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Component feature config design proposal
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| <img src="http://kubernetes.io/kubernetes/img/warning.png" alt="WARNING" | ||
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| <h2>PLEASE NOTE: This document applies to the HEAD of the source tree</h2> | ||
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| If you are using a released version of Kubernetes, you should | ||
| refer to the docs that go with that version. | ||
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| Documentation for other releases can be found at | ||
| [releases.k8s.io](http://releases.k8s.io). | ||
| </strong> | ||
| -- | ||
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| # Overview | ||
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| Proposes adding a `--feature-config` to core kube system components: | ||
| apiserver , scheduler, controller-manager, kube-proxy, and selected addons. | ||
| This flag will be used to enable/disable alpha features on a per-component basis. | ||
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| ## Motivation | ||
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| Motivation is enabling/disabling features that are not tied to | ||
| an API group. API groups can be selectively enabled/disabled in the | ||
| apiserver via existing `--runtime-config` flag on apiserver, but there is | ||
| currently no mechanism to toggle alpha features that are controlled by | ||
| e.g. annotations. This means the burden of controlling whether such | ||
| features are enabled in a particular cluster is on feature implementors; | ||
| they must either define some ad hoc mechanism for toggling (e.g. flag | ||
| on component binary) or else toggle the feature on/off at compile time. | ||
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| By adding a`--feature-config` to all kube-system components, alpha features | ||
| can be toggled on a per-component basis by passing `enableAlphaFeature=true|false` | ||
| to `--feature-config` for each component that the feature touches. | ||
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| ## Design | ||
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| The following components will all get a `--feature-config` flag, | ||
| which loads a `config.ConfigurationMap`: | ||
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| - kube-apiserver | ||
| - kube-scheduler | ||
| - kube-controller-manager | ||
| - kube-proxy | ||
| - kube-dns | ||
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| (Note kubelet is omitted, it's dynamic config story is being addressed | ||
| by #29459). Alpha features that are not accessed via an alpha API | ||
| group should define an `enableFeatureName` flag and use it to toggle | ||
| activation of the feature in each system component that the feature | ||
| uses. | ||
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| ## Suggested conventions | ||
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| This proposal only covers adding a mechanism to toggle features in | ||
| system components. Implementation details will still depend on the alpha | ||
| feature's owner(s). The following are suggested conventions: | ||
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| - Naming for feature config entries should follow the pattern | ||
| "enable<FeatureName>=true". | ||
| - Features that touch multiple components should reserve the same key | ||
| in each component to toggle on/off. | ||
| - Alpha features should be disabled by default. Beta features may | ||
| be enabled by default. Refer to docs/devel/api_changes.md#alpha-beta-and-stable-versions | ||
| for more detailed guidance on alpha vs beta. | ||
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| ## Upgrade support | ||
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| As the primary motivation for cluster config is toggling alpha | ||
| features, upgrade support is not in scope. Enabling or disabling | ||
| a feature is necessarily a breaking change, so config should | ||
| not be altered in a running cluster. | ||
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| ## Future work | ||
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| 1. The eventual plan is for component config to be managed by versioned | ||
| APIs and not flags (#12245). When that is added, toggling of features | ||
| could be handled by versioned component config and the component flags | ||
| deprecated. | ||
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| []() | ||
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