Select node where the other POD does not exist

Question

I have two nodes

gke-1789571565414321321-a3ec9151-node-q0cz gke-98798532417432432421-a3ec9151-node-q0cz

And I have two ReplicationController to deploy 2 pods, xxx & yyy.

What I want to: If xxx is deployed on one of the node, yyy should go to the other.

I implement this by spec.nodeName property.

Is there a generic way to avoid indicating the specific node?

xxx:

{
  "apiVersion": "v1",
  "kind": "ReplicationController",
  "metadata": {
    "name": "xxx",
    "labels": { "name" : "xxx" }
  },
  "spec": {  
    "replicas": 1,
    "selector": {
      "name":"xxx"
    },
    "template": { 
      "metadata": {
        "labels": {
          "name":"xxx"
        }
      },
      "spec": { 
        "containers": [
          //...
        ],
        "nodeName" : "gke-1789571565414321321-a3ec9151-node-q0cz"
      }
    }
  }
}

yyy:

{
  "apiVersion": "v1",
  "kind": "ReplicationController",
  "metadata": {
    "name": "yyy",
    "labels": { "name" : "yyy" }
  },
  "spec": {  
    "replicas": 1,
    "selector": {
      "name":"yyy"
    },
    "template": { 
      "metadata": {
        "labels": {
          "name":"yyy"
        }
      },
      "spec": { 
        "containers": [
          //...
        ],
        "nodeName" : "gke-98798532417432432421-a3ec9151-node-q0cz"
      }
    }
  }
}

Answer 1

The feature you are looking for is called "anti-affinity" and is not yet implemented (but is described in a design doc in github). Until then, you can force the pods to be spread by assigning a constraint that can only be met once per node, such as a host port (see Allow only one pod of a type on a node in Kubernetes).