33 lines
2.1 KiB
Markdown
33 lines
2.1 KiB
Markdown
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# Feature Flags
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Legendary comes with [Fun with Flags](https://github.com/tompave/fun_with_flags)
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preconfigured for managing [feature flags](https://en.wikipedia.org/wiki/Feature_toggle).
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This allows you to have more granular control over which users see which features
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and when. For example, you can hide a feature which is not complete, or show it
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to only a select group of testers.
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Fun With Flags supports a variety of different feature gate types. From
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the Fun With Flags docs:
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* **Boolean**: globally on and off.
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* **Actors**: on or off for specific structs or data. The `FunWithFlags.Actor` protocol can be implemented for types and structs that should have specific rules. For example, in web applications it's common to use a `%User{}` struct or equivalent as an actor, or perhaps the current country of the request.
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* **Groups**: on or off for structs or data that belong to a category or satisfy a condition. The `FunWithFlags.Group` protocol can be implemented for types and structs that belong to groups for which a feature flag can be enabled or disabled. For example, one could implement the protocol for a `%User{}` struct to identify administrators.
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* **%-of-Time**: globally on for a percentage of the time. It ignores actors and groups. Mutually exclusive with the %-of-actors gate.
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* **%-of-Actors**: globally on for a percentage of the actors. It only applies when the flag is checked with a specific actor and is ignored when the flag is checked without actor arguments. Mutually exclusive with the %-of-time gate.
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Since feature flags may be checked often (sometimes multiple times per request),
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Fun With Flags uses a two-layer approach. Flags are cached in [ETS](https://erlang.org/doc/man/ets.html)
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and also persisted to longer-term storage so that they are not lost when the app
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restarts.
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By default, Legendary caches the flags for five minutes. We use Ecto for
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persistence. We also use Phoenix PubSub to inform application nodes when a flag
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has been updated. This configuration is a sensible default that we would not
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expect you to need to change in most cases.
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## UI
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We integrate the Fun With Flags UI for managing flags. You can reach it through
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a link in the admin.
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