Service dispatches all traffic to one of PODs created by replication controller

Question

I have a Replication Controller which creates more than one PODs. Within each POD, there is a container running an application.

Now within the container, it can call kubernetes API as below.

KUBE_TOKEN=$(</var/run/secrets/kubernetes.io/serviceaccount/token)
curl --silent --insecure --header "Authorization: Bearer $KUBE_TOKEN"  \
      https://$KUBERNETES_SERVICE_HOST:$KUBERNETES_PORT_443_TCP_PORT/api/v1/namespaces/$POD_NAMESPACE/pods/$POD_NAME

POD_NAME is the name of the POD; POD_NAMESPACE is the namespace of the POD

The application instances in contains make up a cluster. And they elect one of the application instances as master, the others are slaves which replicates the data from master in real-time. When the master instance fails, another slave instance will be promoted to master.

When the application in the container is promoted to master, I want the master application instance to call the kubernetes API so that all the traffic goes to this POD/container.

{
  "kind": "Service",
  "apiVersion": "v1",
  "metadata": {
    "name": "my-cluster"
  },
  "spec": {
    "ports": [{
      "port": 33379,
      "targetPort": 33379
    }],
    "type" : "None",
    "selector": {
      "name": "<POD_NAME>"
    }
  }
}

I specified the POD_NAME as the selector, but the service can not find any of the POD.

How can I configure the service so that all the traffic goes to that POD?

score 0 · Accepted Answer · answered Mar 15 '16 at 17:51

You could have your service selector select a "master" label, e.g. "role": "master" - then you can add the master label to whichever pod is chosen as the master. Labels can be changed on running pods using PATCH method.

I specified the POD_NAME as the selector, but the service can not find any of the POD.

The name label is treated the same as any other label in a selector. There is a common practice to add a name label to a pod that matches the metadata name, and then use that in a selector, but without the label on the pod the selector won't find it.

Service dispatches all traffic to one of PODs created by replication controller

1 Answers1