<p>I create a <code>k8s</code> cluster by <code>kops</code> on <code>aws</code>, the node auto scaling group configuration like:</p>

<pre><code>metadata:
creationTimestamp: "2017-03-21T03:53:26Z"
name: nodes
spec:
  associatePublicIp: true
  image: kope.io/k8s-1.4-debian-jessie-amd64-hvm-ebs-2016-10-21
  machineType: t2.medium
  maxSize: 5
  minSize: 2
  role: Node
  zones:
  - us-west-1a
  - us-west-1c
</code></pre>

<p>the <code>aws</code> console shows current asg like: </p>

<pre><code>desired:2; min:2; max:5
</code></pre>

<p>then I install the <code>add-ons</code> --- <code>cluster-autoscaler</code> by using the <a href="https://github.com/kubernetes/contrib/blob/master/cluster-autoscaler/cloudprovider/aws/README.md" rel="nofollow noreferrer">official doc</a>, then I deploy a pod which current cluster can't supply the resource, but <code>cluster-autoscaler</code> doesn't add the node to the cluster, logs is like below:</p>

<pre><code>admin@ip-10-0-52-252:/var/log$kubectl logs -f cluster-autoscaler-1581749901-fqbzk -n kube-system
I0322 07:08:43.407683       1 event.go:216] Event(api.ObjectReference{Kind:"Pod", Namespace:"default", Name:"new-mq-test-951523717-trd2s", UID:"9437ac54-0ecd-11e7-8779-0257a5d4c012", APIVersion:"v1", ResourceVersion:"189546", FieldPath:""}): type: 'Normal' reason: 'NotTriggerScaleUp' pod didn't trigger scale-up (it wouldn't fit if a new node is added)
I0322 07:08:43.407910       1 event.go:216] Event(api.ObjectReference{Kind:"Pod", Namespace:"default", Name:"new-mq-test-951523717-n986l", UID:"9437a3db-0ecd-11e7-8779-0257a5d4c012", APIVersion:"v1", ResourceVersion:"189543", FieldPath:""}): type: 'Normal' reason: 'NotTriggerScaleUp' pod didn't trigger scale-up (it wouldn't fit if a new node is added)
</code></pre>

<p>so why the <code>cluster-autoscaler</code> doesn't scale up the cluster by adding the ec2 nodes ? any answers are very appreciated</p>

<p>finally I found the answer, my default <code>kops</code> configuration of <code>nodes</code> asg is <code>t2.medium</code>, while I deploy the pod which require a <code>5000M</code> for memory, as we all konw <code>t2.medium</code> memory is <code>4GB</code> which can't fit the requirement, so the <code>cluster-autoscaler</code> can't scale up!</p>
