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
  `http://localhost:8080/health`. In this extended syntax `lameduck` will make the process
  unhealthy then wait for 5 seconds before the process is shut down.
* [ready](https://coredns.io/plugins/ready/): An HTTP endpoint on port 8181 will return 200 OK,
  when all plugins that are able to signal readiness have done so.
* [kubernetes](https://coredns.io/plugins/kubernetes/): CoreDNS will reply to DNS queries
  based on IP of the Services and Pods. You can find [more details](https://coredns.io/plugins/kubernetes/)
  about this plugin on the CoreDNS website.
  - `ttl` allows you to set a custom TTL for responses. The default is 5 seconds.
    The minimum TTL allowed is 0 seconds, and the maximum is capped at 3600 seconds.
    Setting TTL to 0 will prevent records from being cached.  
  - The `pods insecure` option is provided for backward compatibility with `kube-dns`.
  - You can use the `pods verified` option, which returns an A record only if there exists a pod
    in the same namespace with a matching IP.
  - The `pods disabled` option can be used if you don't use pod records.
* [prometheus](https://coredns.io/plugins/metrics/): Metrics of CoreDNS are available at
  `http://localhost:9153/metrics` in the [Prometheus](https://prometheus.io/) format
  (also known as OpenMetrics).
* [forward](https://coredns.io/plugins/forward/): Any queries that are not within the Kubernetes