---
reviewers:
- bowei
- zihongz
title: Customizing DNS Service
content_type: task
min-kubernetes-server-version: v1.12
weight: 160
---

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This page explains how to configure your DNS
{{< glossary_tooltip text="Pod(s)" term_id="pod" >}} and customize the
DNS resolution process in your cluster.

## {{% heading "prerequisites" %}}

{{< include "task-tutorial-prereqs.md" >}}

Your cluster must be running the CoreDNS add-on.

{{% version-check %}}

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## Introduction

DNS is a built-in Kubernetes service launched automatically
using the _addon manager_ [cluster add-on](https://github.com/kubernetes/kubernetes/blob/master/cluster/addons/addon-manager/README.md).

{{< note >}}
The CoreDNS Service is named `kube-dns` in the `metadata.name` field.  
The intent is to ensure greater interoperability with workloads that relied on
the legacy `kube-dns` Service name to resolve addresses internal to the cluster.
Using a Service named `kube-dns` abstracts away the implementation detail of
which DNS provider is running behind that common name.
{{< /note >}}

If you are running CoreDNS as a Deployment, it will typically be exposed as
a Kubernetes Service with a static IP address.
The kubelet passes DNS resolver information to each container with the
`--cluster-dns=<dns-service-ip>` flag.

DNS names also need domains. You configure the local domain in the kubelet
with the flag `--cluster-domain=<default-local-domain>`.

The DNS server supports forward lookups (A and AAAA records), port lookups (SRV records),
reverse IP address lookups (PTR records), and more. For more information, see
[DNS for Services and Pods](/docs/concepts/services-networking/dns-pod-service/).

If a Pod's `dnsPolicy` is set to `default`, it inherits the name resolution
configuration from the node that the Pod runs on. The Pod's DNS resolution
should behave the same as the node.
But see [Known issues](/docs/tasks/administer-cluster/dns-debugging-resolution/#known-issues).

If you don't want this, or if you want a different DNS config for pods, you can
use the kubelet's `--resolv-conf` flag.  Set this flag to "" to prevent Pods from
inheriting DNS. Set it to a valid file path to specify a file other than
`/etc/resolv.conf` for DNS inheritance.

## CoreDNS

CoreDNS is a general-purpose authoritative DNS server that can serve as cluster DNS,
complying with the [DNS specifications](https://github.com/kubernetes/dns/blob/master/docs/specification.md).

### CoreDNS ConfigMap options

CoreDNS is a DNS server that is modular and pluggable, with plugins adding new functionalities.
The CoreDNS server can be configured by maintaining a [Corefile](https://coredns.io/2017/07/23/corefile-explained/),
which is the CoreDNS configuration file. As a cluster administrator, you can modify the
{{< glossary_tooltip text="ConfigMap" term_id="configmap" >}} for the CoreDNS Corefile to
change how DNS service discovery behaves for that cluster.

In Kubernetes, CoreDNS is installed with the following default Corefile configuration:

```yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: coredns
  namespace: kube-system
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
        cache 30
        loop
        reload
        loadbalance
    }
```

The Corefile configuration includes the following [plugins](https://coredns.io/plugins/) of CoreDNS:

* [errors](https://coredns.io/plugins/errors/): Errors are logged to stdout.
* [health](https://coredns.io/plugins/health/): Health of CoreDNS is reported to