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Created November 22, 2018 10:36
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kubernetes kube-dns components, debugging
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Kube-dns.md

Summary

  • dnsmasq front ends the requests and sends them on to kube-dns

    dnsmasq
  --cache-size=1000
  --no-resolv
  --server=127.0.0.1#10053
  --log-facility=-

  • kube-dns handles the cluster level requests

      kube-dns 
  --domain=cluster.local
  --dns-port=10053
  --config-map=kube-dns
  --v=2

  • who handles the internet lookups?

Note: Looks like all requests are handled by kube-dns even the ones external to the cluster

" The running Kubernetes DNS pod holds 3 containers - kubedns, dnsmasq and a health check called healthz. The kubedns process watches the Kubernetes master for changes in Services and Endpoints, and maintains in-memory lookup structures to service DNS requests. The dnsmasq container adds DNS caching to improve performance. The healthz container provides a single health check endpoint while performing dual healthchecks (for dnsmasq and kubedns). "

  • iptables are used to send traffic from the POD to the kube-dns POD

What is the IP the DNS server

It has a cluster level IP

root@singlevm:~# kubectl get svc --namespace=kube-system
NAME       CLUSTER-IP   EXTERNAL-IP   PORT(S)         AGE
kube-dns   10.96.0.10   <none>        53/UDP,53/TCP   22h

Backed up by one or more PODS with internal IPs

root@singlevm:~# kubectl get ep kube-dns --namespace=kube-system
NAME       ENDPOINTS                     AGE
kube-dns   10.244.0.2:53,10.244.0.2:53   22h

And the Cluster Level IP is placed in the container resolver

/ # cat /etc/resolv.conf
search default.svc.cluster.local svc.cluster.local cluster.local
nameserver 10.96.0.10
options ndots:5

Open: Why do we see a query go out with just nginx even when ndots is set to 5?

How is DNS traffic sent from POD to kube-dns via Cluster Level IP

SNAT and DNAT Rules to send traffic from Service IP to POD

-A KUBE-SERVICES -d 10.96.0.10/32 -p udp -m comment --comment "kube-system/kube-dns:dns cluster IP" -m udp --dport 53 -j KUBE-SVC-TCOU7JCQXEZGVUNU
-A KUBE-SVC-TCOU7JCQXEZGVUNU -m comment --comment "kube-system/kube-dns:dns" -j KUBE-SEP-YIL6JZP7A3QYXJU2
-A KUBE-SEP-YIL6JZP7A3QYXJU2 -s 10.244.0.2/32 -m comment --comment "kube-system/kube-dns:dns" -j KUBE-MARK-MASQ
-A KUBE-SEP-YIL6JZP7A3QYXJU2 -p udp -m comment --comment "kube-system/kube-dns:dns" -m udp -j DNAT --to-destination 10.244.0.2:53

-A KUBE-SERVICES -d 10.96.0.10/32 -p tcp -m comment --comment "kube-system/kube-dns:dns-tcp cluster IP" -m tcp --dport 53 -j KUBE-SVC-ERIFXISQEP7F7OF4
-A KUBE-SVC-ERIFXISQEP7F7OF4 -m comment --comment "kube-system/kube-dns:dns-tcp" -j KUBE-SEP-IT2ZTR26TO4XFPTO
-A KUBE-SEP-IT2ZTR26TO4XFPTO -s 10.244.0.2/32 -m comment --comment "kube-system/kube-dns:dns-tcp" -j KUBE-MARK-MASQ
-A KUBE-SEP-IT2ZTR26TO4XFPTO -p tcp -m comment --comment "kube-system/kube-dns:dns-tcp" -m tcp -j DNAT --to-destination 10.244.0.2:53


-A KUBE-MARK-MASQ -j MARK --set-xmark 0x4000/0x4000
-A KUBE-POSTROUTING -m comment --comment "kubernetes service traffic requiring SNAT" -m mark --mark 0x4000/0x4000 -j MASQUERADE

What is in the kube-dns POD

root@singlevm:/var/run/docker/netns# kubectl describe pod --namespace=kube-system kube-dns-2924299975-fpplx
Name:           kube-dns-2924299975-fpplx
Namespace:      kube-system
Node:           singlevm/10.0.2.15
Start Time:     Mon, 13 Mar 2017 21:44:20 +0000
Labels:         component=kube-dns
                k8s-app=kube-dns
                kubernetes.io/cluster-service=true
                name=kube-dns
                pod-template-hash=2924299975
                tier=node
Status:         Running
IP:             10.244.0.2
Controllers:    ReplicaSet/kube-dns-2924299975
Containers:
  kube-dns:
    Container ID:       docker://6e587bf9493a0b31ce49cee749b12259a320ab403ba4c9665a558e0152101a05
    Image:              gcr.io/google_containers/kubedns-amd64:1.9
    Image ID:           docker-pullable://gcr.io/google_containers/kubedns-amd64@sha256:3d3d67f519300af646e00adcf860b2f380d35ed4364e550d74002dadace20ead
    Ports:              10053/UDP, 10053/TCP, 10055/TCP
    Args:
      --domain=cluster.local
      --dns-port=10053
      --config-map=kube-dns
      --v=2
    Limits:
      memory:   170Mi
    Requests:
      cpu:              100m
      memory:           70Mi
    State:              Running
      Started:          Mon, 13 Mar 2017 21:44:48 +0000
    Ready:              True
    Restart Count:      0
    Liveness:           http-get http://:8080/healthz-kubedns delay=60s timeout=5s period=10s #success=1 #failure=5
    Readiness:          http-get http://:8081/readiness delay=3s timeout=5s period=10s #success=1 #failure=3
    Volume Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-cbd28 (ro)
    Environment Variables:
      PROMETHEUS_PORT:  10055
  dnsmasq:
    Container ID:       docker://aca586acbbbd2e0ef915da3f2d7afb591aecec97b92129124fdc26ea260d5c3a
    Image:              gcr.io/google_containers/kube-dnsmasq-amd64:1.4
    Image ID:           docker-pullable://gcr.io/google_containers/kube-dnsmasq-amd64@sha256:a722df15c0cf87779aad8ba2468cf072dd208cb5d7cfcaedd90e66b3da9ea9d2
    Ports:              53/UDP, 53/TCP
    Args:
      --cache-size=1000
      --no-resolv
      --server=127.0.0.1#10053
      --log-facility=-
    Requests:
      cpu:              150m
      memory:           10Mi
    State:              Running
      Started:          Mon, 13 Mar 2017 21:44:53 +0000
    Ready:              True
    Restart Count:      0
    Liveness:           http-get http://:8080/healthz-dnsmasq delay=60s timeout=5s period=10s #success=1 #failure=5
    Volume Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-cbd28 (ro)
    Environment Variables:      <none>
  dnsmasq-metrics:
    Container ID:       docker://6217a6e224507a648506097f49d9913d9d26edd3f12b88644e012705d7d7be7f
    Image:              gcr.io/google_containers/dnsmasq-metrics-amd64:1.0
    Image ID:           docker-pullable://gcr.io/google_containers/dnsmasq-metrics-amd64@sha256:4063e37fd9b2fd91b7cc5392ed32b30b9c8162c4c7ad2787624306fc133e80a9
    Port:               10054/TCP
    Args:
      --v=2
      --logtostderr
    Requests:
      memory:           10Mi
    State:              Running
      Started:          Mon, 13 Mar 2017 21:44:58 +0000
    Ready:              True
    Restart Count:      0
    Liveness:           http-get http://:10054/metrics delay=60s timeout=5s period=10s #success=1 #failure=5
    Volume Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-cbd28 (ro)
    Environment Variables:      <none>
  healthz:
    Container ID:       docker://9089753b3461b9226cd6dd82e2043d47f2333580b22306490432657ca972b531
    Image:              gcr.io/google_containers/exechealthz-amd64:1.2
    Image ID:           docker-pullable://gcr.io/google_containers/exechealthz-amd64@sha256:503e158c3f65ed7399f54010571c7c977ade7fe59010695f48d9650d83488c0a
    Port:               8080/TCP
    Args:
      --cmd=nslookup kubernetes.default.svc.cluster.local 127.0.0.1 >/dev/null
      --url=/healthz-dnsmasq
      --cmd=nslookup kubernetes.default.svc.cluster.local 127.0.0.1:10053 >/dev/null
      --url=/healthz-kubedns
      --port=8080
      --quiet
    Limits:
      memory:   50Mi
    Requests:
      cpu:              10m
      memory:           50Mi
    State:              Running
      Started:          Mon, 13 Mar 2017 21:45:02 +0000
    Ready:              True
    Restart Count:      0
    Volume Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-cbd28 (ro)
    Environment Variables:      <none>
Conditions:
  Type          Status
  Initialized   True
  Ready         True
  PodScheduled  True
Volumes:
  default-token-cbd28:
    Type:       Secret (a volume populated by a Secret)
    SecretName: default-token-cbd28
QoS Class:      Burstable
Tolerations:    dedicated=master:NoSchedule
No events.

Who/What is listening in the kube-dns namespace

Kube-dns internal IP

root@singlevm:/var/run/docker/netns# nsenter --net=25cb799cd23e
root@singlevm:/var/run/docker/netns# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
3: eth0@if6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UP group default
    link/ether 0a:58:0a:f4:00:02 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 10.244.0.2/24 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::d4f9:8bff:fe0b:c4e5/64 scope link tentative dadfailed
       valid_lft forever preferred_lft forever

DNS Server Related Sockets

root@singlevm:/var/run/docker/netns# netstat -plunt
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 0.0.0.0:53              0.0.0.0:*               LISTEN      26773/dnsmasq
tcp6       0      0 :::10053                :::*                    LISTEN      26336/kube-dns
tcp6       0      0 :::10054                :::*                    LISTEN      27307/dnsmasq-metri
tcp6       0      0 :::10055                :::*                    LISTEN      26336/kube-dns
tcp6       0      0 :::8080                 :::*                    LISTEN      27516/exechealthz
tcp6       0      0 :::8081                 :::*                    LISTEN      26336/kube-dns
tcp6       0      0 :::53                   :::*                    LISTEN      26773/dnsmasq
udp        0      0 0.0.0.0:53              0.0.0.0:*                           26773/dnsmasq
udp6       0      0 :::10053                :::*                                26336/kube-dns
udp6       0      0 :::53                   :::*                                26773/dnsmasq

Connection to API Server/etcd??

root@singlevm:/var/run/docker/netns# netstat -a
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 *:domain                *:*                     LISTEN
tcp        0      0 10.244.0.2:57658        10.96.0.1:https         ESTABLISHED

What is the POD IP (internal)

root@singlevm:/var/run/docker/netns# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
3: eth0@if6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UP group default
    link/ether 0a:58:0a:f4:00:02 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 10.244.0.2/24 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::d4f9:8bff:fe0b:c4e5/64 scope link tentative dadfailed
       valid_lft forever preferred_lft forever

How are the PODs setup for DNS

kubectl run -i -t netdebug --image=mcastelino/nettools --restart=Never 
#kubectl run -i -t busybox --image=busybox --restart=Never
#Busybox libc has an issue with ndots which results in incorrect lookup sequences.

/ # cat /etc/resolv.conf
search default.svc.cluster.local svc.cluster.local cluster.local
nameserver 10.96.0.10
options ndots:5
/ # cat /etc/resolv.conf
search default.svc.cluster.local svc.cluster.local cluster.local
nameserver 10.96.0.10
options ndots:5
/ # ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
3: eth0@if12: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1450 qdisc noqueue
    link/ether 0a:58:0a:f4:00:08 brd ff:ff:ff:ff:ff:ff
    inet 10.244.0.8/24 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::b0e8:adff:fef8:5522/64 scope link tentative flags 08
       valid_lft forever preferred_lft forever
/ # nslookup nginx
Server:    10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local

Name:      nginx
Address 1: 10.109.102.230 nginx.default.svc.cluster.local

How is the service exposed

root@singlevm:/var/run/docker/netns# kubectl get svc
NAME         CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE
kubernetes   10.96.0.1        <none>        443/TCP        20h
nginx        10.109.102.230   <nodes>       80:30361/TCP   18h

Resolution within the dns POD

23:04:02.789492 IP (tos 0x0, ttl 64, id 7088, offset 0, flags [none], proto UDP (17), length 77)
    10.244.0.20.35926 > 10.244.0.2.domain: 44017+ A? nginx.default.svc.cluster.local. (49)
23:04:02.789602 IP (tos 0x0, ttl 64, id 19401, offset 0, flags [DF], proto UDP (17), length 93)
    10.244.0.2.domain > 10.244.0.20.35926: 44017 1/0/0 nginx.default.svc.cluster.local. A 10.109.102.230 (65)
23:04:02.789699 IP (tos 0x0, ttl 64, id 48377, offset 0, flags [DF], proto UDP (17), length 70)
    10.244.0.2.33618 > 10.0.2.3.domain: 9825+ PTR? 20.0.244.10.in-addr.arpa. (42)
23:04:02.790694 IP (tos 0x0, ttl 63, id 19024, offset 0, flags [none], proto UDP (17), length 164)
    10.0.2.3.domain > 10.244.0.2.33618: 9825 NXDomain* 0/1/0 (136)

Host side iptables for a kubernetes node

# Generated by iptables-save v1.6.0 on Tue Mar 14 18:29:49 2017
*nat
:PREROUTING ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:OUTPUT ACCEPT [12:720]
:POSTROUTING ACCEPT [12:720]
:DOCKER - [0:0]
:KUBE-MARK-DROP - [0:0]
:KUBE-MARK-MASQ - [0:0]
:KUBE-NODEPORTS - [0:0]
:KUBE-POSTROUTING - [0:0]
:KUBE-SEP-263UWIYWZXPNMPMF - [0:0]
:KUBE-SEP-ECWJ4XMO64PCJIJZ - [0:0]
:KUBE-SEP-EYCY2JIROCGGPBZO - [0:0]
:KUBE-SEP-IT2ZTR26TO4XFPTO - [0:0]
:KUBE-SEP-OGNOLD2JUSLFPOMZ - [0:0]
:KUBE-SEP-YIL6JZP7A3QYXJU2 - [0:0]
:KUBE-SERVICES - [0:0]
:KUBE-SVC-4N57TFCL4MD7ZTDA - [0:0]
:KUBE-SVC-ERIFXISQEP7F7OF4 - [0:0]
:KUBE-SVC-NPX46M4PTMTKRN6Y - [0:0]
:KUBE-SVC-TCOU7JCQXEZGVUNU - [0:0]
-A PREROUTING -m comment --comment "kubernetes service portals" -j KUBE-SERVICES
-A PREROUTING -m addrtype --dst-type LOCAL -j DOCKER
-A OUTPUT -m comment --comment "kubernetes service portals" -j KUBE-SERVICES
-A OUTPUT ! -d 127.0.0.0/8 -m addrtype --dst-type LOCAL -j DOCKER
-A POSTROUTING -m comment --comment "kubernetes postrouting rules" -j KUBE-POSTROUTING
-A POSTROUTING -s 172.17.0.0/16 ! -o docker0 -j MASQUERADE
-A POSTROUTING -s 10.244.0.0/16 -d 10.244.0.0/16 -j RETURN
-A POSTROUTING -s 10.244.0.0/16 ! -d 224.0.0.0/4 -j MASQUERADE
-A POSTROUTING ! -s 10.244.0.0/16 -d 10.244.0.0/16 -j MASQUERADE
-A DOCKER -i docker0 -j RETURN
-A KUBE-MARK-DROP -j MARK --set-xmark 0x8000/0x8000
-A KUBE-MARK-MASQ -j MARK --set-xmark 0x4000/0x4000
-A KUBE-NODEPORTS -p tcp -m comment --comment "default/nginx:" -m tcp --dport 30361 -j KUBE-MARK-MASQ
-A KUBE-NODEPORTS -p tcp -m comment --comment "default/nginx:" -m tcp --dport 30361 -j KUBE-SVC-4N57TFCL4MD7ZTDA
-A KUBE-POSTROUTING -m comment --comment "kubernetes service traffic requiring SNAT" -m mark --mark 0x4000/0x4000 -j MASQUERADE
-A KUBE-SEP-263UWIYWZXPNMPMF -s 10.244.0.4/32 -m comment --comment "default/nginx:" -j KUBE-MARK-MASQ
-A KUBE-SEP-263UWIYWZXPNMPMF -p tcp -m comment --comment "default/nginx:" -m tcp -j DNAT --to-destination 10.244.0.4:80
-A KUBE-SEP-ECWJ4XMO64PCJIJZ -s 10.244.0.3/32 -m comment --comment "default/nginx:" -j KUBE-MARK-MASQ
-A KUBE-SEP-ECWJ4XMO64PCJIJZ -p tcp -m comment --comment "default/nginx:" -m tcp -j DNAT --to-destination 10.244.0.3:80
-A KUBE-SEP-EYCY2JIROCGGPBZO -s 10.244.0.5/32 -m comment --comment "default/nginx:" -j KUBE-MARK-MASQ
-A KUBE-SEP-EYCY2JIROCGGPBZO -p tcp -m comment --comment "default/nginx:" -m tcp -j DNAT --to-destination 10.244.0.5:80
-A KUBE-SEP-IT2ZTR26TO4XFPTO -s 10.244.0.2/32 -m comment --comment "kube-system/kube-dns:dns-tcp" -j KUBE-MARK-MASQ
-A KUBE-SEP-IT2ZTR26TO4XFPTO -p tcp -m comment --comment "kube-system/kube-dns:dns-tcp" -m tcp -j DNAT --to-destination 10.244.0.2:53
-A KUBE-SEP-OGNOLD2JUSLFPOMZ -s 10.0.2.15/32 -m comment --comment "default/kubernetes:https" -j KUBE-MARK-MASQ
-A KUBE-SEP-OGNOLD2JUSLFPOMZ -p tcp -m comment --comment "default/kubernetes:https" -m recent --set --name KUBE-SEP-OGNOLD2JUSLFPOMZ --mask 255.255.255.255 --rsource -m tcp -j DNAT --to-destination 10.0.2.15:6443
-A KUBE-SEP-YIL6JZP7A3QYXJU2 -s 10.244.0.2/32 -m comment --comment "kube-system/kube-dns:dns" -j KUBE-MARK-MASQ
-A KUBE-SEP-YIL6JZP7A3QYXJU2 -p udp -m comment --comment "kube-system/kube-dns:dns" -m udp -j DNAT --to-destination 10.244.0.2:53
-A KUBE-SERVICES -d 10.96.0.10/32 -p tcp -m comment --comment "kube-system/kube-dns:dns-tcp cluster IP" -m tcp --dport 53 -j KUBE-SVC-ERIFXISQEP7F7OF4
-A KUBE-SERVICES -d 10.109.102.230/32 -p tcp -m comment --comment "default/nginx: cluster IP" -m tcp --dport 80 -j KUBE-SVC-4N57TFCL4MD7ZTDA
-A KUBE-SERVICES -d 10.96.0.1/32 -p tcp -m comment --comment "default/kubernetes:https cluster IP" -m tcp --dport 443 -j KUBE-SVC-NPX46M4PTMTKRN6Y
-A KUBE-SERVICES -d 10.96.0.10/32 -p udp -m comment --comment "kube-system/kube-dns:dns cluster IP" -m udp --dport 53 -j KUBE-SVC-TCOU7JCQXEZGVUNU
-A KUBE-SERVICES -m comment --comment "kubernetes service nodeports; NOTE: this must be the last rule in this chain" -m addrtype --dst-type LOCAL -j KUBE-NODEPORTS
-A KUBE-SVC-4N57TFCL4MD7ZTDA -m comment --comment "default/nginx:" -m statistic --mode random --probability 0.33332999982 -j KUBE-SEP-ECWJ4XMO64PCJIJZ
-A KUBE-SVC-4N57TFCL4MD7ZTDA -m comment --comment "default/nginx:" -m statistic --mode random --probability 0.50000000000 -j KUBE-SEP-263UWIYWZXPNMPMF
-A KUBE-SVC-4N57TFCL4MD7ZTDA -m comment --comment "default/nginx:" -j KUBE-SEP-EYCY2JIROCGGPBZO
-A KUBE-SVC-ERIFXISQEP7F7OF4 -m comment --comment "kube-system/kube-dns:dns-tcp" -j KUBE-SEP-IT2ZTR26TO4XFPTO
-A KUBE-SVC-NPX46M4PTMTKRN6Y -m comment --comment "default/kubernetes:https" -m recent --rcheck --seconds 10800 --reap --name KUBE-SEP-OGNOLD2JUSLFPOMZ --mask 255.255.255.255 --rsource -j KUBE-SEP-OGNOLD2JUSLFPOMZ
-A KUBE-SVC-NPX46M4PTMTKRN6Y -m comment --comment "default/kubernetes:https" -j KUBE-SEP-OGNOLD2JUSLFPOMZ
-A KUBE-SVC-TCOU7JCQXEZGVUNU -m comment --comment "kube-system/kube-dns:dns" -j KUBE-SEP-YIL6JZP7A3QYXJU2
COMMIT
# Completed on Tue Mar 14 18:29:49 2017
# Generated by iptables-save v1.6.0 on Tue Mar 14 18:29:49 2017
*filter
:INPUT ACCEPT [1504:637060]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [1482:657015]
:DOCKER - [0:0]
:DOCKER-ISOLATION - [0:0]
:KUBE-FIREWALL - [0:0]
:KUBE-SERVICES - [0:0]
-A INPUT -j KUBE-FIREWALL
-A FORWARD -j DOCKER-ISOLATION
-A FORWARD -o docker0 -j DOCKER
-A FORWARD -o docker0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -i docker0 ! -o docker0 -j ACCEPT
-A FORWARD -i docker0 -o docker0 -j ACCEPT
-A OUTPUT -m comment --comment "kubernetes service portals" -j KUBE-SERVICES
-A OUTPUT -j KUBE-FIREWALL
-A DOCKER-ISOLATION -j RETURN
-A KUBE-FIREWALL -m comment --comment "kubernetes firewall for dropping marked packets" -m mark --mark 0x8000/0x8000 -j DROP
COMMIT
# Completed on Tue Mar 14 18:29:49 2017

Headless Deployments

Expose all the IPs of the underlying service.

kubectl run nginx-headless --image=nginx --port=81 --replicas=3 
kubectl expose deployment nginx-headless --type NodePort --cluster-ip=none

/ # nslookup nginx-headless
Server:    10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local

Name:      nginx-headless
Address 1: 10.244.0.13
Address 2: 10.244.0.14
Address 3: 10.244.0.15
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