> For the complete documentation index, see [llms.txt](https://platform9.com/kb/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://platform9.com/kb/pcd-ts/kubernetes-clusters/troubleshooting-calico-add-onq6m.md).

# Troubleshooting CoreDNS Add-on

Troubleshoot CoreDNS issues in PCD-K clusters effectively. Follow our guide for checking pod status, error states, and DNS service endpoints in Kubernetes. Ensure optimal DNS resolution and contact Pl

## 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.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters:

```
GET https://platform9.com/kb/pcd-ts/kubernetes-clusters/troubleshooting-calico-add-onq6m.md?ask=<question>&goal=<user_goal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `build a script that syncs our docs to a CMS` lets GitBook tailor the answer to that use case.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.