# Troubleshooting CoreDNS Add-on

## Problem

CoreDNS handles DNS resolution for PCD-K clusters. As a critical core add-on and the default DNS server in Kubernetes, broken CoreDNS functionality directly impacts DNS request resolution. When CoreDNS experiences such issues, here's a general guide on how to troubleshoot CoreDNS add-on problems.

## Environment

* Private Cloud Director - v2025.4 and Higher.
* Kubernetes Cluster - 1.31.2 or Higher.

## Procedure

1. CoreDNS is deployed as a deployment in the `kube-system` namespace. Verify the pod status in the namespace using command:

{% tabs %}
{% tab title="Command" %}

```bash
$ kubectl get pods -n kube-system
```

{% endtab %}
{% endtabs %}

2. Review why these pods are in "`CrashLoopBackOff/OOMkilled/Pending/Error`" state, see events sections in below command output.

```bash
$ kubectl describe <pod-name> -n <calico-namespace>
```

3. Get more information on the failure from pod logs using command:

{% tabs %}
{% tab title="Command" %}

```bash
$ kubectl logs <pod-name> -n <kube-system>
```

{% endtab %}
{% endtabs %}

4. Validate if the `kube-dns` service is showing the correct CoreDNS pods endpoints using command:

{% tabs %}
{% tab title="Command" %}

```bash
$ kubectl describe svc -n kube-system kube-dns
```

{% endtab %}
{% endtabs %}

5. SSH to a worker node and check its `_/etc/resolv.conf_`. Are the upstream DNS servers correct and reachable from the node?
6. If these steps prove insufficient to resolve the issue, kindly reach out to the [Platform9 Support Team](https://support.platform9.com/) for additional assistance.

## Most common causes

* The upstream DNS Server Unreachability, usually from `_/etc/resolv.conf_` of the worker node.
* CoreDNS connectivity to the Kubernetes API server is down.


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