<p>I'm following the Kubernetes install instructions for Helm: <a href="https://docs.cert-manager.io/en/latest/getting-started/install/kubernetes.html" rel="nofollow noreferrer">https://docs.cert-manager.io/en/latest/getting-started/install/kubernetes.html</a>
With Cert-manager v0.81 on K8 v1.15, Ubuntu 18.04 on-premise. 
When I get to testing the installation, I get these errors:</p>

<pre><code>error when creating "test-resources.yaml": Internal error occurred: failed calling webhook "issuers.admission.certmanager.k8s.io": the server is currently unable to handle the request
Error from server (InternalError): error when creating "test-resources.yaml": Internal error occurred: failed calling webhook "certificates.admission.certmanager.k8s.io": the server is currently unable to handle the request
</code></pre>

<p>If I apply the test-resources.yaml before installing with Helm, I'm not getting the errors but it is still not working.
These errors are new to me, as Cert-manager used to work for me on my previous install about a month ago, following the same installation instructions.
I've tried with Cert-Manager 0.72(CRD 0.7) as well as I think that was the last version I managed to get installed but its not working either.</p>

<p>What does these errors mean?</p>

<p><strong>Update</strong>: It turned out to be an internal CoreDNS issue on my cluster. Somehow not being configured correctly. Possible related to wrong POD_CIDR configuration.</p>

<p>If you experience this problem, check the logs of CoreDNS(Or KubeDNS) and you may see lots of errors related to contacting services. Unfortunately, I no longer have the errors.
But this is how I figured out that my network setup was invalid.</p>

<p>I'm using Calico(Will apply for other networks as well) and its network was not set to the same as the POD_CIDR network that I initialized my Kubernetes with.</p>

<p>Example
1. Set up K8: </p>

<pre><code>kubeadm init --pod-network-cidr=10.244.0.0/16
</code></pre>

<ol start="2">
<li><p>Configure Calico.yaml: </p>

<pre><code>- name: CALICO_IPV4POOL_CIDR
  value: "10.244.0.0/16"
</code></pre></li>
</ol>
