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I'm trying to stand up a pair of kubernetes workers on EC2 instances, and running into a problem where the service does not appear to "see" all of the pods that it should be able to see.

My exact environment is a pair of AWS Snowballs, Red and Blue, and my cluster looks like control, worker-red, and worker-blue [1]. I'm deploying a dummy python server that waits for a GET on port 8080, and replies with the local hostname. I've set it up with enough replicas that both worker-red and worker-blue have at least one pod each. Finally, I've created a service, the spec of which looks like

spec:
    type: NodePort
    selector:
        app: hello-server
    ports:
        - port: 8080
          targetPort: 8080
          nodePort: 30080

I can now check that my pods are up

kubectl get pods -o wide
NAME                                      READY   STATUS    RESTARTS   AGE   IP              NODE          NOMINATED NODE   READINESS GATES
hello-world-deployment-587468bdb7-hf4dq   1/1     Running   0          27m   192.168.1.116   worker.red    <none>           <none>
hello-world-deployment-587468bdb7-mclhm   1/1     Running   0          27m   192.168.1.126   worker.blue   <none>           <none>

Now I can try to curl them

curl worker-red:30080
greetings from hello-world-deployment-587468bdb7-hf4dq
curl worker-blue:30080
greetings from hello-world-deployment-587468bdb7-mclhm

That's what happens about half the time. The other half of the time, the curl fails with a timeout error. Specifically - curling worker-red will ONLY yield a response from hf4dq, and curling worker-blue will ONLY yield a response from mclhm. If I cordon and drain worker-blue so both of my pods are running on worker-red, there is never a timeout, and both pods will respond.

It seems like the NodePort service is not reaching pods that are not on the host I am curling. As I understand them, this isn't how services are supposed to work. What am I missing?

[1] If I set up such that I have two workers both on Red, the same problem I'm describing happens, but this is my primary use case so it's the one I'll concentrate on.

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It is hard to simply say what might be wrong here but there are some steps you can take in order to troubleshoot your issue:

  1. Debug Pods, especially check if there is something suspicious in the logs:
  • kubectl logs ${POD_NAME} ${CONTAINER_NAME}

  • kubectl logs --previous ${POD_NAME} ${CONTAINER_NAME}

  1. Debug Services, for example by checking:
  • Does the Service exist?

  • Does the Service work by DNS name?

  • Does the Service work by IP?

  • Is the Service defined correctly?

  • Does the Service have any Endpoints?

  • Is the kube-proxy working?

Going through those steps will help you find the cause of your issue and also better understand the mechanics behind the services.

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