Merge pull request #1956 from rajansandeep/corednskep
KEP for CoreDNS to GA.
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kep-number: 10
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title: Graduate CoreDNS to GA
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authors:
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- "@johnbelamaric"
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- "@rajansandeep"
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owning-sig: sig-network
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participating-sigs:
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- sig-cluster-lifecycle
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reviewers:
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- "@bowei"
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- "@thockin"
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approvers:
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- "@thockin"
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editor: "@rajansandeep"
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creation-date: 2018-03-21
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last-updated: 2018-05-18
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status: provisional
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see-also: https://github.com/kubernetes/community/pull/2167
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---
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# Graduate CoreDNS to GA
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## Table of Contents
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* [Summary](#summary)
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* [Motivation](#motivation)
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* [Goals](#goals)
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* [Non-Goals](#non-goals)
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* [Proposal](#proposal)
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* [User Cases](#use-cases)
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* [Graduation Criteria](#graduation-criteria)
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* [Implementation History](#implementation-history)
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## Summary
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CoreDNS is sister CNCF project and is the successor to SkyDNS, on which kube-dns is based. It is a flexible, extensible
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authoritative DNS server and directly integrates with the Kubernetes API. It can serve as cluster DNS,
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complying with the [dns spec](https://git.k8s.io/dns/docs/specification.md). As an independent project,
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it is more actively developed than kube-dns and offers performance and functionality beyond what kube-dns has. For more details, see the [introductory presentation](https://docs.google.com/presentation/d/1v6Coq1JRlqZ8rQ6bv0Tg0usSictmnN9U80g8WKxiOjQ/edit#slide=id.g249092e088_0_181), or [coredns.io](https://coredns.io), or the [CNCF webinar](https://youtu.be/dz9S7R8r5gw).
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Currently, we are following the road-map defined [here](https://github.com/kubernetes/features/issues/427). CoreDNS is Beta in Kubernetes v1.10, which can be installed as an alternate to kube-dns.
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The purpose of this proposal is to graduate CoreDNS to GA.
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## Motivation
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* CoreDNS is more flexible and extensible than kube-dns.
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* CoreDNS is easily extensible and maintainable using a plugin architecture.
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* CoreDNS has fewer moving parts than kube-dns, taking advantage of the plugin architecture, making it a single executable and single process.
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* It is written in Go, making it memory-safe (kube-dns includes dnsmasq which is not).
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* CoreDNS has [better performance](https://github.com/kubernetes/community/pull/1100#issuecomment-337747482) than [kube-dns](https://github.com/kubernetes/community/pull/1100#issuecomment-338329100) in terms of greater QPS, lower latency, and lower memory consumption.
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### Goals
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* Bump up CoreDNS to be GA.
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* Make CoreDNS available as an image in a Kubernetes repository (To Be Defined) and ensure a workflow/process to update the CoreDNS versions in the future.
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May be deferred to [next KEP](https://github.com/kubernetes/community/pull/2167) if goal not achieved in time.
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* Provide a kube-dns to CoreDNS upgrade path with configuration translation in `kubeadm`.
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* Provide a CoreDNS to CoreDNS upgrade path in `kubeadm`.
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### Non-Goals
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* Translation of CoreDNS ConfigMap back to kube-dns (i.e., downgrade).
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* Translation configuration of kube-dns to equivalent CoreDNS that is defined outside of the kube-dns ConfigMap. For example, modifications to the manifest or `dnsmasq` configuration.
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* Fate of kube-dns in future releases, i.e. deprecation path.
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* Making [CoreDNS the default](https://github.com/kubernetes/community/pull/2167) in every installer.
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## Proposal
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The proposed solution is to enable the selection of CoreDNS as a GA cluster service discovery DNS for Kubernetes.
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Some of the most used deployment tools have been upgraded by the CoreDNS team, in cooperation of the owners of these tools, to be able to deploy CoreDNS:
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* kubeadm
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* kube-up
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* minikube
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* kops
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For other tools, each maintainer would have to add the upgrade to CoreDNS.
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### Use Cases
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* CoreDNS supports all functionality of kube-dns and also addresses [several use-cases kube-dns lacks](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/network/coredns.md#use-cases). Some of the Use Cases are as follows:
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* Supporting [Autopath](https://coredns.io/plugins/autopath/), which reduces the high query load caused by the long DNS search path in Kubernetes.
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* Making an alias for an external name [#39792](https://github.com/kubernetes/kubernetes/issues/39792)
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* By default, the user experience would be unchanged. For more advanced uses, existing users would need to modify the ConfigMap that contains the CoreDNS configuration file.
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* Since CoreDNS has more supporting features than kube-dns, there will be no path to retain the CoreDNS configuration in case a user wants to switch to kube-dns.
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#### Configuring CoreDNS
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The CoreDNS configuration file is called a `Corefile` and syntactically is the same as a [Caddyfile](https://caddyserver.com/docs/caddyfile). The file consists of multiple stanzas called _server blocks_.
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Each of these represents a set of zones for which that server block should respond, along with the list of plugins to apply to a given request. More details on this can be found in the
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[Corefile Explained](https://coredns.io/2017/07/23/corefile-explained/) and [How Queries Are Processed](https://coredns.io/2017/06/08/how-queries-are-processed-in-coredns/) blog entries.
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The following can be expected when CoreDNS is graduated to GA.
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#### Kubeadm
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* The CoreDNS feature-gates flag will be marked as GA.
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* As Kubeadm maintainers chose to deploy CoreDNS as the default Cluster DNS for Kubernetes 1.11:
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* CoreDNS will be installed by default in a fresh install of Kubernetes via kubeadm.
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* For users upgrading Kubernetes via kubeadm, it will install CoreDNS by default whether the user had kube-dns or CoreDNS in a previous kubernetes version.
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* In case a user wants to install kube-dns instead of CoreDNS, they have to set the feature-gate of CoreDNS to false. `--feature-gates=CoreDNS=false`
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* When choosing to install CoreDNS, the configmap of a previously installed kube-dns will be automatically translated to the equivalent CoreDNS configmap.
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#### Kube-up
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* CoreDNS will be installed when the environment variable `CLUSTER_DNS_CORE_DNS` is set to `true`. The default value is `false`.
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#### Minikube
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* CoreDNS to be an option in the add-on manager, with CoreDNS disabled by default.
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## Graduation Criteria
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* Verify that all e2e conformance and DNS related tests (xxx-kubernetes-e2e-gce, ci-kubernetes-e2e-gce-gci-ci-master and filtered by `--ginkgo.skip=\\[Slow\\]|\\[Serial\\]|\\[Disruptive\\]|\\[Flaky\\]|\\[Feature:.+\\]`) run successfully for CoreDNS.
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None of the tests successful with Kube-DNS should be failing with CoreDNS.
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* Add CoreDNS as part of the e2e Kubernetes scale runs and ensure tests are not failing.
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* Extend [perf-tests](https://github.com/kubernetes/perf-tests/tree/master/dns) for CoreDNS.
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* Add a dedicated DNS related tests in e2e scalability test [Feature:performance].
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## Implementation History
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* 20170912 - [Feature proposal](https://github.com/kubernetes/features/issues/427) for CoreDNS to be implemented as the default DNS in Kubernetes.
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* 20171108 - Successfully released [CoreDNS as an Alpha feature-gate in Kubernetes v1.9](https://github.com/kubernetes/kubernetes/pull/52501).
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* 20180226 - CoreDNS graduation to Incubation in CNCF.
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* 20180305 - Support for Kube-dns configmap translation and move up [CoreDNS to Beta](https://github.com/kubernetes/kubernetes/pull/58828) for Kubernetes v1.10.
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