037d8c071c
This records the feature flag process we intend to use with Riot and also how that interacts with other teams and configuration. Fixes https://github.com/vector-im/riot-web/issues/11116
89 lines
3.2 KiB
Markdown
89 lines
3.2 KiB
Markdown
# Feature flags
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When developing new features for Riot, we use feature flags to give us more
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flexibility and control over when and where those features are enabled.
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For example, flags make the following things possible:
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* Extended testing of a feature via labs on develop
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* Enabling features when ready instead of the first moment the code is released
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* Testing a feature with a specific set of users (by enabling only on a specific
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Riot instance)
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The size of the feature controlled by a feature flag may vary widely: it could
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be a large project like reactions or a smaller change to an existing algorithm.
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A large project might use several feature flags if it's useful to control the
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deployment of different portions independently.
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Everyone involved in a feature (engineering, design, product, reviewers) should
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think about its deployment plan up front as best as possible so we can have the
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right feature flags in place from the start.
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## Interaction with spec process
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Historically, we have often used feature flags to guard client features that
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depend on unstable spec features. Unfortunately, there was never clear agreement
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about how long such a flag should live for, when it should be removed, etc.
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Under the [new spec
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process](https://github.com/matrix-org/matrix-doc/pull/2324), server-side
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unstable features can be used by clients and enabled by default as long as
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clients commit to doing the associated clean up work once a feature stabilises.
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## Starting work on a feature
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When starting work on a feature, we should create a matching feature flag:
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* Add a new
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[setting](https://github.com/matrix-org/matrix-react-sdk/blob/develop/src/settings/Settings.js)
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of the form:
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```js
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"feature_cats": {
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isFeature: true,
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displayName: _td("Adds cats everywhere"),
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supportedLevels: LEVELS_FEATURE,
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default: false,
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},
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```
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* Check whether the feature is enabled as appropriate:
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```js
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SettingsStore.isFeatureEnabled("feature_cats")
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```
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* Add the feature to the [set of labs on develop](../riot.im/develop/config.json):
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```json
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"features": {
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"feature_cats": "labs"
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},
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```
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* Document the feature in the [labs documentation](labs.md)
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With these steps completed, the feature is disabled by default, but can be
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enabled on develop by interested users for testing.
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Different features may have different deployment plans for when to enable where. The
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following lists a few common options.
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## Enabling by default on develop
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Set the feature to `enable` in the [develop config](../riot.im/develop/config.json):
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```json
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"features": {
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"feature_cats": "enable"
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},
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```
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## Enabling by default on staging and app
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Set the feature to `enable` in the [app config](../riot.im/app/config.json).
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## Feature deployed successfully
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Once we're confident that a feature is working well, we should remove the flag:
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* Remove the [setting](https://github.com/matrix-org/matrix-react-sdk/blob/develop/src/settings/Settings.js)
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* Remove all `isFeatureEnabled` lines that test for the feature's setting
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* Remove the feature from the [labs documentation](labs.md)
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* Remove feature state from [develop](../riot.im/develop/config.json) and
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[app](../riot.im/app/config.json) configs
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* Celebrate! 🥳
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