Update documentation on CoreDNS (#10923)
* update documentation on CoreDNS * Update dns-custom-nameservers.md Fixed nit noted in comments and cleaned up a few more things while I was in there. This whole topic needs a complete redo, but this PR is an iterative improvment. Thanks!
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Sandeep Rajan
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@@ -122,7 +122,7 @@ about the [service proxy](/docs/concepts/services-networking/service/#virtual-ip
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Kubernetes supports 2 primary modes of finding a Service - environment variables
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and DNS. The former works out of the box while the latter requires the
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[kube-dns cluster addon](http://releases.k8s.io/{{< param "githubbranch" >}}/cluster/addons/dns/kube-dns/README.md).
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[CoreDNS cluster addon](http://releases.k8s.io/{{< param "githubbranch" >}}/cluster/addons/dns/coredns).
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### Environment Variables
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@@ -178,7 +178,7 @@ kube-dns ClusterIP 10.0.0.10 <none> 53/UDP,53/TCP 8m
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If it isn't running, you can [enable it](http://releases.k8s.io/{{< param "githubbranch" >}}/cluster/addons/dns/README.md#how-do-i-configure-it).
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The rest of this section will assume you have a Service with a long lived IP
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(my-nginx), and a DNS server that has assigned a name to that IP (the kube-dns
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(my-nginx), and a DNS server that has assigned a name to that IP (the CoreDNS
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cluster addon), so you can talk to the Service from any pod in your cluster using
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standard methods (e.g. gethostbyname). Let's run another curl application to test this:
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@@ -258,6 +258,9 @@ kubectl -n kube-system get deployment coredns -o yaml | \
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kubectl apply -f -
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```
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Another cause for CoreDNS to have `CrashLoopBackOff` is when a CoreDNS Pod deployed in Kubernetes detects a loop. [A number of workarounds](https://github.com/coredns/coredns/tree/master/plugin/loop#troubleshooting-loops-in-kubernetes-clusters)
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are available to avoid Kubernetes trying to restart the CoreDNS Pod every time CoreDNS detects the loop and exits.
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{{< warning >}}
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Disabling SELinux or setting `allowPrivilegeEscalation` to `true` can compromise
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the security of your cluster.
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@@ -134,11 +134,11 @@ You'll see a list of pods that looks something like this (the name specifics wil
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```shell
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NAMESPACE NAME READY STATUS RESTARTS AGE
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kube-system coredns-5f4fbb68df-mc8z8 1/1 Running 0 15m
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kube-system fluentd-cloud-logging-kubernetes-minion-63uo 1/1 Running 0 14m
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kube-system fluentd-cloud-logging-kubernetes-minion-c1n9 1/1 Running 0 14m
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kube-system fluentd-cloud-logging-kubernetes-minion-c4og 1/1 Running 0 14m
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kube-system fluentd-cloud-logging-kubernetes-minion-ngua 1/1 Running 0 14m
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kube-system kube-dns-v5-7ztia 3/3 Running 0 15m
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kube-system kube-ui-v1-curt1 1/1 Running 0 15m
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kube-system monitoring-heapster-v5-ex4u3 1/1 Running 1 15m
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kube-system monitoring-influx-grafana-v1-piled 2/2 Running 0 15m
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@@ -63,6 +63,11 @@ value to `false`:
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kubeadm init --feature-gates=CoreDNS=false
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```
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## Tuning CoreDNS
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When resource utilisation is a concern, it may be useful to tune the configuration of CoreDNS. For more details, check out the
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[documentation on scaling CoreDNS]((https://github.com/coredns/deployment/blob/master/kubernetes/Scaling_CoreDNS.md)).
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{{% /capture %}}
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{{% capture whatsnext %}}
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@@ -103,10 +103,10 @@ The Corefile configuration includes the following [plugins](https://coredns.io/p
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* [proxy](https://coredns.io/plugins/proxy/): Any queries that are not within the cluster domain of Kubernetes will be forwarded to predefined resolvers (/etc/resolv.conf).
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* [cache](https://coredns.io/plugins/cache/): This enables a frontend cache.
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* [loop](https://coredns.io/plugins/loop/): Detects simple forwarding loops and halts the CoreDNS process if a loop is found.
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* [reload](https://coredns.io/plugins/reload): Allows automatic reload of a changed Corefile.
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* [loadbalance](https://coredns.io/plugins/loadbalance): This is a round-robin DNS loadbalancer by randomizing the order of A, AAAA, and MX records in the answer.
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* [reload](https://coredns.io/plugins/reload): Allows automatic reload of a changed Corefile. After you edit the ConfigMap configuration, allow two minutes for your changes to take effect.
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* [loadbalance](https://coredns.io/plugins/loadbalance): This is a round-robin DNS loadbalancer that randomizes the order of A, AAAA, and MX records in the answer.
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We can modify the default behavior by modifying this configmap.
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You can modify the default CoreDNS behavior by modifying the ConfigMap.
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### Configuration of Stub-domain and upstream nameserver using CoreDNS
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@@ -132,7 +132,7 @@ proxy . 172.16.0.1
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upstream 172.16.0.1
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```
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So, the final ConfigMap along with the default `Corefile` configuration will look like:
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The final ConfigMap along with the default `Corefile` configuration looks like:
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```yaml
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apiVersion: v1
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@@ -307,9 +307,9 @@ data:
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## CoreDNS configuration equivalent to kube-dns
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CoreDNS supports all the functionalities and more that is provided by kube-dns.
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CoreDNS supports the features of kube-dns and more.
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A ConfigMap created for kube-dns to support `StubDomains`and `upstreamNameservers` translates to the `proxy` plugin in CoreDNS.
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Similarly, the `Federation` plugin translates to the `federation` plugin in CoreDNS.
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Similarly, the `Federations` plugin in kube-dns translates to the `federation` plugin in CoreDNS.
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### Example
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@@ -380,12 +380,10 @@ The complete Corefile with the default plugins:
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}
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```
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In Kubernetes version 1.10 and later, kubeadm supports automatic translation of the CoreDNS ConfigMap from the kube-dns ConfigMap.
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## Migration to CoreDNS
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To migrate from kube-dns to CoreDNS, [a detailed blog](https://coredns.io/2018/05/21/migration-from-kube-dns-to-coredns/) is available to help users adapt CoreDNS in place of kube-dns.
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A cluster administrator can also migrate using [the deploy script](https://github.com/coredns/deployment/blob/master/kubernetes/deploy.sh), which will also help you translate the kube-dns configmap to the equivalent CoreDNS one.
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A cluster administrator can also migrate using [the deploy script](https://github.com/coredns/deployment/blob/master/kubernetes/deploy.sh).
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## What's next
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- [Debugging DNS Resolution](/docs/tasks/administer-cluster/dns-debugging-resolution/).
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