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Chris
Asked: 2019-07-04 06:39:03 +0800 CST

Kubernetes - making Nodeport accessible on all nodes

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I'm running a Kubernetes bare metal install and I'm trying to make my test nginx application (simply created with kubectl create deployment nginx --image=nginx) visible remotely from all nodes. The idea being I can then use a bare metal HAProxy installation to route the traffic appropriately.

From everything I've read this configuration should work and allow access via the port across nodes. Additionally, performing a netstat does seem to show that the nodeport is listening on all nodes - 

user@kube2:~$ netstat -an | grep :30196
tcp6       0      0 :::30196                :::*                    LISTEN

My service.yaml file - 

apiVersion: v1
kind: Service
metadata:
  name: test-svc
  namespace: default
spec:
  type: NodePort
  externalTrafficPolicy: Cluster
  ports:
  - port: 80
    targetPort: 80
    protocol: TCP
    name: http
  - port: 443
    targetPort: 443
    protocol: TCP
    name: https
  selector:
    app: nginx

My node networking configuration - 

kube1 - 192.168.1.130 (master)
kube2 - 192.168.1.131
kube3 - 192.168.1.132

My service running - 

user@kube1:~$ kubectl get svc -o wide
NAME         TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)                      AGE   SELECTOR
kubernetes   ClusterIP   10.96.0.1        <none>        443/TCP                      18m   <none>
test-svc     NodePort    10.103.126.143   <none>        80:30196/TCP,443:32580/TCP   14m   app=nginx

However, despite all the above, my service is only accessible on the node it is running on (kube3/192.168.1.132). Any ideas why this would be or am I just understanding Kubernetes?

I'd had a look at load balancers and ingress but what doesn't make sense is if I routed all traffic to my master to distribute (kube1), what if kube1 went down? Surely I need a load balancer to target my load balancer?!

Hope someone can help!

Thanks, Chris.

kubernetes

3 Answers

  1. If you want to expose service to outside cluster use service type either LoadBalancer or ingree. However is you use LoadBalancer approach has its own limitation. You cannot configure a LoadBalancer to terminate HTTPS traffic, virtual hosts or path-based routing. In Kubernetes 1.2 a separate resource called Ingress is introduced for this purpose. Here is example of LoadBalancer.

    apiVersion: v1
kind: Service
metadata:
  labels:
    app: nginx-app
  name: nginx-svc
  namespace: default
spec:
  type: LoadBalancer  # use LoadBalancer as type here
  ports:
    - port: 80
  selector:
    app: nginx-app

$ kubectl get services -l app=nginx-app -o wide
NAME        TYPE           CLUSTER-IP       EXTERNAL-IP                                                                  PORT(S)        AGE       SELECTOR
nginx-svc   LoadBalancer   <ip>   a54a62300696611e88ba00af02406931-1787163476.myserver.com   80:31196/TCP   9m        app=nginx-app

    Post that test url

    $curl a54a62300696611e88ba00af02406931-1787163476.myserver.com
    • 1

  2. In order to access you local Kubernetes Cluster PODs a NodePort needs to be created. The NodePort will publish your service in every node using using its public IP and a port. Then you can access the service using any of the cluster IPs and the assigned port.

    Defining a NodePort in Kubernetes:

    apiVersion: v1
kind: Service
metadata:
  name: nginx-service-np
  labels:
    name: nginx-service-np
spec:
  type: NodePort
  ports:
    - port: 8082        # Cluster IP, i.e. http://10.103.75.9:8082
      targetPort: 8080  # Application port
      nodePort: 30000   # (EXTERNAL-IP VirtualBox IPs) i.e. http://192.168.50.11:30000/ http://192.168.50.12:30000/ http://192.168.50.13:30000/
      protocol: TCP
      name: http
  selector:
    app: nginx

    See a full example with source code at Building a Kubernetes Cluster with Vagrant and Ansible (without Minikube).

    The nginx ingress controller can be replaced also with Istio if you want to benefit from a service mesh architecture for:

    • Load Balance traffic, external o internal
    • Control failures, retries, routing
    • Apply limits and monitor network traffic between services
    • Secure communication

    See Installing Istio in Kubernetes under VirtualBox (without Minikube).

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  3. Yet another option is to expose Nginx Ingress controller over NodePort (although not recommended for Production clusters). NodePort type still gives you the LoadBalancing capabilities, and to which specific Pod (backing the Service endpoints) the traffic should be sent, you control with 'service.spec.sessionAffinity' and Container Probes.

    If you would have more than 1 replica of nginx Pod in your Deployment spec (example here), you could control pod to node assignment via pod affinity and anti-affinity feature.

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