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Debug Traefik Ingress Controller

Chains of iptables used by Kubernetes

Several chains of iptables are programed to do all kinds of filtering and NAT between pods and services when a Service or Endpoint object is created.

  • KUBE-SERVICES is the entry point for service packets. What it does is to match the destination IP:port and dispatch the packet to the corresponding KUBE-SVC-* chain.
  • KUBE-SVC-* acts as a load balancer, which distributes the packet to KUBE-SEP-* chain. The number of KUBE-SEP-* is equal to the number of endpoints behind the service. Which KUBE-SEP-* to be chosen is determined randomly.
  • KUBE-SEP-* represents a Service EndPoint. It simply does DNAT, replacing service IP:port with pod’s endpoint IP:Port.
  • See: https://serenafeng.github.io/2020/03/26/kube-proxy-in-iptables-mode/

Traefik Status

  • Traefik loadbalancer sould be already configured  for following ports:
    • 8087 -> keycloak Service
    • 80 -> HTTP access
    • 443 -> HTTPS access
    • 8080 -> Traefik Admin port
  • The loadbalancer should route any traefik packages to the traefik loadbalancer running on ip 10.43.99.34
  • The svclb-traefik_XXX pods  are runnng an iptables command to trigger this routing
  • The svclb-traefik_XXX pods are runing on each cluster node
  • Each svclb-traefik_XXX pod runs  4 containers  [ lb-port-80, lb-port-443, lb-port-8080, lb-port-8087 ]
  • Traefik pod is listening on pod 8087
# kubectl get pod -n  traefik-ns  -o wide
NAME                       READY   STATUS    RESTARTS   AGE   IP            NODE           NOMINATED NODE   READINESS GATES
svclb-traefik-8rl5h        4/4     Running   0          23h   10.42.0.163   kube-master    <none>           <none>
svclb-traefik-nds69        4/4     Running   0          23h   10.42.2.246   kube-worker2   <none>           <none>
traefik-59cfdc49c7-dmm58   1/1     Running   0          23h   10.42.2.245   kube-worker2   <none>           <none>
svclb-traefik-mk54q        4/4     Running   0          23h   10.42.1.31    kube-worker1   <none>           <none>

# kubectl get svc  -n  traefik-ns  -o wide
NAME      TYPE           CLUSTER-IP    EXTERNAL-IP                                    PORT(S)                                                    AGE   SELECTOR
traefik   LoadBalancer   10.43.99.34   141.75.148.138,141.75.148.139,141.75.148.140   80:31898/TCP,8080:32676/TCP,8087:30158/TCP,443:31879/TCP   27h   app=traefik

# kubectl get endpoints -n  traefik-ns  -o wide
NAME      ENDPOINTS                                                     AGE
traefik   10.42.2.245:80,10.42.2.245:8087,10.42.2.245:443 + 1 more...   27h

Validate Traefik Pod status
# kubectl exec --stdin --tty traefik-59cfdc49c7-dmm58 -n traefik-ns sh
kubectl exec [POD] [COMMAND] is DEPRECATED and will be removed in a future version. Use kubectl exec [POD] -- [COMMAND] instead.

/ # netstat -tulpen  |  egrep '8087 |State'
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 :::8087                 :::*                    LISTEN      1/traefik

Package routing via iptables to traefik IP:Port

  • URL: kube-master.informatik.fh-nuernberg.de:8087
  • iptables routing to keycloak pod running kubeworker2 wiht IP:Port: 10.42.2.245:8087
root@kube-master:/home/master#  iptables -t nat -L KUBE-SERVICES -n  | column -t |  egrep 'KUBE-SERVICES|traefik'
Chain                      KUBE-SERVICES  (2   references)
KUBE-MARK-MASQ             tcp            --   !10.42.0.0/16  10.43.99.34     /*  traefik-ns/traefik:admin                                                      cluster       IP          */     tcp   dpt:8080
KUBE-SVC-2NGTPF5PU2OO4NFC  tcp            --   0.0.0.0/0      10.43.99.34     /*  traefik-ns/traefik:admin                                                      cluster       IP          */     tcp   dpt:8080
KUBE-FW-2NGTPF5PU2OO4NFC   tcp            --   0.0.0.0/0      141.75.148.138  /*  traefik-ns/traefik:admin                                                      loadbalancer  IP          */     tcp   dpt:8080
KUBE-FW-2NGTPF5PU2OO4NFC   tcp            --   0.0.0.0/0      141.75.148.139  /*  traefik-ns/traefik:admin                                                      loadbalancer  IP          */     tcp   dpt:8080
KUBE-FW-2NGTPF5PU2OO4NFC   tcp            --   0.0.0.0/0      141.75.148.140  /*  traefik-ns/traefik:admin                                                      loadbalancer  IP          */     tcp   dpt:8080
KUBE-MARK-MASQ             tcp            --   !10.42.0.0/16  10.43.99.34     /*  traefik-ns/traefik:websecure                                                  cluster       IP          */     tcp   dpt:443
KUBE-SVC-CATTP5HEIU3VUDDR  tcp            --   0.0.0.0/0      10.43.99.34     /*  traefik-ns/traefik:websecure                                                  cluster       IP          */     tcp   dpt:443
KUBE-FW-CATTP5HEIU3VUDDR   tcp            --   0.0.0.0/0      141.75.148.138  /*  traefik-ns/traefik:websecure                                                  loadbalancer  IP          */     tcp   dpt:443
KUBE-FW-CATTP5HEIU3VUDDR   tcp            --   0.0.0.0/0      141.75.148.139  /*  traefik-ns/traefik:websecure                                                  loadbalancer  IP          */     tcp   dpt:443
KUBE-FW-CATTP5HEIU3VUDDR   tcp            --   0.0.0.0/0      141.75.148.140  /*  traefik-ns/traefik:websecure                                                  loadbalancer  IP          */     tcp   dpt:443
KUBE-MARK-MASQ             tcp            --   !10.42.0.0/16  10.43.99.34     /*  traefik-ns/traefik:web                                                        cluster       IP          */     tcp   dpt:80
KUBE-SVC-6R2DDDBNAG6WBID2  tcp            --   0.0.0.0/0      10.43.99.34     /*  traefik-ns/traefik:web                                                        cluster       IP          */     tcp   dpt:80
KUBE-FW-6R2DDDBNAG6WBID2   tcp            --   0.0.0.0/0      141.75.148.138  /*  traefik-ns/traefik:web                                                        loadbalancer  IP          */     tcp   dpt:80
KUBE-FW-6R2DDDBNAG6WBID2   tcp            --   0.0.0.0/0      141.75.148.139  /*  traefik-ns/traefik:web                                                        loadbalancer  IP          */     tcp   dpt:80
KUBE-FW-6R2DDDBNAG6WBID2   tcp            --   0.0.0.0/0      141.75.148.140  /*  traefik-ns/traefik:web                                                        loadbalancer  IP          */     tcp   dpt:80
KUBE-MARK-MASQ             tcp            --   !10.42.0.0/16  10.43.99.34     /*  traefik-ns/traefik:keycloak                                                   cluster       IP          */     tcp   dpt:8087
KUBE-SVC-O2EOQBSIC5NZRIQN  tcp            --   0.0.0.0/0      10.43.99.34     /*  traefik-ns/traefik:keycloak                                                   cluster       IP          */     tcp   dpt:8087
KUBE-FW-O2EOQBSIC5NZRIQN   tcp            --   0.0.0.0/0      141.75.148.138  /*  traefik-ns/traefik:keycloak                                                   loadbalancer  IP          */     tcp   dpt:8087
KUBE-FW-O2EOQBSIC5NZRIQN   tcp            --   0.0.0.0/0      141.75.148.139  /*  traefik-ns/traefik:keycloak                                                   loadbalancer  IP          */     tcp   dpt:8087
KUBE-FW-O2EOQBSIC5NZRIQN   tcp            --   0.0.0.0/0      141.75.148.140  /*  traefik-ns/traefik:keycloak                                                   loadbalancer  IP          */     tcp   dpt:8087

root@kube-master:/home/master# iptables  -v -t nat -L  KUBE-SVC-O2EOQBSIC5NZRIQN  -n  | column -t
Chain  KUBE-SVC-O2EOQBSIC5NZRIQN  (5                         references)
pkts   bytes                      target                     prot         opt  in  out  source     destination
1      60                         KUBE-SEP-AFDBSPUPSG7DXKN6  all          --   *   *    0.0.0.0/0  0.0.0.0/0    /*  traefik-ns/traefik:keycloak  */

root@kube-master:/home/master#  iptables  -v -t nat -L  KUBE-SEP-AFDBSPUPSG7DXKN6   -n  | column -t
Chain  KUBE-SEP-AFDBSPUPSG7DXKN6  (1              references)
pkts   bytes                      target          prot         opt  in  out  source       destination
0      0                          KUBE-MARK-MASQ  all          --   *   *    10.42.2.245  0.0.0.0/0    /*  traefik-ns/traefik:keycloak  */
1      60                         DNAT            tcp          --   *   *    0.0.0.0/0    0.0.0.0/0    /*  traefik-ns/traefik:keycloak  */  tcp  to:10.42.2.245:8087

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