<ol>
<li>How many CRs of a certain CRD can a k8s cluster handle?</li>
<li>How many CRs can a certain controller (or Operator) reconcile?</li>
</ol>
<p>Thanks!</p>

<p><strong>1. How many CRs of a certain CRD can a k8s cluster handle?</strong></p>
<p>As many as your API server's <a href="https://kubernetes.io/docs/concepts/extend-kubernetes/api-extension/custom-resources/#storage" rel="nofollow noreferrer">storage space allows</a>:</p>
<blockquote>
<p>Custom resources consume storage space in the same way that ConfigMaps
do. Creating too many custom resources may overload your API server's
storage space.</p>
<p>Aggregated API servers may use the same storage as the main API
server, in which case the same warning applies.</p>
</blockquote>
<p><strong>2. How many CRs can a certain controller (or Operator) reconcile?</strong></p>
<p>A controller in Kubernetes keeps track of <strong>at least one resource type</strong>. There many built-in controllers in Kubernetes, replication controller, namespace controller, service account controller, etc. Custom Resource definition along with Custom Controller makes the <a href="https://kubernetes.io/docs/concepts/extend-kubernetes/operator/" rel="nofollow noreferrer">Operator Pattern</a>. It's hard to tell what is the maximum CR that a given Operator could handle as it would depend on different aspects such as the Operator itself. For example, <a href="https://01.org/kubernetes/blogs/2020/using-kubernetes-custom-controller-manage-two-custom-resources-designing-akraino-icn-bpa" rel="nofollow noreferrer">this guide</a> shows that the Binary Provisioning Agent (BPA) Custom Controller can handle two or more custom resources.</p>
<p>You can find some useful sources below:</p>
<ul>
<li><p><a href="https://kubernetes.io/docs/concepts/extend-kubernetes/api-extension/custom-resources/#storage" rel="nofollow noreferrer">Custom Resources</a></p>
</li>
<li><p><a href="https://kubernetes.io/docs/concepts/extend-kubernetes/operator/" rel="nofollow noreferrer">Operator pattern</a></p>
</li>
<li><p><a href="https://01.org/kubernetes/blogs/2020/using-kubernetes-custom-controller-manage-two-custom-resources-designing-akraino-icn-bpa" rel="nofollow noreferrer">Using a Kubernetes custom controller to manage two custom resources</a></p>
</li>
<li><p><a href="https://admiralty.io/blog/2018/06/27/kubernetes-custom-resource-controller-and-operator-development-tools/" rel="nofollow noreferrer">Kubernetes Custom Resource, Controller and Operator Development Tools</a></p>
</li>
</ul>
