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| --- | ||
| kep-number: 10 | ||
| title: Graduate CoreDNS to GA | ||
| authors: | ||
| - "@johnbelamaric" | ||
| - "@rajansandeep" | ||
| owning-sig: sig-network | ||
| participating-sigs: | ||
| - sig-cluster-lifecycle | ||
| reviewers: | ||
| - "@bowei" | ||
| - "@thockin" | ||
| approvers: | ||
| - "@thockin" | ||
| editor: "@rajansandeep" | ||
| creation-date: 2018-03-21 | ||
| last-updated: 2018-05-18 | ||
| status: provisional | ||
| see-also: https://github.com/kubernetes/community/pull/2167 | ||
| --- | ||
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| # Graduate CoreDNS to GA | ||
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| ## Table of Contents | ||
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| * [Summary](#summary) | ||
| * [Motivation](#motivation) | ||
| * [Goals](#goals) | ||
| * [Non-Goals](#non-goals) | ||
| * [Proposal](#proposal) | ||
| * [User Cases](#use-cases) | ||
| * [Graduation Criteria](#graduation-criteria) | ||
| * [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 | ||
| authoritative DNS server and directly integrates with the Kubernetes API. It can serve as cluster DNS, | ||
| complying with the [dns spec](https://git.k8s.io/dns/docs/specification.md). As an independent project, | ||
| 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. | ||
| 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. | ||
| * CoreDNS is easily extensible and maintainable using a plugin architecture. | ||
| * CoreDNS has fewer moving parts than kube-dns, taking advantage of the plugin architecture, making it a single executable and single process. | ||
| * It is written in Go, making it memory-safe (kube-dns includes dnsmasq which is not). | ||
| * 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. | ||
| * 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. | ||
| May be deferred to [next KEP](https://github.com/kubernetes/community/pull/2167) if goal not achieved in time. | ||
| * Provide a kube-dns to CoreDNS upgrade path with configuration translation in `kubeadm`. | ||
| * 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). | ||
| * 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. | ||
| * Fate of kube-dns in future releases, i.e. deprecation path. | ||
| * 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. | ||
| 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: | ||
| * kubeadm | ||
| * kube-up | ||
| * minikube | ||
| * 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: | ||
| * Supporting [Autopath](https://coredns.io/plugins/autopath/), which reduces the high query load caused by the long DNS search path in Kubernetes. | ||
| * 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. | ||
| * 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_. | ||
| 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 | ||
| [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. | ||
| * As Kubeadm maintainers chose to deploy CoreDNS as the default Cluster DNS for Kubernetes 1.11: | ||
| * CoreDNS will be installed by default in a fresh install of Kubernetes via kubeadm. | ||
| * 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. | ||
| * 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` | ||
| * 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. | ||
| None of the tests successful with Kube-DNS should be failing with CoreDNS. | ||
| * Add CoreDNS as part of the e2e Kubernetes scale runs and ensure tests are not failing. | ||
| * Extend [perf-tests](https://github.com/kubernetes/perf-tests/tree/master/dns) for CoreDNS. | ||
| * 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. | ||
| * 20171108 - Successfully released [CoreDNS as an Alpha feature-gate in Kubernetes v1.9](https://github.com/kubernetes/kubernetes/pull/52501). | ||
| * 20180226 - CoreDNS graduation to Incubation in CNCF. | ||
| * 20180305 - Support for Kube-dns configmap translation and move up [CoreDNS to Beta](https://github.com/kubernetes/kubernetes/pull/58828) for Kubernetes v1.10. |