2016-02-11 00:55:31 +00:00
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---
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---
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2016-02-26 11:54:48 +00:00
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As of Kubernetes 0.8, DNS is offered as a [cluster add-on](http://releases.k8s.io/{{page.githubbranch}}/cluster/addons/README.md).
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If enabled, a DNS Pod and Service will be scheduled on the cluster, and the kubelets will be
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configured to tell individual containers to use the DNS Service's IP to resolve DNS names.
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Every Service defined in the cluster (including the DNS server itself) will be
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assigned a DNS name. By default, a client Pod's DNS search list will
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include the Pod's own namespace and the cluster's default domain. This is best
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illustrated by example:
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Assume a Service named `foo` in the Kubernetes namespace `bar`. A Pod running
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in namespace `bar` can look up this service by simply doing a DNS query for
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`foo`. A Pod running in namespace `quux` can look up this service by doing a
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DNS query for `foo.bar`.
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The cluster DNS server ([SkyDNS](https://github.com/skynetservices/skydns))
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supports forward lookups (A records) and service lookups (SRV records).
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## How it Works
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2016-03-06 12:26:30 +00:00
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The running DNS pod holds 4 containers - skydns, etcd (a private instance which skydns uses),
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a Kubernetes-to-skydns bridge called kube2sky, and a health check called healthz. The kube2sky process
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2016-02-26 11:54:48 +00:00
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watches the Kubernetes master for changes in Services, and then writes the
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information to etcd, which skydns reads. This etcd instance is not linked to
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any other etcd clusters that might exist, including the Kubernetes master.
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## Issues
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The skydns service is reachable directly from Kubernetes nodes (outside
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of any container) and DNS resolution works if the skydns service is targeted
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explicitly. However, nodes are not configured to use the cluster DNS service or
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to search the cluster's DNS domain by default. This may be resolved at a later
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time.
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## For more information
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See [the docs for the DNS cluster addon](http://releases.k8s.io/{{page.githubbranch}}/cluster/addons/dns/README.md).
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