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Can't access an Express.js service via a Kubernetes NodePort service in a MicroK8s cluster

11/4/2019

I have a simple Express.js server Dockerized and when I run it like:

docker run -p 3000:3000 mytag:my-build-id

http://localhost:3000/ responds just fine and also if I use the LAN IP of my workstation like http://10.44.103.60:3000/

Now if I deploy this to MicroK8s with a service deployment declaration like:

apiVersion: v1
kind: Service
metadata:
  creationTimestamp: null
  name: my-service
spec:
  type: NodePort
  ports:
  - name: "3000"
    port: 3000
    targetPort: 3000
status:
  loadBalancer: {}

and pod specification like so (update 2019-11-05):

apiVersion: apps/v1
kind: Deployment
metadata:
  creationTimestamp: null
  name: my-service
spec:
  replicas: 1
  selector:
    matchLabels:
      name: my-service
  strategy: {}
  template:
    metadata:
      creationTimestamp: null
      labels:
        name: my-service
    spec:
      containers:
      - image: mytag:my-build-id
        name: my-service
        ports:
        - containerPort: 3000
        resources: {}
      restartPolicy: Always
status: {}

and obtain the exposed NodePort via kubectl get services to be 32750 and try to visit it on the MicroK8s host machine like so:

curl http://127.0.0.1:32750

then the request just hangs and if I try to visit the LAN IP of the MicroK8s host from my workstation at http://192.168.191.248:32750/ then the request is immediately refused.

But, if I try to port forward into the pod with

kubectl port-forward my-service-5db955f57f-q869q 3000:3000

then http://localhost:3000/ works just fine.

So the pod deployment seems to be working fine and example services like the microbot-service work just fine on that cluster.

I've made sure the Express.js server listens on all IPs with

app.listen(port, '0.0.0.0', () =>  ...

So what can be the issue?

-- Bjorn Thor Jonsson

docker

express

kubernetes

microk8s

2 Answers

11/5/2019

You need to add a selector to your service. This will tell Kubernetes how to find your deployment. Additionally you can use nodePort to specify the port number of your service. After doing that you will be able to curl your MicroK8s IP.

Your Service YAML should look like this:

apiVersion: v1
kind: Service
metadata:
  creationTimestamp: null
  name: my-service
spec:
  type: NodePort
  ports:
  - name: http
    port: 80
    targetPort: 80
    nodePort: 30001
  selector: 
    name: my-service      
status:
  loadBalancer: {}

-- mWatney

Source: StackOverflow

11/5/2019

the LAN IP of the MicroK8s host from my workstation

That is the central source of your misunderstanding; localhost, 127.0.0.1, and your machine's LAN IP have nothing to do with what is apparently a virtual machine running microk8s (which it would have been infinitely valuable to actually include that information in your question, rather than us having to deduce it from one buried sentence)

I've made sure the Express.js server listens on all IPs with

Based on what you reported later:

at http://192.168.191.248:32750/ then the request is immediately refused.

then it appears that your express server is not, in fact, listening on all interfaces. That explains why you can successfully port-forward into the Pod (which causes traffic to appear on the Pod's localhost) but not reach it from "outside" the Pod

You can also test that theory by using another Pod inside the cluster to curl its Pod IP on port 3000 (in order to side-step the Service and thus NodePort parts)

There is a small chance that you have misconfigured your Pod and Service relationship, but since you didn't post your PodSpec, and the behavior you are describing sounds a lot more like an express misconfiguration, we'll go with that until we have evidence to the contrary

-- mdaniel

Source: StackOverflow

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Can't access an Express.js service via a Kubernetes NodePort service in a MicroK8s cluster

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