<p>I'd like to run a 'job' per node, one pod on a node at a time.</p>

<ul>
<li>I've scheduled a bunch of jobs</li>
<li>I have a whole bunch of pending pods now</li>
<li>I'd like these pending pods to now trigger a node scaling up event (which does <strong>NOT</strong> happen)</li>
</ul>

<hr>

<p>Very much like this issue (made by myself): <a href="https://stackoverflow.com/questions/54314246/kubernetes-reports-pod-didnt-trigger-scale-up-it-wouldnt-fit-if-a-new-node-i">Kubernetes reports &quot;pod didn&#39;t trigger scale-up (it wouldn&#39;t fit if a new node is added)&quot; even though it would?</a></p>

<p>However in this case it should indeed fit on a new node.</p>

<p>How can I diagnose why Kubernetes has determined that a node scaling event is not possible?</p>

<p>My job yaml:</p>

<pre><code>apiVersion: batch/v1
kind: Job
metadata:
  name: example-job-${job_id}
  labels:
    job-in-progress: job-in-progress-yes
spec:
  template:
    metadata:
      name: example-job-${job_id}
    spec:
      # this bit ensures a job/container does not get scheduled along side another - 'anti' affinity
      affinity:
        podAntiAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
          - topologyKey: kubernetes.io/hostname 
            labelSelector:
              matchExpressions:
              - key: job-in-progress
                operator: NotIn
                values:
                - job-in-progress-yes
      containers:
      - name: buster-slim
        image: debian:buster-slim
        command: ["bash"]
        args: ["-c", "sleep 60; echo ${echo_param}"]
      restartPolicy: Never
</code></pre>

<p>Autoscaler logs:</p>

<pre><code>I0920 19:27:58.190751       1 static_autoscaler.go:128] Starting main loop
I0920 19:27:58.261972       1 auto_scaling_groups.go:320] Regenerating instance to ASG map for ASGs: []
I0920 19:27:58.262003       1 aws_manager.go:152] Refreshed ASG list, next refresh after 2019-09-20 19:28:08.261998185 +0000 UTC m=+302.102284346
I0920 19:27:58.262092       1 static_autoscaler.go:261] Filtering out schedulables
I0920 19:27:58.264212       1 static_autoscaler.go:271] No schedulable pods
I0920 19:27:58.264246       1 scale_up.go:262] Pod default/example-job-21-npv6p is unschedulable
I0920 19:27:58.264252       1 scale_up.go:262] Pod default/example-job-28-zg4f8 is unschedulable
I0920 19:27:58.264258       1 scale_up.go:262] Pod default/example-job-24-fx9rd is unschedulable
I0920 19:27:58.264263       1 scale_up.go:262] Pod default/example-job-6-7mvqs is unschedulable
I0920 19:27:58.264268       1 scale_up.go:262] Pod default/example-job-20-splpq is unschedulable
I0920 19:27:58.264273       1 scale_up.go:262] Pod default/example-job-25-g5mdg is unschedulable
I0920 19:27:58.264279       1 scale_up.go:262] Pod default/example-job-16-wtnw4 is unschedulable
I0920 19:27:58.264284       1 scale_up.go:262] Pod default/example-job-7-g89cp is unschedulable
I0920 19:27:58.264289       1 scale_up.go:262] Pod default/example-job-8-mglhh is unschedulable
I0920 19:27:58.264323       1 scale_up.go:304] Upcoming 0 nodes
I0920 19:27:58.264370       1 scale_up.go:420] No expansion options
I0920 19:27:58.264511       1 static_autoscaler.go:333] Calculating unneeded nodes
I0920 19:27:58.264533       1 utils.go:474] Skipping ip-10-0-1-118.us-west-2.compute.internal - no node group config
I0920 19:27:58.264542       1 utils.go:474] Skipping ip-10-0-0-65.us-west-2.compute.internal - no node group config
I0920 19:27:58.265063       1 factory.go:33] Event(v1.ObjectReference{Kind:"Pod", Namespace:"default", Name:"example-job-25-g5mdg", UID:"d2e0e48c-dbd9-11e9-a9e2-024e7db9d360", APIVersion:"v1", ResourceVersion:"7256", FieldPath:""}): type: 'Normal' reason: 'NotTriggerScaleUp' pod didn't trigger scale-up (it wouldn't fit if a new node is added): 
I0920 19:27:58.265090       1 factory.go:33] Event(v1.ObjectReference{Kind:"Pod", Namespace:"default", Name:"example-job-8-mglhh", UID:"c7d3ce78-dbd9-11e9-a9e2-024e7db9d360", APIVersion:"v1", ResourceVersion:"7267", FieldPath:""}): type: 'Normal' reason: 'NotTriggerScaleUp' pod didn't trigger scale-up (it wouldn't fit if a new node is added): 
I0920 19:27:58.265101       1 factory.go:33] Event(v1.ObjectReference{Kind:"Pod", Namespace:"default", Name:"example-job-6-7mvqs", UID:"c6a5b0e4-dbd9-11e9-a9e2-024e7db9d360", APIVersion:"v1", ResourceVersion:"7273", FieldPath:""}): type: 'Normal' reason: 'NotTriggerScaleUp' pod didn't trigger scale-up (it wouldn't fit if a new node is added): 
I0920 19:27:58.265110       1 factory.go:33] Event(v1.ObjectReference{Kind:"Pod", Namespace:"default", Name:"example-job-20-splpq", UID:"cfeb9521-dbd9-11e9-a9e2-024e7db9d360", APIVersion:"v1", ResourceVersion:"7259", FieldPath:""}): type: 'Normal' reason: 'NotTriggerScaleUp' pod didn't trigger scale-up (it wouldn't fit if a new node is added): 
I0920 19:27:58.265363       1 factory.go:33] Event(v1.ObjectReference{Kind:"Pod", Namespace:"default", Name:"example-job-21-npv6p", UID:"d084c067-dbd9-11e9-a9e2-024e7db9d360", APIVersion:"v1", ResourceVersion:"7275", FieldPath:""}): type: 'Normal' reason: 'NotTriggerScaleUp' pod didn't trigger scale-up (it wouldn't fit if a new node is added): 
I0920 19:27:58.265384       1 factory.go:33] Event(v1.ObjectReference{Kind:"Pod", Namespace:"default", Name:"example-job-16-wtnw4", UID:"ccbe48e0-dbd9-11e9-a9e2-024e7db9d360", APIVersion:"v1", ResourceVersion:"7265", FieldPath:""}): type: 'Normal' reason: 'NotTriggerScaleUp' pod didn't trigger scale-up (it wouldn't fit if a new node is added): 
I0920 19:27:58.265490       1 factory.go:33] Event(v1.ObjectReference{Kind:"Pod", Namespace:"default", Name:"example-job-28-zg4f8", UID:"d4afc868-dbd9-11e9-a9e2-024e7db9d360", APIVersion:"v1", ResourceVersion:"7269", FieldPath:""}): type: 'Normal' reason: 'NotTriggerScaleUp' pod didn't trigger scale-up (it wouldn't fit if a new node is added): 
I0920 19:27:58.265515       1 factory.go:33] Event(v1.ObjectReference{Kind:"Pod", Namespace:"default", Name:"example-job-24-fx9rd", UID:"d24975e5-dbd9-11e9-a9e2-024e7db9d360", APIVersion:"v1", ResourceVersion:"7271", FieldPath:""}): type: 'Normal' reason: 'NotTriggerScaleUp' pod didn't trigger scale-up (it wouldn't fit if a new node is added): 
I0920 19:27:58.265685       1 static_autoscaler.go:360] Scale down status: unneededOnly=true lastScaleUpTime=2019-09-20 19:23:23.822104264 +0000 UTC m=+17.662390361 lastScaleDownDeleteTime=2019-09-20 19:23:23.822105556 +0000 UTC m=+17.662391653 lastScaleDownFailTime=2019-09-20 19:23:23.822106849 +0000 UTC m=+17.662392943 scaleDownForbidden=false isDeleteInProgress=false
I0920 19:27:58.265910       1 factory.go:33] Event(v1.ObjectReference{Kind:"Pod", Namespace:"default", Name:"example-job-7-g89cp", UID:"c73cfaea-dbd9-11e9-a9e2-024e7db9d360", APIVersion:"v1", ResourceVersion:"7263", FieldPath:""}): type: 'Normal' reason: 'NotTriggerScaleUp' pod didn't trigger scale-up (it wouldn't fit if a new node is added): 
</code></pre>

<p>I had the wrong parameters defined on the autoscaler.</p>
<p>I had to modify the <code>node-group-auto-discovery</code> and <code>nodes</code> parameters.</p>
<pre><code>        - ./cluster-autoscaler
        - --cloud-provider=aws
        - --namespace=default
        - --scan-interval=25s
        - --scale-down-unneeded-time=30s
        - --nodes=1:20:terraform-eks-demo20190922161659090500000007--terraform-eks-demo20190922161700651000000008
        - --node-group-auto-discovery=asg:tag=k8s.io/cluster-autoscaler/enabled,k8s.io/cluster-autoscaler/example-job-runner
        - --logtostderr=true
        - --stderrthreshold=info
        - --v=4

</code></pre>
<p>When installing the cluster autoscaler it is not enough to simply apply the example config, e.g.:</p>
<pre><code>kubectl apply -f https://raw.githubusercontent.com/kubernetes/autoscaler/master/cluster-autoscaler/cloudprovider/aws/examples/cluster-autoscaler-autodiscover.yaml
</code></pre>
<p>As documented in <a href="https://docs.aws.amazon.com/eks/latest/userguide/cluster-autoscaler.html" rel="nofollow noreferrer">the user guide</a>, that config has placeholder for your eks cluster name in the value for <code>node-group-auto-discovery</code>, and you must either replace it before applying, or update it after deploying.</p>
