> 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/pmk/how-to/custom-coredns-configuration-for-adding-additional-external-dns.md).

# How To Customize CoreDNS Configuration for Adding Additional External DNS

## Problem

How To Customize CoreDNS Configuration for Adding Additional External DNS.

## Environment

* Platform9 Managed Kubernetes - v5.2 and K8s v1.20 and Higher
* AddOn Management

## Procedure

1. Generate the TOKEN by following steps mentioned in [Keystone Identity](https://platform9.com/learn/keystone-identity).
2. API to retrieve existing CoreDNS ClusterAddon object detail.

{% tabs %}
{% tab title="API GET Call" %}

```python
curl -X GET -H "X-Auth-Token: $TOKEN" https://<DU_FQDN>/qbert/v4/<PROJECT_ID>/sunpike/apis/sunpike.platform9.com/v1alpha2/namespaces/default/clusteraddons/<CLUSTER_UUID>-coredns
```

{% endtab %}
{% endtabs %}

{% tabs %}
{% tab title="Example Showing Default Set Parameters" %}

```typescript
$ curl -X GET -H "X-Auth-Token: $TOKEN" https://cs-sanchit.platform9.horse/qbert/v4/1c1003c1b84e47e7bd2a4cdf3b725976/sunpike/apis/sunpike.platform9.com/v1alpha2/namespaces/default/clusteraddons/8c8f1d62-159a-4829-b68f-3432d4a9afc6-coredns | jq
...
...
  "spec": {
    "clusterID": "8c8f1d62-159a-4829-b68f-3432d4a9afc6",
    "version": "1.7.0",
    "type": "coredns",
    "override": {
      "params": [
        {
          "name": "dnsMemoryLimit",
          "value": "170Mi"
        },
        {
          "name": "dnsDomain",
          "value": "cluster.local"
        }
      ]
    },
    "watch": true
```

{% endtab %}
{% endtabs %}

{% tabs %}
{% tab title="Example Existing Associated ConfigMap" %}

```go
# kubectl describe configmap coredns -n kube-system
Name:         corednsNamespace:    kube-system
Labels:       addonmanager.kubernetes.io/mode=EnsureExists
Annotations:  <none>


Data
====
Corefile:
----
.:53 {
    errors
    health {
        lameduck 5s
    }
    ready
    kubernetes cluster.local in-addr.arpa ip6.arpa {
        pods insecure
        fallthrough in-addr.arpa ip6.arpa
        ttl 30
    }
    prometheus :9153
    forward . /etc/resolv.conf {
        max_concurrent 1000
    }
    cache 30
    loop
    reload
    loadbalance
}

Events:  <none>
```

{% endtab %}
{% endtabs %}

3. Create a new JSON spec file with the required additional DNS configuration parameter.

{% hint style="info" %}
**Note**

The extra DNS configuration parameter one wants to add should have no indentations. The addon operator adds the correct indentation before adding it under the DNS block in the configmap.
{% endhint %}

{% tabs %}
{% tab title="Sample DNS configuration without indentation" %}

```go
kfplc.com:53 {
   errors
   cache 30
   forward . 10.246.6.1
}
```

{% endtab %}
{% endtabs %}

{% tabs %}
{% tab title="base64 Encoding of the sample configuration" %}

```go
a2ZwbGMuY29tOjUzIHsKICBlcnJvcnMKICBjYWNoZSAzMAogIGZvcndhcmQgLiAxMC4yNDYuNi4xCn0K
```

{% endtab %}
{% endtabs %}

This needs to be inputted as a value for the parameter *`base64EncAdditionalDnsConfig`* in the JSON spec file.

{% tabs %}
{% tab title="Sample JSON File" %}

```go
# cat coredns.json
{
    "apiVersion": "sunpike.platform9.com/v1alpha2",
    "kind": "ClusterAddon",
    "metadata": {
        "labels": {
            "sunpike.pf9.io/cluster": "CLUSTER_UUID",
            "type": "coredns"
        },
        "name": "CLUSTER_UUID-coredns",
        "namespace": "default"
    },
    "spec": {
        "clusterID": "CLUSTER_UUID",
        "override": {
            "params": [
                {
                    "name": "dnsMemoryLimit",
                    "value": "170Mi"
                },
                {
                    "name": "dnsDomain",
                    "value": "cluster.local"
                },
                {
                    "name": "base64EncAdditionalDnsConfig",
                    "value": "<base 64 encoded additional dns config>"
                }
            ]
        },
        "type": "coredns",
        "version": "1.7.0",
        "watch": true
    }
}
```

{% endtab %}
{% endtabs %}

You can read more about it here [CoreDNS Addon](https://platform9.com/docs/kubernetes/coredns-addon).

4. Patch the existing CoreDNS ClusterAddon object with the newly created Spec file *coredns.json*.

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

```go
curl -X PATCH -H "X-Auth-Token: $TOKEN" -H "Content-Type: application/merge-patch+json" -H "Accept: application/json" -d "@coredns.json" https://<DU_FQDN>/qbert/v4/<PROJECT_ID>/sunpike/apis/sunpike.platform9.com/v1alpha2/namespaces/default/clusteraddons/<CLUSTER_UUID>-coredns
```

{% endtab %}
{% endtabs %}

{% hint style="info" %}
**Info**

Replace the placeholders `<DU_FQDN>`, `<PROJECT_ID>` and the `<CLUSTER_UUID>` with their appropriate values required. The `name` attribute in the spec must be in the format `CLUSTER_UUID-coredns`

The CoreDNS version in the above JSON file is currently on *1.7.0*. It will be updated along with the `pf9-kube` version and can be referred from the [Support Matrix.](https://docs.platform9.com/kubernetes/support-matrix)
{% endhint %}

{% tabs %}
{% tab title="Updated ConfigMap after the PATCH API Call" %}

```go
# kubectl describe configmap coredns -n kube-system
Name:         coredns
Namespace:    kube-system
Labels:       addonmanager.kubernetes.io/mode=EnsureExists
Annotations:  <none>

Data
====
Corefile:
----
.:53 {
    errors
    health {
        lameduck 5s
    }
    ready
    kubernetes cluster.local in-addr.arpa ip6.arpa {
        pods insecure
        fallthrough in-addr.arpa ip6.arpa
        ttl 30
    }

    prometheus :9153
    forward . /etc/resolv.conf {
        max_concurrent 1000
    }
    cache 30
    loop
    reload
    loadbalance

}

kfplc.com:53 {
  errors
  cache 30
  forward . 10.246.6.1
}​


Events:  <none>
```

{% endtab %}
{% endtabs %}

{% hint style="info" %}
**Note**

The changes made to the AddOn object will persist across management plane & cluster upgrades.
{% endhint %}


---

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