<p>From what I understand, using multiple replicas as well as auto-scaling is supposed to help in the case that lots of people visit your website and make calls to services provided by your Kubernetes cluster.<br> </p>

<p>How do the replicas help with scaling?<br></p>

<p>Aren't these extra pods all just running on the same computer with constant resources?<br> That would mean that they're all limited by a constant amount of CPU and memory.</p>

<p>Kubernetes has couple of scaling mechanisms. Horizontal Pod Autoscaler being the basic, but not the only one.</p>

<p>With HPA you can spin up additional PODs according to some metrics (most commonly cpu and memory). At some point you will hit a moment when your cluster nodes do not have enough resources to satisfy resource requirements of your pods (you will have pods in <code>Pending</code> state due to lack of nodes available for scheduling).</p>

<p>At that point a Cluster Autoscaler can kick in and ie. scale AWS ASG (or some other cloud-ish node pool) to add new node to the cluster and make space for the pending pod(s)</p>
