathstar
  ingress:
  - fromEndpoints:
    - matchLabels:
        org: empire
    toPorts:
    - ports:
      - port: "80"
        protocol: TCP

❯ kubectl apply -f https://raw.githubusercontent.com/cilium/cilium/1.17.6/examples/minikube/sw_l3_l4_policy.yaml

## Network Policy 생성 확인
❯ kubectl get cnp
NAME    AGE   VALID
rule1   38s   True

## Network Policy 설정 확인
❯ k describe cnp rule1
Name:         rule1
Namespace:    default
Labels:       <none>
Annotations:  <none>
API Version:  cilium.io/v2
Kind:         CiliumNetworkPolicy
Metadata:
  Creation Timestamp:  2025-07-26T04:49:46Z
  Generation:          1
  Resource Version:    51853112
  UID:                 f4bf08f4-dd1b-4994-9490-579384037a74
Spec:
  Description:  L3-L4 policy to restrict deathstar access to empire ships only
  Endpoint Selector:
    Match Labels:
      Class:  deathstar
      Org:    empire
  Ingress:
    From Endpoints:
      Match Labels:
        Org:  empire
    To Ports:
      Ports:
        Port:      80
        Protocol:  TCP
Status:
  Conditions:
    Last Transition Time:  2025-07-26T04:49:46Z
    Message:               Policy validation succeeded
    Status:                True
    Type:                  Valid
Events:                    <none>

❯ c1 endpoint list

ENDPOINT   POLICY (ingress)   POLICY (egress)   IDENTITY   LABELS (source:key[=value])                                                       IPv6   IPv4            STATUS
...
786        Enabled            Disabled          27476      k8s:app.kubernetes.io/name=deathstar                                                     10.233.65.155   ready
                                                           k8s:class=deathstar                                                                      
                                                           k8s:io.cilium.k8s.namespace.labels.kubernetes.io/metadata.name=default                   
                                                           k8s:io.cilium.k8s.policy.cluster=default                                                 
                                                           k8s:io.cilium.k8s.policy.serviceaccount=default                                          
                                                           k8s:io.kubernetes.pod.namespace=default                                                  
                                                           k8s:org=empire                                                                           
#


## 모니터링
❯ hubble observe -f --type drop
Jul 26 06:30:51.003: default/xwing:35810 (ID:42250) <> default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) Policy denied DROPPED (TCP Flags: SYN)
Jul 26 06:30:52.030: default/xwing:35810 (ID:42250) <> default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) Policy denied DROPPED (TCP Flags: SYN)

## 접속 확인 (성공) tiefighter(22234) -> deathstar(27476))
❯ kubectl exec tiefighter -- curl -s -XPOST deathstar.default.svc.cluster.local/v1/request-landing
Ship landed

## 접속 확인 (실패) xwing(42250) -> deathstar(27476)
❯ kubectl exec xwing -- curl -s -XPOST deathstar.default.svc.cluster.local/v1/request-landing
command terminated with exit code 28

XWing Dropped

6. L7 Network Policy(HTTP-aware) 적용 및 테스트

마이크로서비스 간 최소 권한 원칙을 지키기 위해서는 L3/L4 수준의 허용 여부만으로는 부족할 수 있습니다. 더 나은 보안을 위해서는 특정 HTTP 메서드와 경로까지 제한해야 합니다. 예시로 deathstar 서비스에는 관리 목적의 API(/v1/exhaust-port 등)가 존재하며, 임의의 함선이 호출해서는 안 됩니다.

L7 동작 처리는 cilium-envoy 데몬셋이 담당 합니다.

Life of a Packet

6.1. 허용되지 않은 요청 확인

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# tiefighter에서 허용되지 않은 PUT 요청 실행 (정책 적용 전)
❯ kubectl exec tiefighter -- curl -s -XPUT deathstar.default.svc.cluster.local/v1/exhaust-port
Panic: deathstar exploded

goroutine 1 [running]:
main.HandleGarbage(0x2080c3f50, 0x2, 0x4, 0x425c0, 0x5, 0xa)
        /code/src/github.com/empire/deathstar/
        temp/main.go:9 +0x64
main.main()
        /code/src/github.com/empire/deathstar/
        temp/main.go:5 +0x85

정책이 없을 때는 위와 같은 민감한 엔드포인트가 호출되어 문제가 발생할 수 있습니다.

6.2. L7 정책 YAML

L7 Layer Policy

L7 Layer Policy

Cilium은 HTTP 계층(L7 Layer) 정책을 적용하여 tiefighter가 접근할 수 있는 URL을 제한할 수 있습니다. 아래 정책은 기존 L3/L4 정책(rule1)을 확장하여, tiefighter가 POST /v1/request-landing 요청만 보낼 수 있도록 제한합니다. 다른 모든 HTTP 호출(ex: PUT /v1/exhaust-port)은 차단됩니다.

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apiVersion: "cilium.io/v2"
kind: CiliumNetworkPolicy
metadata:
  name: "rule1"
spec:
  description: "L7 policy to restrict access to specific HTTP call"
  endpointSelector:
    matchLabels:
      org: empire
      class: deathstar
  ingress:
  - fromEndpoints:
    - matchLabels:
        org: empire
    toPorts:
    - ports:
      - port: "80"
        protocol: TCP
      rules:
        http:
        - method: "POST"
          path: "/v1/request-landing"
## L7 Layer Network Policy 생성 (위와 동일)
❯ kubectl apply -f https://raw.githubusercontent.com/cilium/cilium/1.17.6/examples/minikube/sw_l3_l4_l7_policy.yaml
ciliumnetworkpolicy.cilium.io/rule1 configured

## Monitoring 
❯ hubble observe -f --pod deathstar --verdict DROPPED

## tiefighter -> deathstar/v1/request-landing (POST Request)
❯ kubectl exec tiefighter -- curl -s -XPOST deathstar.default.svc.cluster.local/v1/request-landing
Ship landed

## tiefighter -> deathstart/v1/exhaust-port (PUT Request)
❯ kubectl exec tiefighter -- curl -s -XPUT deathstar.default.svc.cluster.local/v1/exhaust-port
Access denied

## 모니터링 로그 (API 경로 & HTTP METHOD까지 확인 가능)
Jul 26 06:57:12.949: default/tiefighter:33338 (ID:22234) -> default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) http-request DROPPED (HTTP/1.1 PUT http://deathstar.default.svc.cluster.local/v1/exhaust-port)

❯ kubectl exec xwing -- curl -s -XPOST deathstar.default.svc.cluster.local/v1/request-landing
## ... Timeout

## 모니터링 로그 (계속 DROP)
Jul 26 06:57:33.511: default/xwing:56934 (ID:42250) <> default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) Policy denied DROPPED (TCP Flags: SYN)
Jul 26 06:57:34.526: default/xwing:56934 (ID:42250) <> default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) policy-verdict:none INGRESS DENIED (TCP Flags: SYN)
Jul 26 06:57:34.526: default/xwing:56934 (ID:42250) <> default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) Policy denied DROPPED (TCP Flags: SYN)
Jul 26 06:57:35.550: default/xwing:56934 (ID:42250) <> default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) policy-verdict:none INGRESS DENIED (TCP Flags: SYN)
Jul 26 06:57:35.550: default/xwing:56934 (ID:42250) <> default/deathstar-8c4c77fb7-vhj8x:80 (ID:27476) Policy denied DROPPED (TCP Flags: SYN)
...

## 정책 확인
❯ kubectl describe ciliumnetworkpolicies
Name:         rule1
Namespace:    default
Labels:       <none>
Annotations:  <none>
API Version:  cilium.io/v2
Kind:         CiliumNetworkPolicy
Metadata:
  Creation Timestamp:  2025-07-26T04:49:46Z
  Generation:          2
  Resource Version:    51872136
  UID:                 f4bf08f4-dd1b-4994-9490-579384037a74
Spec:
  Description:  L7 policy to restrict access to specific HTTP call
  Endpoint Selector:
    Match Labels:
      Class:  deathstar
      Org:    empire
  Ingress:
    From Endpoints:
      Match Labels:
        Org:  empire
    To Ports:
      Ports:
        Port:      80
        Protocol:  TCP
      Rules:
        Http:
          Method:  POST
          Path:    /v1/request-landing
Status:
  Conditions:
    Last Transition Time:  2025-07-26T04:49:46Z
    Message:               Policy validation succeeded
    Status:                True
    Type:                  Valid
Events:                    <none>

# cilium CLI로 확인 (cilium-dbg)
kubectl -n kube-system exec <cilium-pod> -- cilium-dbg policy get

L7 Layer Hubble Dropped

7. 삭제

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❯ kubectl delete -f https://raw.githubusercontent.com/cilium/cilium/1.17.6/examples/minikube/http-sw-app.yaml
service "deathstar" deleted
deployment.apps "deathstar" deleted
pod "tiefighter" deleted
pod "xwing" deleted

❯ kubectl delete cnp rule1
ciliumnetworkpolicy.cilium.io "rule1" deleted

8. 마무리

  • L3/L4 정책은 IP, 포트, 프로토콜 수준만 제어합니다. L7 정책을 통해 HTTP 메서드와 경로까지 제한할 수 있습니다.
  • 최소 권한 원칙을 적용하려면 서비스가 실제로 사용하는 엔드포인트만 허용해야 합니다.
  • Cilium은 stateful connection tracking을 수행하므로 응답 패킷은 자동 허용됩니다.
  • kubectl describe, cilium-dbg policy get, cilium-dbg monitor, hubble observe –verdict drop –http 등의 도구를 조합해 정책 적용 여부를 검증합니다.

9. Reference

궁금하신 점이나 추가해야 할 부분은 댓글이나 아래의 링크를 통해 문의해주세요.
Written with KKamJi

Kubernetes, Cilium
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This post is licensed under CC BY 4.0 by the author.