<p>I have setup a Kubernetes cluster with one master (kube-master) and 2 slaves (kube-node-01 and kube-node-02)</p>
<p>All was running fine ... now after debian stretch -&gt; buster upgrade my coredns pods are failing with <code>CrashLoopBackOff</code> for some reason.</p>
<p>I did a <code>kubectl describe</code> and the error is <code>Readiness probe failed: HTTP probe failed with statuscode: 503</code></p>
<p>The Readiness url looks suspicious to me <code>http-get http://:8080/health delay=0s timeout=1s period=10s #success=1 #failure=3</code> ... there is no hostname !? is that correct?</p>
<p>The <code>Liveness</code> property also does not have a hostname.</p>
<p>All vm's are pingable from each other.</p>
<p>Any ideas?</p>

<p>I met similar issue when upgrade my host machine to ubuntu 18.04 which uses systemd-resolved as DNS server. The nameserver field in /etc/resolv.conf is using a local IP address 127.0.0.53 which would cause coreDNS failed to start.</p>

<p>You can take a look at the details from the following link.
<a href="https://github.com/coredns/coredns/blob/master/plugin/loop/README.md#troubleshooting-loops-in-kubernetes-clusters" rel="nofollow noreferrer">https://github.com/coredns/coredns/blob/master/plugin/loop/README.md#troubleshooting-loops-in-kubernetes-clusters</a></p>
