I created a K8s cluster of 5 VMs (1 master and 4 slaves running Ubuntu 16.04.3 LTS) using kubeadm. I used flannel to set up networking in the cluster. I was able to successfully deploy an application. I, then, exposed it via NodePort service. From here things got complicated for me.

Before I started, I disabled the default firewalld service on master and the nodes.

As I understand from the K8s Services doc, the type NodePort exposes the service on all nodes in the cluster. However, when I created it, the service was exposed only on 2 nodes out of 4 in the cluster. I am guessing that's not the expected behavior (right?)

For troubleshooting, here are some resource specs:

root@vm-vivekse-003:~# kubectl get nodes
NAME              STATUS    AGE       VERSION
vm-deepejai-00b   Ready     5m        v1.7.3
vm-plashkar-006   Ready     4d        v1.7.3
vm-rosnthom-00f   Ready     4d        v1.7.3
vm-vivekse-003    Ready     4d        v1.7.3   //the master
vm-vivekse-004    Ready     16h       v1.7.3

root@vm-vivekse-003:~# kubectl get pods -o wide -n playground
NAME                                     READY     STATUS    RESTARTS   AGE       IP           NODE
kubernetes-bootcamp-2457653786-9qk80     1/1       Running   0          2d        10.244.3.6   vm-rosnthom-00f
springboot-helloworld-2842952983-rw0gc   1/1       Running   0          1d        10.244.3.7   vm-rosnthom-00f

root@vm-vivekse-003:~# kubectl get svc -o wide -n playground
NAME        CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE       SELECTOR
sb-hw-svc   10.101.180.19   <nodes>       9000:30847/TCP   5h        run=springboot-helloworld

root@vm-vivekse-003:~# kubectl describe svc sb-hw-svc -n playground
Name:               sb-hw-svc
Namespace:          playground
Labels:             <none>
Annotations:        <none>
Selector:           run=springboot-helloworld
Type:               NodePort
IP:                 10.101.180.19
Port:               <unset>   9000/TCP
NodePort:           <unset>   30847/TCP
Endpoints:          10.244.3.7:9000
Session Affinity:   None
Events:             <none>

root@vm-vivekse-003:~# kubectl get endpoints sb-hw-svc -n playground -o yaml
apiVersion: v1
kind: Endpoints
metadata:
  creationTimestamp: 2017-08-09T06:28:06Z
  name: sb-hw-svc
  namespace: playground
  resourceVersion: "588958"
  selfLink: /api/v1/namespaces/playground/endpoints/sb-hw-svc
  uid: e76d9cc1-7ccb-11e7-bc6a-fa163efaba6b
subsets:
- addresses:
  - ip: 10.244.3.7
    nodeName: vm-rosnthom-00f
    targetRef:
      kind: Pod
      name: springboot-helloworld-2842952983-rw0gc
      namespace: playground
      resourceVersion: "473859"
      uid: 16d9db68-7c1a-11e7-bc6a-fa163efaba6b
  ports:
  - port: 9000
    protocol: TCP

After some tinkering I realized that on those 2 "faulty" nodes, those services were not available from within those hosts itself.

Node01 (working):

root@vm-vivekse-004:~# curl 127.0.0.1:30847      //<localhost>:<nodeport>
Hello Docker World!!
root@vm-vivekse-004:~# curl 10.101.180.19:9000   //<cluster-ip>:<port>
Hello Docker World!!
root@vm-vivekse-004:~# curl 10.244.3.7:9000      //<pod-ip>:<port>
Hello Docker World!!

Node02 (working):

root@vm-rosnthom-00f:~# curl 127.0.0.1:30847
Hello Docker World!!
root@vm-rosnthom-00f:~# curl 10.101.180.19:9000
Hello Docker World!!
root@vm-rosnthom-00f:~# curl 10.244.3.7:9000
Hello Docker World!!

Node03 (not working):

root@vm-plashkar-006:~# curl 127.0.0.1:30847
curl: (7) Failed to connect to 127.0.0.1 port 30847: Connection timed out
root@vm-plashkar-006:~# curl 10.101.180.19:9000
curl: (7) Failed to connect to 10.101.180.19 port 9000: Connection timed out
root@vm-plashkar-006:~# curl 10.244.3.7:9000
curl: (7) Failed to connect to 10.244.3.7 port 9000: Connection timed out

Node04 (not working):

root@vm-deepejai-00b:/# curl 127.0.0.1:30847
curl: (7) Failed to connect to 127.0.0.1 port 30847: Connection timed out
root@vm-deepejai-00b:/# curl 10.101.180.19:9000
curl: (7) Failed to connect to 10.101.180.19 port 9000: Connection timed out
root@vm-deepejai-00b:/# curl 10.244.3.7:9000
curl: (7) Failed to connect to 10.244.3.7 port 9000: Connection timed out

Tried netstat and telnet on all 4 slaves. Here's the output:

Node01 (the working host):

root@vm-vivekse-004:~# netstat -tulpn | grep 30847
tcp6       0      0 :::30847                :::*                    LISTEN      27808/kube-proxy
root@vm-vivekse-004:~# telnet 127.0.0.1 30847
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.

Node02 (the working host):

root@vm-rosnthom-00f:~# netstat -tulpn | grep 30847
tcp6       0      0 :::30847                :::*                    LISTEN      11842/kube-proxy
root@vm-rosnthom-00f:~# telnet 127.0.0.1 30847
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.

Node03 (the not-working host):

root@vm-plashkar-006:~# netstat -tulpn | grep 30847
tcp6       0      0 :::30847                :::*                    LISTEN      7791/kube-proxy
root@vm-plashkar-006:~# telnet 127.0.0.1 30847
Trying 127.0.0.1...
telnet: Unable to connect to remote host: Connection timed out

Node04 (the not-working host):

root@vm-deepejai-00b:/# netstat -tulpn | grep 30847
tcp6       0      0 :::30847                :::*                    LISTEN      689/kube-proxy
root@vm-deepejai-00b:/# telnet 127.0.0.1 30847
Trying 127.0.0.1...
telnet: Unable to connect to remote host: Connection timed out

Addition info:

From the kubectl get pods output, I can see that the pod is actually deployed on slave vm-rosnthom-00f. I am able to ping this host from all the 5 VMs and curl vm-rosnthom-00f:30847 also works from all the VMs.

I can clearly see that the internal cluster networking is messed up, but I am unsure how to resolve it! iptables -L for all the slaves are identical, and even the Local Loopback (ifconfig lo) is up and running for all the slaves. I'm completely clueless as to how to fix it!