RETIRED: please see the newer version that includes multiple feature store types at https://github.com/rgm/hyak2
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A drop-in Clojure adaptation of Flipper for feature flagging.
Pete Hodgson has a great overview of why you should consider using feature flags, and how not to get burned by them.
Respects Flipper's Redis implementation, so that you can still use the existing Ruby admin web UI and API to manage the Redis store.
(require '[hyak.core :as hyak])
;; the Redis feature store allows the flags to be shared across multiple
;; appservers, etc.
(def fstore (hyak/make-fstore {:pool {} :spec {:url "redis://localhost:6739/1"}}
"feature_flippers")) ;; to match Flipper's defaults
;; fake users aka. actors for the gates below
(def enabled-actor {:id 1000 :username "willy"})
(def disabled-actor {:id 1001 :username "shamu"})
(def MY-FEATURE-FLAG "my_great_new_feature")
(hyak/add! fstore MY-FEATURE-FLAG)
(hyak/enabled? fstore MY-FEATURE-FLAG) ;; => false
;; boolean gate
;; Feature is either on or off for all users, but checked at runtime.
(hyak/enable! fstore MY-FEATURE-FLAG)
(hyak/enabled? fstore MY-FEATURE-FLAG) ;; => true
(hyak/disable! fstore MY-FEATURE-FLAG)
;; actor gate
;; Is a actor's identifier in a set of users who get the feature? Good for
;; previewing features to known users.
(hyak/enable-actor! fstore MY-FEATURE-FLAG 1001)
(hyak/enabled? fstore MY-FEATURE-FLAG (:id enabled-actor)) ;; => true
(hyak/enabled? fstore MY-FEATURE-FLAG (:id disabled-actor)) ;; => false
(hyak/disable! fstore MY-FEATURE-FLAG)
;; percentage of actors gate
;; Is the actor in a (deterministic) partition of n % of the users?
;; (we use `mod 100` on a numeric checksum of the supplied actor identifier, so an
;; actor in the enabled set will stay in the set over successive calls). Good
;; for gradually rolling out UI features.
(hyak/enable-percentage-of-actors! fstore MY-FEATURE-FLAG 50)
(hyak/enabled? fstore MY-FEATURE-FLAG (:username enabled-actor)) ;; => true
(hyak/enabled? fstore MY-FEATURE-FLAG (:username disabled-actor)) ;; => false
(hyak/disable! fstore MY-FEATURE-FLAG)
;; percentage of time gate
;; Randomly make some percentage of all requests enable the feature, without
;; regard for the actor. Good for gradually bringing up load on backend
;; features that tax the system, but where we otherwise don't care who uses it.
(hyak/enable-percentage-of-time! fstore MY-FEATURE-FLAG 10)
(let [tries 1000]
(/ (count (filter true? (repeatedly tries #(hyak/enabled? fstore MY-FEATURE-FLAG))))
tries)) ;; => should expect somewhere near 0.1
(hyak/disable! fstore MY-FEATURE-FLAG)